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4.3.1 Description of an Anechoic Chamber
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An Anechoic Chamber is an enclosure, usually shielded, whose internal walls, floor and ceiling are covered with radio absorbing material, normally of the pyramidal urethane foam type. The chamber usually contains an antenna support at one end and a turntable at the other. A typical Anechoic Chamber is shown in figure 3. Turntable Test antenna Antenna support Antenna support Radio absorbing material Range length 3 m or 10 m Figure 3: A typical Anechoic Chamber The chamber shielding and radio absorbing material work together to provide a controlled environment for testing purposes. This type of test chamber attempts to simulate free space conditions. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 21 The shielding provides a test space, with reduced levels of interference from ambient signals and other outside effects, whilst the radio absorbing material minimizes unwanted reflections from the walls and ceiling which can influence the measurements. In practice it is relatively easy for shielding to provide high levels (80 dB to 140 dB) of ambient interference rejection, normally making ambient interference negligible. No design of radio absorbing material, however, satisfies the requirement of complete absorption of all the incident power (it cannot be perfectly manufactured and installed) and its return loss (a measure of its efficiency) varies with frequency, angle of incidence and in some cases, is influenced by high power levels of incident radio energy. To improve the return loss over a broader frequency range, ferrite tiles, ferrite grids and hybrids of urethane foam and ferrite tiles are used with varying degrees of success. The Anechoic Chamber generally has several advantages over other test facilities. There is minimal ambient interference, minimal floor, ceiling and wall reflections and it is independent of the weather. It does however have some disadvantages which include limited measuring distance and limited lower frequency usage due to the size of the pyramidal absorbers. Both absolute and relative measurements can be performed in an Anechoic Chamber. Where absolute measurements are to be carried out, or where the test facility is to be used for accredited measurements, the chamber should be verified. The verification procedure involves the transmission of a known signal level from one calibrated antenna (usually a dipole) at a specified fixed height on the turntable and the measurement of the received signal level in a second calibrated antenna (also usually a dipole). By comparison of the transmitted and received signal levels, an "insertion loss" can be deduced. After inclusion of any correction factors to the measurement, the figure of loss which results from the verification procedure, is known as "Site Attenuation". A comparison is then made of the measured performance to that of an ideal theoretical chamber, with acceptability being decided on the basis of the differences not exceeding some pre-determined limits. A fully detailed procedure for verifying the performance of an Anechoic Chamber is given in ETR 273 [6]. Field uniformity in an Anechoic Chamber resulting from constructive and destructive interference of the direct and any residual reflected fields can be minimal, but will still vary, depending on the quality of the absorber, in amplitude, phase, impedance and polarization from one measurement point to another and from one frequency to another within the test volume or test area. All types of emission, sensitivity and immunity testing can be carried out within an Anechoic Chamber without limitation although it is more usual for adjacent channel power and most immunity testing to be performed in a Test Fixture.
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4.3.2 Description of an Anechoic Chamber with a ground plane
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An Anechoic Chamber with a ground plane is an enclosure, usually shielded, whose internal walls and ceiling are covered with radio absorbing material, normally of the pyramidal urethane foam type. The floor, which is metallic, is not covered and forms the ground plane. The chamber usually contains an antenna mast at one end and a turntable at the other. A typical Anechoic Chamber with a ground plane is shown in figure 4. This type of test chamber attempts to simulate an ideal Open Area Test Site (historically, the reference site upon which the majority, if not all, of the specification limits have been set) whose primary characteristic is a perfectly conducting ground plane of infinite extent. The chamber shielding and radio absorbing material work together (in the same manner as described in subclause 4.3.1) to provide a controlled environment for testing purposes. Both absolute and relative measurements can be performed in an Anechoic Chamber with a ground plane. Where absolute measurements are to be carried out, or where the test facility is to be used for accredited measurements, the chamber should be verified. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 22 The verification procedure involves the transmission of a known signal level from one calibrated antenna (usually a dipole) at a specified fixed height on the turntable and the measurement of the received signal level in a second calibrated antenna (also usually a dipole) which has been "peaked" by raising and lowering the antenna on the mast to obtain the maximum constructive interference of the direct and reflected signals from the transmitting antenna. By comparison of the transmitted and received signal levels, an "insertion loss" can be deduced. After inclusion of any correction factors to the measurement, the figure of loss which results from the verification procedure, is known as "Site Attenuation". A comparison is then made of the measured performance to that of an ideal theoretical chamber, with acceptability being decided on the basis of the differences not exceeding some pre-determined limits. A fully detailed procedure for verifying the performance of an Anechoic Chamber with a ground plane is given in ETR 273 [6]. Range length 3 m or 10 m Turntable Test antenna Antenna mast Ground plane Radio absorbing material Figure 4: A typical Anechoic Chamber with a ground plane In this facility the ground plane creates the wanted reflection path, such that the signal received by the receiving antenna is the sum of the signals from both the direct and reflected transmission paths. This creates a unique received signal level for each height of the transmitting antenna (or EUT) and the receiving antenna above the ground plane. In use, the antenna mast provides a variable height facility so that the elevation height of the test antenna can be optimized for maximum coupled signal between antennas or between an EUT and the test antenna. Under these conditions, emission testing involves firstly "peaking" the field strength from the EUT by raising and lowering the receiving antenna on the mast (to obtain the maximum constructive interference of the direct and reflected signals from the EUT) and then rotating the turntable for a "peak" in the azimuth plane. At this height of the test antenna on the mast, the amplitude of the received signal is noted. Secondly the EUT is replaced by a substitution antenna (positioned at the EUT's phase or volume centre) which is connected to a signal generator. The signal is again "peaked" and the signal generator output adjusted until the level, noted in stage one, is again measured on the receiving device. Receiver sensitivity tests over a ground plane also involve "peaking" the field strength by raising and lowering the test antenna on the mast to obtain the maximum constructive interference of the direct and reflected signals, this time using a measuring antenna which has been positioned where the phase or volume centre of the EUT will be during testing. A transform factor is derived. The test antenna remains at the same height for stage two, during which the measuring antenna is replaced by the EUT. The amplitude of the transmitted signal is reduced to determine the field strength level at which a specified response is obtained from the EUT. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 23 The field uniformity due to constructive or destructive interference of the direct and reflected fields, may vary considerably in amplitude, phase, impedance and polarization from one measurement point to another and from one frequency to another within the test volume. For this reason, immunity tests (involving two or more signals at different frequencies) should not be carried out in an Anechoic Chamber with a ground plane since the interference makes it is difficult to sweep the frequency and maintain a constant field strength at the EUT.
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4.3.3 Description of an Open Area Test Site
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An Open Area Test Site comprises a turntable at one end and an antenna mast of variable height at the other set above a ground plane which, in the ideal case, is perfectly conducting and of infinite extent. In practice, whilst good conductivity can be achieved, the ground plane size has to be limited. A typical Open Area Test Site is shown in figure 5. Range length 3 or 10 m Turntable Ground plane Dipole antennas Antenna mast Figure 5: A typical Open Area Test Site The ground plane creates a wanted reflection path, such that the signal received by the receiving antenna is the sum of the signals received from the direct and reflected transmission paths. The phasing of these two signals creates a unique received level for each height of the transmitting antenna (or EUT) and the receiving antenna above the ground plane. In practice, the antenna mast provides a variable height facility so that the position of the test antenna can be optimized for maximum coupled signal between antennas or between an EUT and the test antenna. Both absolute and relative measurements can be performed on an Open Area Test Site. Where absolute measurements are to be carried out, or where the test facility is to be used for accredited measurements, the Open Area Test Site should be verified. The verification procedure involves the transmission of a known signal level from one calibrated antenna (usually a dipole) at a specified fixed height on the turntable and the measurement of the received signal level in a second calibrated antenna (also usually a dipole) which has been "peaked" by raising and lowering the antenna on the mast to obtain the maximum constructive interference of the direct and reflected signals from the transmitting antenna. By comparison of the transmitted and received signal levels, an "insertion loss" can be deduced. After inclusion of any correction factors to the measurement, the figure of loss which results from the verification procedure, is known as "Site Attenuation". A comparison is then made of the measured performance to that of an ideal theoretical chamber, with acceptability being decided on the basis of the differences not exceeding some pre-determined limits. A fully detailed procedure for verifying the performance of an Open Area Test Site is given in ETR 273 [6]. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 24 For a discussion of the practicalities of emission, sensitivity and immunity testing on an Open Area Test Site, reference should be made to subclause 4.3.2 since the considerations are the same as for an Anechoic Chamber with a ground plane. The Open Area Test Site is, historically, the reference site upon which the majority, if not all, of the specification limits have been set. The ground plane was introduced for uniformity of ground conditions, between test sites, during testing.
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4.3.4 Description of Striplines
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A Stripline is essentially a transmission line in the same sense as a coaxial cable. It sets up an electromagnetic field between the plates in a similar way that a coaxial cable sets up fields between inner and outer conductors. In both cases, the basic mode of propagation is in the form of a transverse electromagnetic wave (TEM) i.e. a wave which possesses single electric and magnetic field components, transverse to the direction of propagation, as in the case of propagation in free-space. Stripline test facilities, therefore, are transmission lines constructed with their plates separated sufficiently for an EUT to be inserted between them. There are various types of Stripline test facilities, mainly comprising either 2 or 3 plates. The 3 plate designs are available as either open or closed i.e. the fields can either extend into the region surrounding the line or they can be totally enclosed by metal side plates. Typical 2 and 3-plate open Striplines are shown in figure 6. For the 3-plate open cell, the middle plate can be either symmetrically spaced between the outer two (as shown in figure 6), or offset more towards the bottom or top plate. 2-plate 3-plate Centre plate Figure 6: Typical open 2-plate and 3-plate Stripline test facilities For all versions of the open Stripline, some portion of the electromagnetic field extends beyond the physical extent of the line since the sides are not enclosed by metal. As a direct consequence, the performance of an open cell is dependent not only on its construction but also on its immediate environment - the cell interacting with physical objects which may be present e.g. test equipment, people, etc., as well as suffering from the influences of external electrical effects such as local ambient signals and resonances of the room in which the cell is located. Shielding the room has the benefit of eliminating ambient signals but can seriously increase the magnitude of the room resonance effects (the room acting like a large resonant waveguide cavity). Where a shielded room is used to locate the open Stripline, strategic use of absorbing panels (for damping resonance effects and generally reducing other interactions) is regarded as essential. Use of an open Stripline in a non-shielded room may cause interference to others. A typical closed Stripline (alternatively termed TEM cell) is shown in figure 7. The TEM cell is constructed using 5 plates, i.e. a central conductor in addition to four sides. Benefits, resulting from the enclosure on all four sides, include the elimination of effects due to external reflections, local ambient signals and room resonances suffered by the open Stripline. Drawbacks include internally generated resonances and a dramatic cost increase relative to the equivalent open version. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 25 Access door Centre plate Side plate Figure 7: A typical closed Stripline test facility A Stripline test facility needs a room much larger than itself in which to be installed. Room resonances can be encountered in rooms of rectangular cross-section at all frequencies satisfying the following formula: f x l y b z h = + + 150 2 2 2 MHz Here l, b and h are the length, breadth and height of the room in metres and x, y and z are mode numbers. The only condition limiting the use of this formula is that only one of x, y or z can be zero at any one time. For a room measuring 8 m × 8 m × 4 m, there are 25 resonant frequencies within the band 26,5 MHz to 120,1 MHz. This shows that, in principle, room resonances can pose major problems. Their effects are worse for rooms which are metal lined for shielding from ambient signals. In this condition, the room acts like a waveguide and will possess high Q-factors for some or all resonant frequencies. Their effects are to put sharp spikes into the field strength variation with frequency within the cells. In general, these can only be damped by the use of absorbing material placed around the cell. Other factors which can contribute to disturbance of the field within the Stripline include cabling (in terms of reflections and its possible parasitic effect) and local ambient effects. In general, to keep cabling problems to a minimum, these should be as short as possible within the Stripline, gain access to the test area via small holes in the bottom plate and be heavily loaded with ferrite beads. To completely nullify ambient signals, a shielded room is required but the above discussion of resonances should be borne in mind.
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4.3.5 Discussion of a Test Fixture
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A Test Fixture is, in most cases, individually constructed for testing a specific equipment type. It consists of a 50 ΩRF connector and a device for electromagnetically coupling to the EUT. It should also incorporate a means for repeatable positioning of the EUT. Figure 8 illustrates a typical Test Fixture. Low dielectric constant material Electromagnetic coupling "Probe" RF connector 50 Ω Figure 8: Basic, typical Test Fixture The coupling device usually comprises a small antenna that is placed, physically and electrically, close to the EUT. This antenna/coupling device is used for sampling or generating the test fields when the EUT is undergoing testing at extreme conditions of temperature and/or voltage. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 26 Test fixtures should be constructed in such a way that measurements are repeatable. This requires some specific mounting arrangements to be incorporated within the Test Fixture to secure the EUT in a fixed position. Such mounting arrangements would additionally help to maintain the relative polarization between the EUT and the coupling device. A typical scheme is shown in figure 9. Power/signal leads plus ferrite beads EUT Figure 9: EUT mounted in a typical Test Fixture A Test Fixture should enable adequate access to the EUT for interfacing with the test equipment. In particular, it should provide, where relevant, access to: - the "press to talk" button for a transmitter; - the modulator input for a transmitter; - the audio output for a receiver; - the power terminals for connection to an external power supply. The entire assembly of Test Fixture plus EUT is generally extremely compact and it can be regarded as a miniature test site. Its compactness enables the whole assembly to be accommodated within a test chamber (usually a climatic facility) that completely encloses the extreme condition. The circuitry associated with the RF coupling device should contain no active or non-linear components and should present a VSWR of better than 1,5:1 to a 50 Ωline.
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4.3.5.1 Performance limitations
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The coupling mechanism between the EUT and the Test Fixture is extremely complex since the two are placed physically and electrically very close together. This complexity makes any attempt at theoretically modelling a Test Fixture's performance not only very difficult but also time consuming and costly. In practise, therefore, modelling is seldom attempted. The direct consequence of this is that absolute measurements cannot be made in a Test Fixture and any measurement results have to be related, in some way, to baseline results taken on a Free-Field Test Site. The usual way to relate the results is by a process, sometimes referred to as field equalization, in which the relevant parameter (effective radiated power, receiver sensitivity, etc.) is initially measured on a Free-Field Test Site under normal conditions and then subsequently re-measured using only the Test Fixture (with the EUT installed) also under normal conditions. The difference (in dB) of the two results (received signal level for an effective radiated power test, output power from a signal generator for a sensitivity test) is termed the coupling factor of the Test Fixture and provides the link between all the results of EUT tests carried out in the Test Fixture and its performance on a verified Free-Field Test Site. As a general rule, the coupling factor should not be greater than 20 dB. To reiterate, this key limitation for a Test Fixture can be stated in two ways: - only relative measurements can be made; - absolute measurements cannot be made. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 27 A further limitation to the use of a Test Fixture results from the unknown variation of the coupling factor with frequency. This variation cannot be relied upon to be linear over large bandwidths and this puts a limit on those tests which can be accurately carried out. As a result, emission tests are generally limited to the nominal frequencies (for which the performance of the Test Fixture has been verified) of low power devices for effective radiated power and frequency error tests. Occasionally, however, adjacent channel power is tested. Similarly, receiver tests are normally limited to receiver sensitivity although, occasionally, co-channel rejection, adjacent channel selectivity, inter-modulation immunity and blocking are tested. Ideally, all Test Fixtures should be verified and where EUT testing will be required over a frequency band, the verification procedure should be extended to include the frequencies at the band edges. In any case, routine verification, perhaps every 6 months, should be carried out as a means of detecting any deterioration/change in performance. A fully detailed procedure for verifying the performance of a Test Fixture is given in ETR 273 [6]. Local ambient signals can potentially be problematic to measurements carried out in a Test Fixture, although very little uncertainty is introduced into transmitter tests, since EUT power levels will dominate. However, for receiver tests (i.e. sensitivity and various types of immunity testing) shielding may be required. Adequate shielding can be achieved by either using the Test Fixture within a metalized test chamber (e.g. climatic facility) or by enclosing it within a shielded room. In either case, one shall however be aware of the possible frequencies of resonance for these structures. Only integral antenna devices are tested in a Test Fixture. For devices possessing either permanent or temporary external RF connectors, all testing is carried out using conducted methods.
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4.4 Salty columns/artificial human beings
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There are several forms of artificial human beings currently used in radiated testing. The three most commonly used types are the Saltwater column, the Salty man and Salty-lite. The Saltwater column has historically been used not only for testing body-worn devices e.g. paging receivers, but also for tests on maritime and other mobile equipment. It was the first in existence and is mainly used in measurements on body-worn equipment operating below 50 MHz. At higher frequencies, many tests are currently performed using two types of Salty man which are basically saltwater filled plastic cylinders of the height of an average adult.
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4.4.1 Saltwater column
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A Saltwater column comprises a plastic cylinder of side wall thickness 0,005 m, overall height 1,5 m and of inside diameter typically 0,01 m filled with a saline solution whose concentration of salt (NaCl) is 9,0 g per litre of distilled water (see figure 10). The Saltwater column has been used with the EUT either fixed to the side of the column (to simulate belt-worn or breast pocket-worn devices) or mounted on a hinged metal mounting bracket on the top metal mounting plate which enables an EUT to be oriented at various angles during measurements. Metal cap 0,015m dia. Saline solution Acrylic cylinder Hinged plate 1,5m 0,01m ID 9gm/ltr NaCl Acrylic end cap Figure 10: Typical saltwater column ETSI ETSI TR 100 027 V1.2.1 (1999-12) 28 No theoretical or experimental data concerning the Saltwater column has been found and due to its obvious dissimilarity with the human body, and the lack of data supporting its usage, it is recommended that the Saltwater column should not be used for body-worn equipment tests. The following discussions are therefore limited to the merits of Salty man and Salty-lite and the recommended frequency limitations of their use on Free-Field Test Sites.
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4.4.2 Salty man
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A "Salty man", illustrated in figure 11a), comprises a cast acrylic cylinder of 0,305 m outside diameter with acrylic caps at both ends. It is 1,7 m in length with side wall thickness of 4,8 mm and the whole is filled with a saline solution whose concentration is 1,49 g of salt per litre of distilled water. Figure 11a illustrates the original design of a Salty man as detailed in IEC 489-6, Appendix H [1].
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4.4.3 Salty-lite
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"Salty-lite" is shown in figure 11b) and is a much lighter version of the Salty man (approximately 61,5 kg against 125 kg) which therefore makes it easier to handle and transport. Salty-lite comprises two concentric cast acrylic cylinders, the outer one having an outside diameter of 0,305 m whilst the inner cylinder has an outside diameter of 0,225 m. The outer cylinder is 1,32 m in length whilst the inner one measures 1,52 m. The difference in length is used to form an air-filled head. Only the space between the two cylinders is filled with saline solution which, in early versions, had a similar concentration of salt as the Salty man (1,49 g of salt per litre of distilled water). However, [2] revealed several resonances are evident at this concentration, and experimental and theoretical work [1] showed that these resonances could be damped out by using a concentration of 4g of salt per litre of distilled water. This is the currently recommended concentration and all discussion of Salty-lite's electrical performance given in clauses 4 and 5 assume this more concentrated salt solution. a) Salty Man Acrylic cap 1,7m 1,32m b) Salty-Lite 0,04m Saline solution Air-filled head 4,8mm 0,305m OD 0,225m 1,49gm/ltr NaCl =77 =,26S/m ε σ 4,0gm/ltr NaCl =77 =,70S/m ε σ Acrylic cylinders 0,20m Figure 11: The two types of Salty man ETSI ETSI TR 100 027 V1.2.1 (1999-12) 29
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4.4.4 Test conditions
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The provision of realistic test conditions for Salty man/Salty-lite is extremely difficult. In everyday use of a body-worn equipment, a human being will operate the equipment over a variety of ground types, none of which influences performance in the same way as those provided during testing in either an Anechoic Chamber or on a perfectly reflecting ground plane site. Specifically, the distribution of the illuminating fields over the length of the Salty man/Salty-lite (when used in receiver tests) varies fundamentally with ground type. Whereas the ideal Anechoic Chamber provides a slowly varying amplitude distribution (consistent with the vertical plane radiation pattern of the transmitting antenna) and a phase distribution entirely dependent on the path length geometry (see figure 12), an Open Area Test Site/Anechoic Chamber with a ground plane can, in contrast, provide a wildly varying field distribution. By virtue of the phase of the reflected signal on this ground plane type of site, horizontally and vertically polarized signals are affected differently. Figure 13 shows the distribution of amplitude and phase for a vertically polarized electric field over the length of Salty man/Salty-lite for a typical testing range length of 3 metres over a ground plane. The height of the test antenna has been optimized for a chest worn equipment, assumed to be mounted 1,5 m above the base of the Salty man. Salty man EUT 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 Amplitude, dB Phase, degrees Phase Amplitude Range length 3m Frequency 241,42 MHz Source antenna - Omni 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 0 +40 +80 +120 -40 -80 Height (m) Figure 12: Amplitude and phase distribution along the Salty man over an absorptive ground The figure shows that a deep null in the amplitude of the illuminating electric field occurs at a height of approximately 0,7 m above the base of the Salty man. Additionally, the phase of the illuminating field over the length of the Salty man is far from uniform. One has to question how representative of the real-life performance are the results from tests carried out on this type of facility. On the plus side, it can be seen from figure 5 that in the near vicinity of the EUT the amplitude and phase of the electric field can be seen to be reasonably constant but this may not be sufficient for test purposes. The parameters for determining figure 13 have been selected as a typical example; a test antenna height of 1,5 m giving a field maximum at chest height (also 1,5 m) at a range length of 3 m. For the example frequency of 241,42 MHz, there is no other test antenna height (assuming 1 m to 4 m available height variation) which will produce a peak at chest height. Therefore only one null appears on the Salty man/Salty-lite. However, as the frequency increases more nulls appear. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 30 Salty man EUT 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 Amplitude, dB Phase, degrees Phase Amplitude Range length 3m Frequency 241,42 MHz Source antenna - Omni 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 0 +40 +80 +120 -40 -80 Height (m) Figure 13: Amplitude and phase distribution along the Salty man over a reflective ground For example, above 254,2 MHz there will be at least 2 peaks to choose from for the maximum signal (and hence 2 nulls in the illumination over Salty man/Salty-lite), above 381,4 MHz at least 3 peaks (and 3 nulls), etc., up to above 889,9 MHz where there will be at least 7 peaks to choose from with their 7 associated nulls. Since mutual coupling and extraneous reflections can play a significant role in determining the magnitude of these peaks it cannot be ruled out that, in the worst case, all of these theoretically possible peaks and nulls will be present during testing. The value of a test result taken in this worst case of multiple nulling over the Salty man/Salty-lite is difficult to assess. Conversely, if one imposed the conditions that: - no null should appear in the illumination across Salty man/Salty-lite and; - the maximum amplitude variation should not exceed, say, 5 dB (taken for illustration only), then a 3 m range could only be used for frequencies below about 38,5 MHz and a 10 m range length below about 74,1 MHz. Contrast this testing environment generated on a ground-reflecting range, to that provided by an ideal Anechoic Chamber offering the same range length (shown in figure 12). Here, the illuminating electric field is reasonably constant in both amplitude and phase along the entire length of the salty column - the variations being dependent on the radiation pattern of the test antenna in the vertical plane and the overall geometry for amplitude and phase respectively.
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4.5 Test antenna
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A test antenna is always used in radiated test methods. In emission tests (i.e. frequency error, effective radiated power, spurious emissions and adjacent channel power) the test antenna is used to detect the field from the EUT in one stage of the measurement and from the substitution antenna in the other stage. When the test site is used for the measurement of receiver characteristics (i.e. sensitivity and various immunity parameters) the antenna is used as the transmitting device. The test antenna should be mounted on a support capable of allowing the antenna to be used in either horizontal or vertical polarization which, on ground plane sites (i.e. Anechoic Chambers with ground planes and Open Area Test Sites), should additionally allow the height of its centre above the ground to be varied over the specified range (usually 1 m to 4 m). ETSI ETSI TR 100 027 V1.2.1 (1999-12) 31 In the frequency band 30 MHz to 1 000 MHz, dipole antennas (constructed in accordance with ANSI C63.5 (1988) [11]) are generally recommended. For frequencies of 80 MHz and above, the dipoles should have their arm lengths set for resonance at the frequency of test. Below 80 MHz, shortened arm lengths are recommended. For spurious emission testing, however, a combination of bicones and log periodic dipole array antennas (commonly termed "log periodics") could be used to cover the entire 30 MHz to 1 000 MHz band. Above 1 000 MHz, waveguide horns are recommended although, again, log periodics could be used. NOTE: The gain of a horn antenna is generally expressed relative to an isotropic radiator.
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4.6 Substitution antenna
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The substitution antenna is used to replace the EUT for tests in which a transmitting parameter (i.e. frequency error, effective radiated power, spurious emissions and adjacent channel power) is being measured. For measurements in the frequency band 30 MHz to 1 000 MHz, the substitution antenna should be a dipole antenna (constructed in accordance with ANSI C63.5 (1988) [11]). For frequencies of 80 MHz and above, the dipoles should have their arm lengths set for resonance at the frequency of test. Below 80 MHz, shortened arm lengths are recommended. For measurements above 1 000 MHz, a waveguide horn is recommended. The centre of this antenna should coincide with either the phase centre or volume centre (as specified in the test method) of the EUT it has replaced. NOTE: The gain of a horn antenna is generally expressed relative to an isotropic radiator.
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4.7 Measuring antenna
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The measuring antenna is used in tests on an EUT in which a receiving parameter (i.e. sensitivity and various immunity tests) is being measured. Its purpose is to enable a measurement of the electric filed strength in the vicinity of the EUT. For measurements in the frequency band 30 MHz to 1 000 MHz, the measuring antenna should be a dipole antenna (constructed in accordance with ANSI C63.5 (1988) [11]). For frequencies of 80 MHz and above, the dipoles should have their arm lengths set for resonance at the frequency of test. Below 80 MHz, shortened arm lengths are recommended. The centre of this antenna should coincide with either the phase centre or volume centre (as specified in the test method) of the EUT.
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4.8 Transmitting antenna
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The transmitting antenna is only used in verification procedures on free field test sites. For measurements in the frequency band 30 MHz to 1 000 MHz, the transmitting antenna should be a dipole antenna (constructed in accordance with ANSI C63.5 (1988) [11]). For frequencies of 80 MHz and above, the dipoles should have their arm lengths set for resonance at the frequency of test. Below 80 MHz, shortened arm lengths are recommended. Optionally, a combination of bicones and log periodics could be used to cover the entire 30 MHz to 1 000 MHz band. For verification in the frequency band 1 GHz to 12,75 GHz, log periodics are recommended.
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4.9 Receiving antenna
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The receiving antenna is only used in verification procedures on free field test sites. For measurements in the frequency band 30 MHz to 1 000 MHz, the receiving antenna should be a dipole antenna (constructed in accordance with ANSI C63.5 (1988) [11]). For frequencies of 80 MHz and above, the dipoles should have their arm lengths set for resonance at the frequency of test. Below 80 MHz, shortened arm lengths are recommended. Optionally, a combination of bicones and log periodics could be used to cover the entire 30 MHz to 1 000 MHz band. For verification in the frequency band 1 GHz to 12,75 GHz, log periodics are recommended.
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4.10 Acoustic coupler
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4.10.1 General
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When radiated measurements are performed on a receiving EUT, the audio output voltage should be transmitted from the receiver to the measuring equipment, with minimal perturbation to the field near the receiver. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 32 For EUTs fitted with an "audio out" socket, this perturbation can be minimized by using wires with high associated resistivity and a high input impedance modulation detector. When this situation cannot be achieved, an acoustic coupler should be used. NOTE: When using this acoustic coupler care should be exercised that possible ambient noise does not influence the test result.
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4.10.2 Description
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The acoustic coupler comprises a plastic funnel, an acoustic pipe and a microphone with a suitable amplifier. The materials used to fabricate the funnel and pipe should be of low conductivity and of low relative dielectric constant (i.e. less than 1,5). - The acoustic pipe should be long enough to reach from the EUT to the microphone which should be located in a position that will not disturb the RF field. The acoustic pipe should have an inner diameter of about 6 mm and a wall thickness of about 1,5 mm and should be sufficiently flexible so as not to hinder the rotation of the turntable. - The plastic funnel should have a diameter appropriate to the size of the loudspeaker in the EUT, with soft foam rubber glued to its edge, it should be fitted to one end of the acoustic pipe and the microphone should be fitted to the other end. It is very important to fix the centre of the funnel in a reproducible position relative to the EUT, since the position of the centre has a strong influence on the frequency response that will be measured. This can be achieved by placing the EUT in a close fitting acoustic mounting jig, supplied by the manufacturer, of which the funnel is an integral part. - The microphone should have a response characteristic flat within 1 dB over a frequency range of 50 Hz to 20 kHz, a linear dynamic range of at least 50 dB. The sensitivity of the microphone and the receiver audio output level should be suitable to measure a signal to noise ratio of at least 40 dB at the nominal audio output level of the EUT. Its size should be sufficiently small to couple to the acoustic pipe. - The frequency correcting network should correct the frequency response of the acoustic coupler so that the acoustic SINAD measurement is valid (see IEC 489-3, Appendix F [1]).
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4.10.3 Calibration
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The aim of the calibration of the acoustic coupler is to determine the acoustic SINAD ratio which is equivalent to the SINAD ratio at the receiver output. Signal generator Receiver under test Test Fixture Acoustic pipe Microphone Amplifier and filter SINAD meter 1 2 Figure 14: Measuring arrangement for calibration
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4.10.3.1 Calibration of the acoustic coupler
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a) The acoustic coupler should be mounted close to the EUT which, if necessary, should be mounted in a Test Fixture. A direct electrical connection to the terminals of the output transducer should be made. A signal generator should be connected to the receiver input (or to the Test Fixture input). The signal generator should be at the nominal frequency of the receiver and should be modulated by the test modulation A-M1. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 33 b) Where possible, the receiver volume control should be adjusted to give at least 50 % of the rated audio output power and, in the case of stepped volume controls, to the first step that provides an output power of at least 50 % of the rated audio output power. c) The test signal input level should be reduced until an electrical SINAD ratio of 20 dB is obtained, the connection being in position 1 as shown in figure 14. The signal input level should be recorded. d) With the same signal input level, the acoustic equivalent SINAD ratio should be measured and recorded, the connection being in position 2 as shown in figure 14. e) Steps c) and d) above should be repeated for an electrical SINAD ratio of 14 dB, and the acoustic equivalent SINAD ratio measured and recorded.
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5 Setting up for conducted measurements
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This clause is relevant to conducted measurements only, i.e. those tests which can be made using a direct 50 Ω connection to the EUT. Bit stream measurements should be performed on the "raw" bit stream thus by-passing error correcting coders or decoders unless it is impossible to disassociate one from the other. Message measurements should include error correcting encoders and decoders, if fitted. For EUTs not fitted with an antenna socket, some measurements can be made using a temporary 50 Ωconnector. Details and implications of such a procedure should be stated in the corresponding ETS or EN. When performing transmitter tests on EUT designed for intermittent operation, the specified maximum transmit time should not be exceeded.
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6 Setting up for Radiated tests
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This clause details procedures, test equipment arrangements and recommendations that should be carried out BEFORE any of the radiated test methods given in subclauses 7.2 (for transmitting EUTs) and 8.2 (for receiving EUTs) are performed. Some of these schemes are common to all types of test site, others are relevant to individual sites only.
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6.1 For all types of test site
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The test methods given in subclauses 7.2 and 8.2 apply to integral antenna devices only i.e. EUTs not fitted with either a permanent or a temporary external antenna connector. The Spurious emissions test also applies to EUTs with a detachable antenna.
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6.1.1 Verification of the test site
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No test should be carried out on a test site which does not possess a valid certificate of verification. The verification procedures for all the different types of test site considered in clauses 7 and 8 (i.e. Anechoic Chamber, Anechoic Chamber with a ground plane, Open Area Test Site, Stripline and Test Fixture) are given in ETR 273 [6] along with a similar procedure for verifying the serviceability of the two artificial human bodies, namely Salty man and Salty-lite.
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6.1.2 Preparation of the EUT
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The manufacturer should supply information about the EUT covering the operating frequency, polarization, supply voltage(s) and the reference face. Additional information, specific to the type of EUT should include, where relevant, carrier power, channel spacing, whether different operating modes are available (e.g. high and low power modes) and if operation is continuous or is subject to a maximum test duty cycle (e.g. 1 minute on, 4 minutes off). ETSI ETSI TR 100 027 V1.2.1 (1999-12) 34 Where necessary, a mounting bracket of minimal size should be available for mounting the EUT on the turntable. This bracket should be made from low conductivity, low relative dielectric constant (i.e. less than 1,5) material(s) such as expanded polystyrene, balsawood, etc.
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6.1.3 Power supplies to the EUT
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All tests should be performed using power supplies wherever possible, including tests on EUT designed for battery-only use. In all cases, power leads should be connected to the EUT's supply terminals (and monitored with a digital voltmeter) but the battery should remain present, electrically isolated from the rest of the equipment, possibly by putting tape over its contacts. The presence of these power cables can, however, affect the measured performance of the EUT. For this reason, they should be made to be "transparent" as far as the testing is concerned. This can be achieved by routing them away from the EUT and down to the either the screen, ground plane or facility wall (as appropriate) by the shortest possible paths. Additionally, where possible, these leads should be twisted together and loaded with ferrite beads at 0,15 m spacing.
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6.1.4 Volume control setting for analogue speech tests
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Unless otherwise stated, in all receiver measurements for analogue speech the receiver volume control where possible, should be adjusted to give at least 50 % of the rated audio output power. In the case of stepped volume controls, to volume control should be set to the first step that provides an output power of at least 50 % of the rated audio output power. This control should not be readjusted between normal and extreme test conditions in tests involving the Test Fixture. 6.2 For Anechoic Chambers, Anechoic Chambers with ground planes and Open Area Test Sites only
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6.2.1 Range length
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The range length for these types of test facility should be adequate to allow for testing in the far-field of the EUT i.e. it should be equal to or exceed: ( ) 2 1 2 2 d d + λ where: d1 is the largest dimension of the EUT/dipole after substitution (m); d2 is the largest dimension of the test antenna (m); λ is the test frequency wavelength (m). It should be noted that in the substitution part of this measurement, where both test and substitution antennas are half wavelength dipoles, this minimum range length for far-field testing would be: 2λ It should be noted in the test report when either of these conditions is not met so that the additional measurement uncertainty can be incorporated into the results. NOTE 1: For the fully Anechoic Chamber, no part of the volume of the EUT should, at any angle of rotation of the turntable, fall outside the "quiet zone" of the chamber at the nominal frequency of the test. NOTE 2: The "quiet zone" is a volume within the Anechoic Chamber (without a ground plane) in which a specified performance has either been proven by test, or is guaranteed by the designer/manufacture. The specified performance is usually the reflectivity of the absorbing panels or a directly related parameter (e.g. signal uniformity in amplitude and phase). It should be noted however that the defining levels of the quiet zone tend to vary. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 35 NOTE 3: For the Anechoic Chamber with a ground plane, a full height scanning capability, i.e. 1 m to 4 m, should be available for which no part of the test antenna should come within 1 m of the absorbing panels. For both types of Anechoic Chamber, the reflectivity of the absorbing panels should not be worse than -5 dB. NOTE 4: For both the Anechoic Chamber with a ground plane and the Open Area Test Site, no part of any antenna should come within 0,25 m of the ground plane at any time throughout the tests. Where any of these conditions cannot be met, measurements should not be carried out.
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6.2.2 Site preparation
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The cables for both ends of the test site should be routed horizontally away from the testing area for a minimum of 2 m (unless, in the case both types of Anechoic Chamber, a back wall is reached) and then allowed to drop vertically and out through either the ground plane or screen (as appropriate) to the test equipment. These cables should be dressed with ferrite beads, spaced 0,15 m apart for their entire lengths above the ground plane/screen. The cables, their routing and dressing should be identical to the verification set-up. NOTE: For ground reflection test sites (i.e. Anechoic Chambers with ground planes and Open Area Test Sites) which incorporate a cable drum with the antenna mast, the 2 m requirement may be impossible to comply with. Calibration data for all items of test equipment should be available and valid. For test, substitution and measuring antennas, the data should include gain relative to an isotropic radiator (or antenna factor) for the frequency of test. Also, the VSWR of the substitution and measuring antennas should be known. The calibration data on all cables and attenuators should include insertion loss and VSWR throughout the entire frequency range of the tests. All VSWR and insertion loss figures should be recorded in the log book results sheet for the specific test. Where correction factors/tables are required, these should be immediately available. For all items of test equipment, the maximum errors they exhibit should be known along with the distribution of the error e.g.: • cable loss: ±0,5 dB with a rectangular distribution; • measuring receiver: 1,0 dB (standard deviation) signal level accuracy with a Gaussian error distribution. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 36 Cabling Adaptor Turntable Receiving device 10 dB attenuators Radio absorbing material Signal generator Range length 3 m or 10 m Figure 15: Anechoic Chamber set-up for daily system checking At the start of each day, system checks should be made on the items of test equipment used on the test site. The following checking procedures, as a minimum requirement, should be carried out. 1 All items of test equipment requiring electrical supplies should be connected to their power sources, switched on and allowed adequate time to stabilize, as recommended by the manufacturers. Where a stabilization period is not given by the manufacturer, 30 minutes should be allowed. After this time period, those items of test equipment which possess the facility should have their self test/self calibration procedures performed. 2 A signal generator should be connected to the existing cabling at the turntable end. The other end of this cable should be connected via a calibrated coaxial cable/10 dB attenuator/adapter/10 dB attenuator/calibrated coaxial cable combination to existing cabling at the other end of the test site. This existing cable should be connected to a receiving device, as illustrated in figure 15 for the case of an Anechoic Chamber. Where the use of a cable is impractical due to the arrangements at the test site, bicones or other suitable antennas could be connected at both ends as appropriate. The signal generator should be scanned across the appropriate frequency range and the response of the receiving device noted. It should be compared with previous tests carried out under similar conditions. Any anomalies should be investigated.
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6.2.3 Standard antennas
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In the frequency band 30 MHz to 1 000 MHz, except where stipulated, both test and substitution/measuring antennas should be tuned half-wavelength dipoles (constructed as detailed in ANSI C63.5 (1988) [11]) aligned for the same polarization. NOTE: Due to size constraints a shortened dipole is used over part of this frequency band. For uniformity of procedures across Open Area Test Sites and both types of Anechoic Chamber, a shortened dipole is used from 30 MHz up to 80 MHz. At all these frequencies the 80 MHz arm length (0,889 m) is used attached to the 20 MHz - 65 MHz balun for all test frequencies from 30 MHz to 65 MHz inclusive or to the 65 MHz - 180 MHz balun for 65 MHz to 80 MHz. Tuned half wavelength dipoles, attached to their matching baluns are used for all frequencies in the band 80 MHz - 1 000 MHz inclusive. Table 2B details dipole arm lengths (as measured from the centre of the balun block) and balun type against frequency. Where the test frequency does not correspond to a set frequency in the table the arm length to be used should be determined by linear interpolation between the closest set values. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 37 Table 2B: Dipole arm length and balun type against frequency Frequency (MHz) Dipole arm length (m) Balun type Frequency (MHz) Dipole arm length (m) Balun type 30 0,889 160 0,440 65 MHz to 35 0,889 180 0,391 180 MHz 40 0,889 20 MHz to 200 0,352 45 0,889 65 MHz 250 0,283 180 MHz to 50 0,889 300 0,235 400 MHz 60 0,889 400 0,175 70 0,889 500 0,143 80 0,889 600 0,117 90 0,791 65 MHz to 700 0,102 400 MHz to 100 0,714 180 MHz 800 0,089 1 000 MHz 120 0,593 900 0,079 140 0,508 1 000 0,076
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6.2.4 Mutual coupling and mismatch loss correction factors
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Correction factors are included where relevant, to allow for mutual coupling and mismatch loss for the 30 MHz to 180 MHz band, based on using the recommended ANSI C63.5 (1988) [11] dipoles. These have been calculated by computer modelling of their baluns, sectional arms and the testing arrangements (i.e. range length, height above ground plane, etc.) using MiniNec. The factors are only valid for this particular type of dipole. However, if this type is unavailable, an alternative could be used. This alternative should be a tuned half wavelength dipole at the particular test frequency. Since correction factors have not been calculated for any type other than the ANSI C63.5 (1988) [11] dipoles this will result in a greater expanded uncertainty for the measurement unless the test house/manufacturer has performed equivalent modelling on the dipoles used.
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6.3 For Stripline test facilities only
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The Stripline to be used is that detailed in CENELEC European Standard EN 55020 [12]. The size of a Stripline limits the usable frequency range. To avoid the possibility of generating unwanted field modes (which can disturb the required electric field distribution in the line), the spacing between the plates should not exceed λ/2 (where λ is the wavelength). The 2-plate Stripline detailed in EN 55020 [12] has a plate spacing of 0,8 m and, consequently, an upper frequency of 150 MHz. Given the further recommendation that, for best accuracy (i.e. closest approximation to a plane wave within the Stripline), an EUT should not measure more than a third of the plate separation, the overall maximum size of EUT which can be accurately tested is dictated as 0,27 m. This size restriction only applies to the vertical dimension within the Stripline, but it is a significant limitation since this is also the direction in which the electric vector points. No other dimension of the EUT should exceed λ/2. These size limitations therefore severely restrict the use of a Stripline. Where larger size EUTs are tested (up to a maximum size in the E-plane of 0,7 m), correction factors need to be applied to the results and significantly greater measurement uncertainty is involved.
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6.3.1 Site preparation
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The Stripline should be placed on non conducting supports at least 0,8 m above the floor and not closer than 0,8 m to the ceiling. When used inside a room (whether screened or not), continuous lines of vertical panels (at least 1 m high) covered in absorbing material should be placed between the open sides of the Stripline and the walls. The absorbing material should provide an adequate level of absorption (typically 15 dB minimum reflectivity at the frequency of test). ETSI ETSI TR 100 027 V1.2.1 (1999-12) 38 At the start of each day, system checks should be made on the Stripline. The following two procedures, as a minimum requirement, should be carried out. 1 All items of test equipment requiring electrical supplies should be connected to their power sources, switched on and allowed adequate time to stabilize, as recommended by the manufacturers. Where a stabilization period is not given by the manufacturer, 30 minutes should be allowed. After this time period, those items of test equipment which possess the facility should have their self test/self calibration procedures performed. Terminating resistor VSWR measuring equipment Figure 16: Stripline test facility set-up for daily checking 2 A VSWR measurement (using for example, a network analyser) should be made on the input to the Stripline, using any necessary coaxial cables and adapters, with the far end of the Stripline terminated in a load (a 150 Ωresistor soldered between the output terminals), as shown in figure 16. No attenuators should be connected between the measuring equipment and the Stripline input. The measurement should cover the full band (30 MHz to 150 MHz). The VSWR measurement should be compared with previous tests and any anomalies investigated.
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6.3.2 Preparation of the EUT
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A block of non-conducting, low dielectric constant (less than 1,5) material should be available, on which the EUT and its bracket can be mounted within the Stripline, so that its volume centre is midway between the plates. The routing of the cables supplying power to the EUT when inside the Stripline should be straight down towards the bottom plate and out of the facility through a small hole in this plate. The cables should be twisted together and loaded with ferrite beads at 0,15 m intervals for their entire lengths within the Stripline. All RF cables used during the test should be dressed with ferrite beads, spaced at 0,15 m intervals, for their entire lengths. They should be routed directly away from the Stripline - the feed cable from the signal generator should be along the line of the Stripline's axis, whilst, during the field measurement part of the test (if carried out), the cable from the Monopole to the receiving device should be at right angles to this axis.
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6.4 For Test Fixtures only
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The Test Fixture should be supplied by the manufacturer of the EUT and should enable testing to be performed under extreme test conditions of temperature and/or voltage, as defined in the relevant standard. It should provide RF connection(s) and allow connection(s) to external power supply(s) and control equipment if necessary. Tests such as adjacent channel power and certain receiver parameters are, for integral antenna devices, usually only performed in a Test Fixture. In these cases the measurement result under normal conditions is directly related to either the effective carrier power (for the case of adjacent channel power testing) or to maximum usable receiver sensitivity (for a receiver parameter) measured on an accredited Free-Field Test Site (i.e. Anechoic Chamber, Anechoic Chamber with a ground plane and Open Area Test Site).
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6.4.1 Site preparation
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For the particular type of EUT, the corresponding results of the verification of the Test Fixture (taken at an accredited Free-Field Test Site) should be available. These results should have been taken under normal conditions in full accordance with the procedures described in the relevant part of ETR 273 [6] and should include the associated measurement uncertainty values. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 39 Test fixtures are always used in conjunction with climatic facilities, within which the RF cabling should be kept as short as possible. The RF cables should be routed by the shortest possible means down to, and out from, the climatic facility. Their entire lengths should also be loaded with ferrite beads spaced 0,15 m apart. The power supply cable(s) should also be as short as possible, twisted together and loaded with ferrite beads spaced 0,15 m apart. At the start of each day, system checks should be made on the test equipment used in the following test methods. The following checking procedures, as a minimum requirement, should be carried out. 1) All items of test equipment requiring electrical supplies should be connected to their power sources, switched on and allowed adequate time to stabilize, as recommended by the manufacturers. Where a stabilization period is not given by the manufacturer, 30 minutes should be allowed. After this time period, those items of test equipment which possess the facility should have their self test/self calibration procedures performed. 2) A network analyser should be connected to the 50 Ωconnector of the Test Fixture and a measurement made of its input VSWR. The measurement should be taken across a frequency band which extends 10 MHz both sides of the nominal frequency of the EUT for which the Test Fixture has been supplied. The results of the test should be compared to previous results. Any anomalies should be investigated.
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6.5 For Salty man/salty-lite testing only
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6.5.1 Range length
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Whichever type of free-field test is used for the tests involving the salty device i.e. Anechoic Chamber, Anechoic Chamber with a ground plane or Open Area Test Site, the range length should be adequate to satisfy the far-field requirements given in subclause 6.2.1.
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6.5.2 Site preparation
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Whichever type of free-field test is used for the tests involving the salty device i.e. Anechoic Chamber, Anechoic Chamber with a ground plane or Open Area Test Site, the site preparation should be carried out in the manner relevant to that Free-Field Test Site (see subclause 6.2.2).
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7 Transmitter measurements
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7.1 Conducted tests
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7.1.1 Frequency error
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7.1.1.1 Definition
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The frequency error of the transmitter is the difference between the unmodulated carrier frequency and the nominal frequency selected for the test.
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7.1.1.2 Method of measurement
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Transmitter under test Frequency meter Test load Figure 17: Measurement arrangement a) The transmitter should be connected to the test load. The carrier frequency should be measured in the absence of modulation. b) The measurement should be repeated under extreme test conditions. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 40
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7.1.2 Carrier power
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7.1.2.1 Definition
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The carrier power is the average power delivered to the test load during one radio frequency cycle in the absence of modulation.
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7.1.2.2 Method of measurement
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Transmitter under test Test load RF power meter Figure 18: Measurement arrangement a) The transmitter should be connected to the test load and the carrier or mean power delivered to this test load measured. b) The value measured should be compared with the rated RF output power. c) The measurement should be repeated under extreme test conditions.
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7.1.3 Adjacent channel power
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7.1.3.1 Definition
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The adjacent channel power is that part of the total power output of a transmitter under defined conditions of modulation, which falls within a specified passband centred on the nominal frequency of either of the adjacent channels. This power is the sum of the mean power produced by the modulation, hum and noise of the transmitter. It is specified either as the ratio expressed in decibels of the carrier power to the adjacent channel power or as an absolute value.
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7.1.3.2 Method of measurement
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Test load Power measuring receiver Modulating signal generator Transmitter under test Figure 19: Measurement arrangement a) The transmitter under test should be connected via the test load to a power measuring receiver calibrated to measure rms power level. The level at the receiver input should be within its allowed limit. The transmitter should be operated at the maximum operational carrier power level. b) With the transmitter unmodulated, the tuning of the power measuring receiver should be adjusted so that a maximum response is obtained. This is the 0 dB response point. The power measuring receiver attenuator setting and the reading of the meter should be recorded. c) The tuning of the power measuring receiver should be adjusted away from the carrier so that its -6 dB response nearest to the transmitter carrier frequency is located at a displacement from the nominal frequency of the carrier as given in table 3. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 41 Table 3: Frequency displacement Channel separation (kHz) Displacement (kHz) 12,5 8,25 20 13 25 17 The same result may be obtained by tuning the power measuring receiver (point D0 in the drawing of the power measuring filter shape) to the nominal frequency of the adjacent channel, if it has been suitably calibrated. d) The transmitter should be modulated as follows: 1) Equipment for analogue speech should be modulated with a 1 250 Hz tone at a level which is 20 dB higher than that required to produce normal deviation. 2) Equipment for data bits should be modulated with the test modulation D-M2 at the agreed deviation. 3) Equipment for messages should be modulated with the test modulation D-M3 repeated continuously at the agreed deviation. e) The power measuring receiver variable attenuator should be adjusted to obtain the same meter reading as in step b) or a known relation to it. This value should be recorded. f) The ratio of adjacent channel power to carrier power is the difference between the attenuator settings in step b) and e), corrected for any differences in the reading of the meter. Alternatively the absolute value of the adjacent channel power may be calculated from the above ratio and the transmitter carrier power. g) Steps c) to f) should be repeated with the power measuring receiver tuned to the other side of the carrier.
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7.1.4 Conducted spurious emissions
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7.1.4.1 Definition
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Conducted spurious emissions are discrete signals whose power is conveyed by conduction to the test load at frequencies other than those of the carrier and sidebands resulting from the normal process of modulation. They are specified as the power level of any discrete signal delivered into a test load.
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7.1.4.2 Method of measurement
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Filter Spectrum analyser or selective voltmeter Test load signal generator Transmitter under test Figure 20: Measurement arrangement a) The transmitter should be connected to a spectrum analyser or a selective voltmeter through a test load and an appropriate filter to avoid overloading of the spectrum analyzer or selective voltmeter. The bandwidth of the spectrum analyser or selective voltmeter should be between 10 kHz and 100 kHz. The equipment used should have sufficient dynamic range and sensitivity to achieve the required measurement accuracy at the specified limit. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 42 For the measurement of spurious emissions below the second harmonic of the carrier frequency the filter used should be a high "Q" (notch) filter centred on the transmitter carrier frequency and attenuating this signal by at least 30 dB. For the measurement of spurious emissions at and above the second harmonic of the carrier frequency the filter used should be a high pass filter with a stop band rejection exceeding 40 dB. The cut-off frequency of the high pass filter should be approximately 1,5 times the transmitter carrier frequency. Precautions may be required to ensure that the test load does not generate or that the high pass filter does not attenuate, the harmonics of the carrier. b) The transmitter should be unmodulated and operating at the maximum limit of its specified power range. c) The frequency of the spectrum analyser or selective voltmeter should be adjusted over the specified frequency range. The frequency and level of every spurious emission found should be noted. The emissions within the channel occupied by the transmitter carrier and its adjacent channels should not be recorded. d) If the spectrum analyser or selective voltmeter has not been calibrated in terms of power level at the transmitter output, the level of any detected components should be determined by replacing the transmitter by the signal generator and adjusting it to reproduce the frequency and level of every spurious emission recorded in step c). e) The absolute power level of each of the emissions noted should be measured and recorded. f) The measurement should be repeated with the transmitter in stand-by condition if this option is available.
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7.1.5 Intermodulation attenuation
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7.1.5.1 Definition
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For the purpose of this test the intermodulation attenuation is a measure of the capability of a transmitter to inhibit the generation of signals in its non-linear elements caused by the presence of the carrier and an interfering signal entering the transmitter via its antenna. It is specified as the ratio, in decibels, of the power level of the third order intermodulation product to the carrier power level.
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7.1.5.2 Method of measurement
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Transmitter under test 10 dB Attenuator 20 dB Attenuator Directional coupler Interfering test signal source Attenuator Termination Spectrum analyser Figure 21: Measurement arrangement a) Preliminary to the measurement the carrier power of the transmitter under test should be measured according to subclause 7.1.2, under normal conditions only, and the value recorded. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 43 The transmitter should be connected to a 50 Ω10 dB power attenuator load and via a directional coupler to a spectrum analyser. An attenuator may be required to avoid overloading the spectrum analyser. The length of the cable between the transmitter under test and the 10 dB power attenuator should be kept to a minimum. The directional coupler should have an insertion loss of less than 1 dB, a sufficient bandwidth, and a directivity of more than 20 dB. The test signal source may be a signal generator and a power amplifier or another transmitter, the output power of which is adjustable. The transmitter under test and the test signal source should be physically separated in such a way that the measurement is not influenced by direct radiation. b) Replace the transmitter under test in the measurement arrangement above by a RF power meter. c) The test signal source should be unmodulated and the frequency should be within 50 kHz to 100 kHz above the frequency of the transmitter under test. The frequency should be chosen in such a way that the intermodulation components to be measured do not coincide with other spurious emissions. d) The test signal power level should be adjusted to -30 dB, relative to the carrier power level recorded above, measured on the RF power meter. e) The transmitter under test should be reconnected to the 10 dB power attenuator, as shown above. f) The transmitter should be unmodulated and the spectrum analyser adjusted to give a maximum indication with a frequency scan width of 500 kHz. g) The intermodulation components should be measured by direct observation on the spectrum analyser and the ratio of the largest third order intermodulation component to the carrier recorded which is situated at the same frequency offset (within 50 kHz to 100 kHz) selected in step c), below the transmitter frequency. h) This measurement should be repeated with the test signal at a frequency within 50 kHz to 100 kHz below the transmitter frequency. In this case the largest third order intermodulation component to be observed in step g) is situated at the same frequency offset selected in step c), above the transmitter frequency.
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7.1.6 Attack time
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7.1.6.1 Definition
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The transmitter attack time is the time interval between the instant at which the final irrevocable logic decision to power up the transmitter is taken and the moment after which: a) the unmodulated transmitter power always remains within a level -1 dB and +1,5 dB of the steady state carrier power; or b) the frequency of the carrier always remains within ±1 kHz from its steady state frequency. NOTE: This may be used for checking the channel efficiency of systems and for defining the timings in protocols. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 44
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100 027
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7.1.6.2 Method of measurement
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Transmitter under test Signal generator Test load Trigger device RF detector or spectrum analyser Test discriminator Storage oscilloscope Figure 22: Measurement arrangement a) The transmitter is connected to a RF detector and to a test discriminator via a matched test load. The attenuation of the test load should be chosen in such a way that the input of the test discriminator is protected against overload and the limiter amplifier of the test discriminator operates correctly in the limiting range as soon as the transmitter carrier power (before attenuation) exceeds 1 mW. A dual trace storage oscilloscope (or a transient recorder) records the amplitude transient from the detector on a logarithmic scale and the frequency transient from the discriminator. A trigger device may be required to ensure that the start of the sweep of the oscilloscope timebase occurs the instant at which the final irrevocable logic decision to power up the transmitter is taken. b) The traces of the oscilloscope should be calibrated in power and frequency (Y axes) and in time (X axis), using the signal generator. c) The transmitter attack time should be measured by direct reading on the oscilloscope.
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100 027
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7.1.7 Release time
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100 027
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7.1.7.1 Definition
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The transmitter release time is the time interval between the instant at which the final irrevocable logic decision to power down the transmitter is taken and the moment when the unmodulated transmitter power has decayed to a level 50 dB below the rated RF output power. NOTE: This may be used for checking the channel efficiency of systems and for defining the timings in protocols.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.7.2 Method of measurement
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Transmitter under test Signal generator Test load Trigger device RF detector or spectrum analyser Storage oscilloscope Figure 23: Measurement arrangement ETSI ETSI TR 100 027 V1.2.1 (1999-12) 45 a) The transmitter is connected to a RF detector via a matched test load. A storage oscilloscope (or a transient recorder) records the amplitude transients from the detector on a logarithmic scale (dynamic range ≥50 dB). A trigger device may be required to start the sweep of the oscilloscope the instant at which the final irrevocable decision to power down the transmitter is taken. If the transmitter possesses an automatic powering down facility (e.g. in the case of fixed length messages transmission), it will replace the trigger device for starting the sweep of the oscilloscope. b) The traces of the oscilloscope should be calibrated in power (Y axis) and in time (X axis) by replacing the transmitter and test load by the signal generator. c) The transmitter release time should be measured by direct reading on the oscilloscope.
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100 027
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7.1.8 Transient adjacent channel power
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7.1.8.1 Definition
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The transient adjacent channel power of a transmitter is expressed as the ratio in decibels of the peak power in the adjacent channels, during the rise or decay time, to the unmodulated carrier power.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.8.2 Method of measurement
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This method of measurement uses a power measuring receiver in the adjacent channels. It should be preceded by two preliminary verifications, in order to guarantee that the transients will not appear outside either of the channels adjacent to the carrier and therefore the measurement should be made in the first adjacent channels next to the carrier only. 7.1.8.2.1 Preliminary verification N°1 This verification has to be made when the transmitter is turned on and off. It uses in both cases the measuring arrangement described for the transmitter "attack time". While the carrier power is greater than 1 mW the instantaneous frequency of the carrier should remain within the tolerance of ±df1, where df1 is the channel separation. 7.1.8.2.2 Preliminary verification N°2 This verification uses the measuring arrangement described for the transmitter "attack time" and transmitter "release time". The rise and decay time measured as the time elapsed between the -30 dB and the -6 dB relative to the steady state carrier power should be greater than 0,2 ms. In addition the shape of the slopes during the rise and decay time should not exhibit abrupt changes in level or parasitic oscillation.
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100 027
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7.1.8.2.3 Measurement
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For application of this method it should be noted that, at the present date no power measurement receivers are available on the market giving sufficient accuracy in the case of short transmission times. Transmitter under test Test load Power measuring receiver Figure 24: Measurement arrangement a) The transmitter under test should be connected via the test load to a power measuring receiver calibrated to measure peak power level. The level at the receiver input should be within its allowed limit. The transmitter should be operated unmodulated at the maximum carrier power level under normal test conditions. b) The tuning of the power measuring receiver should be adjusted so that a maximum response is obtained. This is the 0 dB response point. The receiver attenuator setting and the reading of the meter should be recorded and the transmitter switched off. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 46 c) The tuning of the power measuring receiver should be adjusted away from the carrier so that its -6 dB response nearest to the transmitter carrier frequency is located at a displacement from the nominal frequency of the carrier as given in table 4. Table 4: Frequency displacement Channel separation (kHz) Displacement (kHz) 12,5 8,25 20 13 25 17 The same result may be obtained by tuning the power measuring receiver (point D0 in the drawing of the power measuring filter shape) to the nominal frequency of the adjacent channel, if it has been suitably calibrated. d) The transmitter should be switched on and off once. The receiver variable attenuator should be adjusted to obtain, with the peak transient power, the same level as in step b) or a known relation to it. This value should be recorded. e) The ratio of adjacent channel peak power to carrier power is the difference between the attenuator settings in steps b) and d), corrected for any differences in the reading of the meter. f) Steps c) to e) should be repeated with the power measuring receiver tuned to the other side of the carrier.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.9 Frequency deviation
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100 027
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7.1.9.1 Definition
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The frequency deviation is the maximum difference between the instantaneous frequency of the frequency or phase modulated radio frequency signal and the carrier frequency in the absence of modulation.
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100 027
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7.1.9.2 Method of measurement
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Transmitter under test Test load Deviation meter Modulating signal generator Figure 25: Measurement arrangement The transmitter should be connected to the test load. The frequency deviation should be measured by means of a deviation meter capable of measuring the maximum permissible frequency deviation, including that due to any harmonics and intermodulation products which may be produced in the transmitter. The deviation meter bandwidth should be suitable to accommodate the highest modulating frequency and to achieve the required dynamic range.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.9.2.1 Analogue signals within the audio bandwidth
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a) The modulation frequency should be varied between 300 Hz and the upper specified audio frequency limit. The level of this test signal should be 20 dB above the level corresponding to a deviation at 1 000 Hz of 12 % of the channel separation. b) The maximum (positive or negative) frequency deviation should be recorded. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 47
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100 027
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7.1.9.2.2 Analogue signals above the audio bandwidth
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a) The modulation frequency should be varied between the upper specified audio frequency limit and a frequency equal to the channel separation for which the equipment is intended. The level of this signal should correspond to a deviation at 1 000 Hz of 12 % of the channel separation. b) The maximum (positive or negative) frequency deviation should be recorded.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.9.2.3 Digital signals
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For indirect modulation where the digital signal may either phase or frequency modulate an audio frequency sub-carrier which then modulates the radio frequency carrier the following method should be used. a) The transmitter should be modulated with the test modulation D-M0 at the normal deviation level. b) The maximum (positive or negative) frequency deviation should be recorded. c) The transmitter should be modulated with the test modulation D-M1 at the normal deviation level. d) The maximum (positive or negative) frequency deviation should be recorded. NOTE: Other types of digital modulation will require an alternative method.
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100 027
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7.1.10 Limiter characteristic for analogue speech
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7.1.10.1 Definition
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The limiter characteristic expresses the capability of the transmitter to be modulated with a frequency deviation approaching the maximum permissible frequency deviation.
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100 027
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7.1.10.2 Method of measurement
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Transmitter under test Test load Deviation meter Modulating signal generator Figure 26: Measurement arrangement a) The transmitter under test should be connected via the test load to the deviation meter. b) A modulating signal at a frequency of 1 000 Hz should be applied to the transmitter. The level should be adjusted to produce a frequency deviation of 20 % of the maximum permissible frequency deviation. c) The level should be raised 20 dB and the deviation recorded. d) The measurement should be repeated under extreme test conditions.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.11 Acoustic sensitivity of modulator for analogue speech
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100 027
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7.1.11.1 Definition
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The acoustic sensitivity of the modulator is the capability of the transmitter to be modulated satisfactorily when an audio frequency signal corresponding to the normal average speech level is applied to the microphone. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 48
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100 027
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7.1.11.2 Method of measurement
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Transmitter under test Test load Deviation meter Modulating signal generator Microphone Loudspeaker Figure 27: Measurement arrangement The use of an anechoic acoustic chamber is recommended. Great care should be taken with the acoustic interface to ensure that background noise is minimized and that the correct loudness level is applied to the microphone. a) The transmitter under test should be connected via the test load to the deviation meter. b) An audio frequency signal of 1 000 Hz should be applied to the microphone. The level should be adjusted to produce a frequency deviation of 20 % of the maximum permissible frequency deviation. c) The loudness level at the diaphragm of the microphone should be recorded.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.12 Audio frequency response for analogue speech
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100 027
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7.1.12.1 Definition
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The audio frequency response is the variation of the transmitter frequency deviation as a function of the modulating frequency.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.12.2 Method of measurement
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Transmitter under test Test load Deviation meter Modulating signal generator Figure 28: Measurement arrangement a) The transmitter under test should be connected via the test load to the deviation meter. b) A modulating signal with a frequency of 1 000 Hz should be applied to the transmitter. The level should be adjusted to produce a frequency deviation of 20 % of the maximum permissible frequency deviation. c) The modulating frequency should be varied between 300 Hz and its upper audio frequency limit. The level of the modulating signal should remain constant. d) The variation of the deviation should be recorded at suitable intervals of input frequency. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 49
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100 027
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7.1.13 Harmonic distortion for analogue speech
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100 027
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7.1.13.1 Definition
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The harmonic distortion of a transmitter when modulated with an audio frequency signal is defined as the ratio, expressed as a percentage, of the rms voltage of all the harmonic components of the fundamental audio frequency to the total rms voltage of the signal after linear demodulation.
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100 027
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7.1.13.2 Method of measurement
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Transmitter under test Test load Deviation meter and demodulator Modulating signal generator (De-emphasis filter and) distortion meter Figure 29: Measurement arrangement a) The transmitter under test should be connected via the test load to the deviation meter which has a linear audio output. The output of the deviation meter demodulator should be connected to the distortion meter through a 6 dB/octave de-emphasis filter when the transmitter is phase modulated. If the transmitter is frequency modulated then no filter is required. b) For phase modulation the transmitter should be modulated successively at frequencies of 300 Hz, 500 Hz and 1 000 Hz maintaining a constant modulation index (i.e. keeping the ratio of frequency deviation to the modulating frequency constant). This is the index which produces 60 % of the maximum permissible frequency deviation when modulated at 1 000 Hz. For frequency modulation the transmitter should be modulated successively at frequencies of 300 Hz, 500 Hz and 1 000 Hz with a frequency deviation equal to 60 % of the maximum permissible frequency deviation. c) The harmonic distortion should be recorded at each of the frequencies. d) The measurement should be repeated under extreme test conditions with the modulating signal at 1 000 Hz and the frequency deviation equal to 70 % of the maximum permissible frequency deviation.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.1.14 Residual modulation for analogue speech
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100 027
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7.1.14.1 Definition
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The residual modulation of a transmitter is the ratio, expressed in decibels, of the audio frequency output power produced after the demodulation of the radio frequency signal in the absence of wanted modulation to the audio frequency output power produced by the application of specified test modulation. ETSI ETSI TR 100 027 V1.2.1 (1999-12) 50
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100 027
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7.1.14.2 Method of measurement
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Transmitter under test Test load Deviation meter and demodulator Modulating signal generator (De-emphasis filter and) psophometric filter and rms voltmeter Figure 30: Measurement arrangement Care should be taken to avoid false results caused by the emphasis of low frequency noise in the demodulator. a) The transmitter under test should be connected via the test load to the deviation meter which has a linear audio output. The output of the deviation meter demodulator should be connected to the rms voltmeter through a 6 dB/octave de-emphasis filter and via the psophometric weighting network when the transmitter is phase modulated. If the transmitter is frequency modulated then the de-emphasis filter is not required. b) Test modulation A-M1 should be applied to the transmitter and the level on the rms voltmeter recorded. c) The modulation should be removed and the new level recorded. d) The residual modulation is the ratio, expressed in dB, of the value recorded in step c) to the value recorded in step b).
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100 027
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7.2 Radiated tests
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7.2.1 Frequency error (30 MHz to 1 000 MHz)
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Definition The frequency error of a transmitter is the difference between the measured carrier frequency in the absence of modulation and the nominal frequency of the transmitter as stated by the manufacturer.
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100 027
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7.2.1.1 Anechoic Chamber
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100 027
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7.2.1.1.1 Apparatus required
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- Digital voltmeter; - Ferrite beads; - 10 dB attenuators; - Power supply; - Connecting cables; - Anechoic Chamber; - Test antenna (a half wavelength dipole, bicone or LPDA); - Frequency counter. The type and serial numbers of all items of test equipment should be recorded in the log book results sheet (table 18). ETSI ETSI TR 100 027 V1.2.1 (1999-12) 51 NOTE: The half wavelength dipole antennas, incorporating matching/transforming baluns, for the procedure are available in the following bands: 20 MHz - 65 MHz, 65 MHz - 180 MHz, 180 MHz - 400 MHz, 400 MHz - 1 000 MHz. Constructional details are contained in ANSI C63.5 (1988) [11]. In the recommended antenna scheme for this band, a shortened dipole is used at all frequencies from 30 MHz up to 80 MHz.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.2.1.1.2 Method of measurement
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1) The measurement should always be performed in the absence of modulation. 2) The EUT should be mounted on the turntable, whose surface is at the height specified in the relevant standard or, where not stated, at a convenient height within the "quiet zone" of the Anechoic Chamber. The EUT should be mounted in an orientation which matches that of its normal usage as stated by the manufacturer. This orientation and mounting configuration should be recorded on page 1 of the log book results sheet (table 5). NOTE 1: The turntable should be constructed from non-conducting, low relative dielectric constant (preferably less than 1,5) material(s). 3) The test antenna (dipole, bicone or LPDA) should be oriented for the stated polarization of the EUT. For cases in which the test antenna is a tuned half wavelength dipole, this should be tuned to the appropriate frequency. The output of the test antenna should be connected to the frequency counter via a 10 dB attenuator and the calibrated, ferrited coaxial cable associated with that end of the chamber (see figure 31). The phase centre of the test antenna should be at the same height above the floor as the mid point of the EUT. NOTE 2: Where a dipole is used, frequencies below 80 MHz require a shortened version (as defined in subclause 6.2.3) to be used. For any frequency, the dipole arm length (given in table 2B) is defined from the centre of the balun block to the tip of the arm. From a fully extended state, each telescopic element, in turn, should be "pushed in" from the tip until the required length is obtained. The outermost section should fully compress before any of the others, and so on. Table 2B) also gives the choice of balun for set frequencies. Where the test frequency does not correspond to a set frequency in the table, the arm length to be used should be determined by linear interpolation between the closest set values. Range length 3 m or 10 m Turntable Test antenna EUT entral axis f chamber Quiet zone 10 dB attenuator Frequency counter Power supply unit Digital voltmeter Radio absorbing material Figure 31: Anechoic Chamber set-up for the Frequency error test ETSI ETSI TR 100 027 V1.2.1 (1999-12) 52 4) The EUT should be switched on without modulation, allowed adequate time to stabilize and the resolution of the frequency counter adjusted to read to the nearest Hz. 5) The value of the frequency displayed on the counter should be recorded in the log book results sheet (table 5). NOTE 3: In cases where the frequency does not appear stable, this might require observations over a 30 second or 1 minute time period, noting the highest and lowest readings and estimating the average value. In these cases it is the average value that should be recorded in the log book results sheet (table 5).
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f968701d34274f489f6c9983c6c42197
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100 027
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7.2.1.1.3 Procedure for completion of the results sheets
|
There are two values that need to be derived before the overall results sheet (table 6) can be completed. Firstly the value for frequency error (from a straightforward calculation of recorded frequency minus the nominal frequency) and secondly, the value of the expanded uncertainty for the test. This should be carried out in accordance with TR 100 028-2 [7], subclause 7.2.1.1.
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f968701d34274f489f6c9983c6c42197
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100 027
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7.2.1.1.4 Log book entries
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Table 5: Log book results sheet FREQUENCY ERROR Date: PAGE 1 of 1 Temperature:........................... °°°°C Humidity:.........................% Frequency:.................MHz Manufacturer of EUT: ............. Type No: .......................... Serial No: ................... Range length:.......................... Test equipment item Type No. Serial No. VSWR Insertion loss Antenna factor/gain Test antenna N/A Test antenna attenuator N/A Test antenna cable N/A Digital voltmeter N/A N/A N/A Power supply N/A N/A N/A Ferrite beads N/A N/A N/A Frequency counter N/A N/A Mounting configuration of EUT Reading on frequency counter: Hz
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f968701d34274f489f6c9983c6c42197
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100 027
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7.2.1.1.5 Statement of results
|
The results should be presented in tabular form as shown in table 6. Table 6: Overall results sheet FREQUENCY ERROR Date: PAGE 1 of 1 Frequency error Hz Expanded uncertainty (95 %) Hz ETSI ETSI TR 100 027 V1.2.1 (1999-12) 53
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f968701d34274f489f6c9983c6c42197
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100 027
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7.2.1.2 Anechoic Chamber with a ground plane
|
For Frequency Error testing in an Anechoic Chamber with a ground plane reference should be made to the Open Area Test Site test method (subclause 7.2.1.3), since the procedures are identical. The test equipment and EUT set-up for this test is shown in figure 32. Range length 3 m or 10 m Turntable Test antenna 1 - 4 m EUT 10 dB attenuator Frequency counter Digital voltmeter Ground plane Reflected path Direct path Radio absorbing material Power supply unit Figure 32: Anechoic Chamber with a ground plane set-up for the Frequency error test To complete the overall results sheet for this test, the value for expanded measurement uncertainty should be calculated according to TR 100 028-2 [7], subclause 7.2.1.2.
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f968701d34274f489f6c9983c6c42197
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100 027
|
7.2.1.3 Open Area Test Site
| |
f968701d34274f489f6c9983c6c42197
|
100 027
|
7.2.1.3.1 Apparatus required
|
- Digital voltmeter; - Ferrite beads; - 10 dB attenuators; - Power supply; - Connecting cables; - Open Area Test Site; - Test antenna (a half wavelength dipole, bicone or a LPDA); - Frequency counter. The type and serial numbers of all items of test equipment should be recorded in the log book results sheet (table 7). ETSI ETSI TR 100 027 V1.2.1 (1999-12) 54 NOTE: The half wavelength dipole antennas, incorporating matching/transforming baluns, for the procedure are available in the following bands: 20 MHz - 65 MHz, 65 MHz - 180 MHz, 180 MHz - 400 MHz, 400 MHz - 1 000 MHz. Constructional details are contained in ANSI C63.5 (1988) [11]. In the recommended antenna scheme for this band, a shortened dipole is used at all frequencies from 30 MHz up to 80 MHz.
|
f968701d34274f489f6c9983c6c42197
|
100 027
|
7.2.1.3.2 Method of measurement
|
1 The measurement should always be performed in the absence of modulation. 2 The EUT should be mounted on a turntable whose mounting surface is at the height (above the ground plane) specified in the relevant standard. The EUT should be mounted in an orientation which matches that of its normal usage as stated by the manufacturer. This orientation and mounting configuration should be recorded in the log book results sheet (table 7). NOTE 1: The turntable should be constructed from non-conducting, low relative dielectric constant (preferably less than 1,5) material(s). 3 The test antenna (dipole, bicone or LPDA) should be mounted on the antenna mast and oriented for the stated polarization of the EUT. For cases in which the test antenna is a tuned half wavelength dipole, this should be tuned to the nominal frequency. The output of the test antenna should be connected to the frequency counter via a 10 dB attenuator and the calibrated, ferrited coaxial cable associated with that end of the test site (see figure 33). The phase centre of the test antenna should be at the same height above the floor as the mid point of the EUT. NOTE 2: Where a dipole is used, frequencies below 80 MHz require a shortened version (as defined in subclause 6.2.3) to be used. For any frequency, the dipole arm length (given in table 2B) is defined from the centre of the balun block to the tip of the arm. From a fully extended state, each telescopic element, in turn, should be "pushed in" from the tip until the required length is obtained. The outermost section should fully compress before any of the others, and so on. Table 2B) also gives the choice of balun for set frequencies. Where the test frequency does not correspond to a set frequency in the table, the arm length to be used should be determined by linear interpolation between the closest set values. Test antenna Turntable Power supply unit Digital voltmeter Receiving device EUT 10 dB attenuator Direct path Range length 3 m or 10 m Reflected path 1 m to 4 m Figure 33: Open Area Test Site set-up for the Frequency error test 4 The EUT should be switched on without modulation, allowed adequate time to stabilize and the resolution of the frequency counter adjusted to read to the nearest Hz. 5 For cases in which no reading is given on the frequency counter, the height of the test antenna on the mast should be varied until a reading does appear. 6 The value of the frequency displayed on the counter should be recorded in the log book results sheet (table 7). ETSI ETSI TR 100 027 V1.2.1 (1999-12) 55 NOTE 3: In cases where the frequency does not appear stable, this might require observations over a 30 second or 1 minute time period, noting the highest and lowest readings and estimating the average value. In these cases it is the average value that should be recorded in the log book results sheet (table 7).
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