Subset (3)

documents · 50.6k rows

Split (1)

train · 50.6k rows

chunk_id stringlengths 3 8	chunk stringlengths 1 1k
1922_10	In any case, regardless of its placement, an ATU does not alter the gain, efficiency, or directivity of the antenna, nor does it change the internal complex impedances within the parts of the antenna itself, nor the impedance presented at the antenna’s feedpoint.
1922_11	Efficiency and SWR If there is still a high standing wave ratio (SWR) beyond the ATU, in a significantly long segment of feedline, any loss in that part of the feedline is typically increased by the transmitted waves reflecting back and forth between the tuner and the antenna, causing resistive losses in the wires and possibly the insulation of the transmission line. Even with a matching unit at both ends of the feedline – the near ATU matching the transmitter to the feedline and the remote ATU matching the feedline to the antenna – losses in the circuitry of the two ATUs will slightly reduce power delivered to the antenna. The most efficient use of a transmitter's power is to use a resonant antenna, fed with a matched-impedance feedline to a matched-impedance transmitter; there are still small losses in any feedline even when all impedances match, but matching minimizes loss.
1922_12	It is almost equally efficient to feed a remote antenna tuner attached directly to the antenna, via a feedline matched to the transmitter and the ATU feed; the only extra losses are in the tuner circuitry, which can be kept small if the tuner is correctly adjusted and the line carefully tested at or near the antenna. It is usually inefficient to operate an antenna far from one of its resonant frequencies and attempt to compensate with an ATU next to the transmitter, far from the antenna; the entire feedline from the ATU to the antenna is still mismatched, which will aggravate normal loss in the feedline, particularly if it is low-impedance line, like standard 50 Ω coax. The least efficient way to transmit, is to feed a non-resonant antenna through lossy feedline with no impedance matching anywhere along the line.
1922_13	Use in receivers ATUs are not widely used in shortwave receivers, and almost never used in mediumwave or longwave receivers. They are, however, needed for receivers operating in the upper shortwave (upper HF), and VHF and above.
1922_14	In a receiver, if the complex impedance of the antenna is not a conjugate match for the complex input impedance at the antenna end of the transmission line, then some of the incoming signal power will be reflected back out to the antenna and will not reach the receiver. However this is only important for frequencies at and above the middle HF band. In radio receivers working below roughly 10~20 MHz, atmospheric radio noise dominates the signal to noise ratio (SNR) of the incoming radio signal, and the power of the atmospheric noise that arrives with the signal is far greater than the inherent thermal radio noise generated within the receiver's own circuitry. Therefore, the receiver can amplify the weak signal to compensate for any inefficiency caused by impedance mismatch without perceptibly increasing noise in the output.
1922_15	At higher frequencies, however, receivers encounter very little atmospheric noise and noise added by the receiver's own front end amplifier dominates the signal to noise ratio. At frequencies above about 10~20 MHz the internal circuit noise is the factor limiting sensitivity of the receiver for weak signals, and so as the frequency rises it becomes increasingly important that the antenna complex impedance be conjugately matched to the input impedance at the antenna end of the transmission line, to transfer the maximum available power from a weak signal into the first amplifier to provide a stronger signal than its own internally-generated noise. So impedance-matching circuits or impedance-matched antennas are incorporated in some receivers for the upper HF band, such as ‘deluxe’ CB radio receivers, and for most VHF and higher frequency receivers, such as FM broadcast receivers, and scanners for aircraft and public safety radio.
1922_16	Broad band matching methods Transformers, autotransformers, and baluns are sometimes incorporated into the design of narrow band antenna tuners and antenna cabling connections. They will all usually have little effect on the resonant frequency of either the antenna or the narrow band transmitter circuits, but can widen the range of impedances that the antenna tuner can match, and/or convert between balanced and unbalanced cabling where needed. Ferrite transformers Solid-state power amplifiers operating from 1–30 MHz typically use one or more wideband transformers wound on ferrite cores. MOSFETs and bipolar junction transistors typically used in modern radio frequency amplifiers are designed to operate into a low impedance, so the transformer primary typically has a single turn, while the 50 Ω secondary will have 2 to 4 turns. This design of feedline system has the advantage of reducing the retuning required when the operating frequency is changed.
1922_17	A similar design can match an antenna to a transmission line: For example, many TV antennas have a 300 Ω impedance but feed the signal to the TV through a 75 Ω coaxial line. A small ferrite core transformer makes the broad band impedance transformation. This transformer does not need, nor is it capable of adjustment. For receive-only use in a TV the small SWR variation with frequency is not a major problem. Also note that many ferrite transformers perform a balanced-to-unbalanced transformation in addition to the impedance change. When the anced to balanced function is present these transformers are called a balun (otherwise an unun). The most common baluns have either a 1:1 or a 1:4 impedance transformation.
1922_18	Autotransformers There are several designs for impedance matching using an autotransformer, which is a simple, single-wire transformer with different connection points or taps spaced along the coil windings. They are distinguished mainly by their impedance transform ratio, and whether the input and output sides share a common ground, or are matched from a cable that is grounded on one side (unbalanced) to an ungrounded (usually balanced) cable. When autotransformers connect balanced and unbalanced lines they are called baluns, just as two-winding transformers are.
1922_19	The circuit pictured at the right has three identical windings wrapped in the same direction around either an "air" core (for very high frequencies) or ferrite core (for middle frequencies) or a powdered-iron core (for very low frequencies). The three equal windings shown are wired for a common ground shared by two unbalanced lines (so this design is an unun), and can be used as 1:1, 1:4, or 1:9 impedance match, depending on the tap chosen. For example, if the right-hand side is connected to a resistive load of 10 Ω, the user can attach a source at any of the three ungrounded terminals on the left side of the autotransformer to get a different impedance. Notice that on the left side, the line with more windings between the line's tap-point and the ground tap measures greater impedance for the same 10 Ω load on the right.
1922_20	Narrow band design The "narrow-band" methods described below cover a very much smaller span of frequencies, by comparison with the broadband methods described above. Antenna matching methods that use transformers tend to cover a wide range of frequencies. A single, typical, commercially available balun can cover frequencies from 3.5–30.0 MHz, or nearly the entire shortwave band. Matching to an antenna using a cut segment of transmission line (described below) is perhaps the most efficient of all matching schemes in terms of electrical power, but typically can only cover a range about 3.5–3.7 MHz wide in the HF band – a very small range indeed, compared to the 27 MHz bandwidth of a well-made broadband balun. Antenna coupling or feedline matching circuits are also narrowband for any single setting, but can be re-tuned more conveniently. However they are perhaps the least efficient in terms of power-loss (aside from having no impedance matching at all!).
1922_21	Transmission line antenna tuning methods There are two different impedance matching techniques using sections of feedline: Either the original feedline can have a deliberately mismatched section of line spliced into it (called section matching), or a short stub of line can branch off from the original line, with the stub's end either shorted or left unconnected (called stub matching). In both cases, the location of the section of extra line on the original feedline and its length require careful placement and adjustment, which will almost surely only work for one desired frequency.
1922_22	Section matching A special section of transmission line can be used to match the main line to the antenna, if that line section's characteristic impedance is different from that of the main line. The technique is essentially to fix a mismatch by creating an opposite mismatch: A line segment with the proper impedance and proper length, inserted at the proper distance from the antenna, can perform complicated matching effects with very high efficiency. The drawback is that matching with line segments only works for a very limited frequency range for which the segment's length and position are appropriate.
1922_23	A simple example of this method is the quarter-wave impedance transformer formed by a section of mismatched transmission line. If a quarter-wavelength of 75 Ω coaxial cable is linked to a 50 Ω load, the SWR in the 75 Ω quarter wavelength of line can be calculated as when there is no reactance; the quarter-wavelength of line transforms the mismatched impedance to 112.5 Ω Thus this inserted section matches a 112 Ω antenna to a 50 Ω main line. The wavelength coaxial transformer is a useful way to match 50 to 75 Ω using the same general method. Stub matching A second common method is the use of a stub: Either a shorted or open section of line is connected in parallel with the main feedline, forming a dead-end branch off the main line; with coax this is done using a ‘T’-connector. A stub less than a quarter-wave long whose end is short-circuited acts as an inductor; if its end is left unconnected (open), the stub acts as a capacitor.
1922_24	The length of the stub and its location are chosen so that its susceptance will be equal-and-opposite to the susceptance at that point on the line, and the remaining, non-reactive impedance will match the line below the stub, removing the effects of the complex impedance or SWR from the antenna. The J-pole antenna and the related Zepp antenna are both examples of an antenna with a built-in stub match.
1922_25	Basic lumped circuit matching using the L-network An ‘L’-network is the simplest circuit that will achieve the desired transformation, and always consists of just two components. For any one given antenna and frequency, once a circuit is selected from the eight possible configurations (of which six are shown in the diagram below) only one pair of component values will match the in impedance to the out impedance. Commercially available automatic antenna tuners most often are ‘L’-networks, since they involve the fewest parts and have a unique setting for the adjustment circuitry to seek out. The ‘L’ circuit is important in that many automatic antenna tuners use it, and also because more complicated circuits can be analyzed as chains of ‘L’-networks, as will be seen a later section, in descriptions of more complicated tuners. The basic circuit required when pairs of lumped capacitors and / or inductors are used is shown in the chart of schematics below.
1922_26	This circuit is called an “ell” network, not because it contains an inductor (in fact some ‘L’-networks consist of two capacitors) but rather because in the schematic the two components are at right angles to each other, having the shape (e.g. or ) of a rotated or flipped Roman letter ‘L’. The ‘T’ (“tee”) network and the ‘’ (“pie” / “pee”) network also have their parts laid out in a shape similar to the Roman and Greek letters they are named after. This basic network is able to act as an impedance transformer. If the output has an impedance consisting of resistive part and reactive part load, which add to make a single complex number The input is to be attached to a source which has an impedance of source resistance and reactance, then and . In this example circuit, and can be swapped. All the ATU circuits below create this network, which exists between systems with different impedances.
1922_27	For instance, if the source has a resistive impedance of 50 Ω and the load has a resistive impedance of 1000 Ω : If the frequency is 28 MHz, As, then, So, While as, then, Theory and practice A parallel network, consisting of a resistive element (1000 Ω) and a reactive element (−j 229.415 Ω), will have the same impedance and power factor as a series network consisting of resistive (50 Ω) and reactive elements (−j 217.94 Ω). By adding another element in series (which has a reactive impedance of +j 217.94 Ω), the impedance is 50 Ω (resistive). Types of L-networks and their uses The L-network can have eight different configurations, six of which are shown in the diagrams at the right. The two omitted configurations are the same as the bottom row, but with the parallel element (wires vertical) on the right side of the series element (wires horizontal), instead of on the left, as shown.
1922_28	In discussion of the diagrams that follows the in connector comes from the transmitter or "source" on the left; the out connector goes to the antenna or "load" on the right. Without exception, the horizontal element of an L-network goes in series with the side that has the lowest resistance. So for example, the three circuits in the left column and the two in the bottom row have the series (horizontal) element on the out side are used for stepping up from a low-resistance input (transmitter) to a high-resistance output (antenna), similar to the example analyzed in the section above. The top two circuits in the right column, with the series (horizontal) element on the in side, are generally useful for stepping down from a higher input to a lower output resistance.
1922_29	The rule only applies to the resistive part of the load, not its reactive part, so orienting the network based on a meter that only indicates total impedance and not its separate parts may not be successful. In cases where the load is highly reactive – such as an antenna fed with a signal whose frequency is far away from any resonance – the configuration determined by resistance may be opposite the configuration supposed from the total impedance. If far from resonance, the bottom two step down (high-in to low-out) circuits would be used to connect for a step up of impedance (low-in to high-out that is mostly from reactance, not resistance, rather than the actual high-in to low-out resistance for which the orientation rule truly applies).
1922_30	The low- and high-pass versions of the four circuits shown in the top two rows use only one inductor and one capacitor. Normally, the low-pass would be preferred with a transmitter, in order to attenuate possible harmonics, but the high-pass configuration may be chosen if the components are more conveniently obtained, or if the radio already contains an internal low-pass filter, or if attenuation of low frequencies is desirable – for example when a local AM station broadcasting on a medium frequency may be overloading a high frequency receiver. It is also possible that one or the other of the low-pass or the high-pass networks may have lower enough loss to make it preferred.
1922_31	In the bottom row, the Low R, high C circuit is shown feeding a short vertical antenna, such as would be the case for a compact, mobile antenna or otherwise on frequencies below an antenna's lowest natural resonant frequency. In both cases, small antennas lead to small radiation resistance, so the step-down configuration is appropriate. Here the inherent capacitance of a short, random wire antenna is so high that the L-network is best realized with two inductors, instead of aggravating the problem by using a capacitor. The Low R, high L circuit is shown feeding a small loop antenna. Below resonance this type of antenna has so much inductance, that more inductance from using a coil in the network would make the reactance even worse. Therefore, the L-network is composed of two capacitors.
1922_32	Tuners for unbalanced feedlines In contrast to two-element L-networks, the circuits described below all have three or more components, and hence have many more choices for inductance and capacitance that will produce an impedance match, unfortunately including some bad choices. The two main goals of a good match are: to minimize losses in the matching circuit, and to maximize the span of frequencies that are matched tolerably well. To obtain good matches and avoid bad ones, with every antenna and matching circuit combination, the radio operator must experiment, test, and use judgement to choose among the many adjustments that match the same impedances. This section discusses circuit designs for unbalanced lines; it is followed by a section that discusses tuners for balanced lines. High-pass T-network
1922_33	This configuration is currently popular because it is capable of matching a large impedance range with capacitors in commonly available sizes. However, it is a high-pass filter and will not attenuate spurious radiation above the cutoff frequency nearly as well as other designs (see the -network section, below). Due to its low losses and simplicity, many home-built and commercial manually tuned ATUs use this circuit. The tuning coil is normally also adjustable (not shown). The ‘T’ network shown here may be thought of as a high-pass step-down ‘L’ network on the input side feeding into a high-pass step-up ‘L’ network on the output side (). The two side-by-side inductors in the conjoined circuit are combined into a single equivalent inductor.
1922_34	Theory and practice If a source impedance of 200 Ω and a resistive load of 1000 Ω are connected (via a capacitor with an impedance of −j 200 Ω) to the inductor of the transmatch, vector mathematics can transform this into a parallel network consisting of a resistance of 1040 Ω and a capacitor with an admittance of 1.9231×10−4 siemens (XC = 5200 Ω). A resistive load (RL) of 1000 Ω is in series with XC −j 200 Ω. The phase angle is To convert to an equivalent parallel network If the reactive component is ignored, a 1040 Ω to 200 Ω transformation is needed (according to the equations above, an inductor of +j 507.32 Ω). If the effect of the capacitor (from the parallel network) is taken into account, an inductor of +j 462.23 Ω is needed. The system can then be mathematically transformed into a series network of 199.9 Ω resistive and +j 409.82 Ω reactive. A capacitor (−j 409.82) is needed to complete the network. The steps are shown here. Hover over each circuit for captions.
1922_35	Low-pass network A (pi) network can also be used; it is the electrical conjugate of the ‘T’ network. This ATU has exceptionally good attenuation of harmonics, and was incorporated into the output stage of tube-based ‘vintage’ transmitters and many modern tube-based RF amplifiers. However, the standard circuit is not popular for stand-alone multiband antenna tuners, since the variable capacitors needed for the lower Amateur bands are inconveniently large and expensive. The network shown here may be thought of as a low-pass step-up ‘L’ network on the input side feeding into a low-pass step-down ‘L’ network on the output side (). The two noze-to-noze inductors in the joined circuit are replaced with a single equivalent inductor. Drake’s modified -network
1922_36	A modified version of the -network is more practical as it uses a fixed input capacitor (left), which can be several thousand picofarads, allowing the two variable capacitors to be smaller. A band switch selects an inductor and an input capacitor. This circuit was used in tuners covering 1.8–30 MHz made before the popularity of the simpler ‘T’‑network, above. It can also be viewed as two ‘L’ networks coupled front to back: A capacitor-inductor low pass step-up network on the left, feeding into a capacitor-capacitor step-up network on the right (). SPC tuner The Series Parallel Capacitor or SPC tuner uses a band-pass circuit that can act both as an antenna coupler and as a preselector. Because it is a band-pass circuit, the SPC tuner has much better harmonic suppression than the T-match above, but uses similar-cost tuning capacitors; its performance is better than the "Ultimate" circuit below. The SPC’s harmonic suppression is only surpassed by the -network tuners, described above.
1922_37	The SPC circuit is equivalent to a back-to-back pair of ‘L’ networks: A high-pass capacitor-inductor step down network on the input side feeding into a capacitor-capacitor step up network on the output side (). The combination of the grounded inductor and the grounded capacitor is a tank circuit, that drains to ground out-of-tune signals. When tuned to exploit that action, the tank circuit makes the SPC a band-pass filter that eliminates harmonics as effectively as the network, although requiring more careful adjustment for best results. With the SPC tuner the losses will be somewhat higher than with the ‘T’-network, since the grounded capacitor will shunt some reactive current to ground, which must be cancelled by additional current in the inductor. The trade-off is that the effective inductance of the coil is increased, thus allowing operation at lower frequencies than would otherwise be possible.
1922_38	Ultimate Transmatch Originally, the Ultimate Transmatch was promoted as a way to make the components more manageable at the lowest frequencies of interest and also to get some harmonic attenuation. A version of McCoy's Ultimate Transmatch network is shown in the illustration to the right. It is now considered obsolete; using identical parts, the design goals were better realized by the Series-Parallel Capacitor (SPC) network, shown above, which was designed after the name Ultimate had already been used. It has the same general filter topology () as the Drake modified , above, but with the capacitor-capacitor component on the left, input side, instead of the right, and a high-pass ‘L’-component on the other side instead of a low-pass component.
1922_39	Balanced line tuners Balanced (open line) transmission lines require a tuner that has two "hot" output terminals, rather than one "hot" terminal and one "cold" (grounded). Since all modern transmitters have unbalanced (co-axial) output – almost always 50 Ω – the most efficient system has the tuner provide a balun (balanced to unbalanced) transformation as well as providing an impedance match. The tuner usually includes a coil, and the coil can accept or produce either balanced or unbalanced input or output, depending on where its tap points are placed. Balanced versions of unbalanced tuner circuits All of the unbalanced tuner circuits described in the preceding main section can be converted to an equivalent balanced circuit by a standard procedure.
1922_40	Commercially available "inherantly balanced" tuners are made as balanced versions of L, T, and circuits. Their drawback is that the components used for each of the two output channels must be carefully matched and attached pairs, so that adjusting them causes an identical tuning change to both "hot" sides of the circuit. Hence, most "inherently balanced" tuners are more than twice as expensive as unbalanced tuners. Tuned-transformer balanced circuits The following balanced circuit types have been used for tuners, illustrated in the diagram below. They are all based on tuned transformer circuits; none are balanced versions of the unbalanced circuits discussed above.
1922_41	Optional and mandatory grounding connections All of the circuits show a ground connection (a downward pointing triangle) on the antenna side (right hand side). The antenna ground on the right is shaded grey, with dashed lines, because it is optional; if used it effectively forces balanced voltage against ground on the two output terminals. The triangle on the left represents a mandatory ground, obtained through the signal line ground cabled to the transmitter (although it should be redundantly wired to ground, as shown, for RF safety).
1922_42	Fixed link with taps The Fixed link with taps (top left on the diagram) is the most basic circuit. The factor will be nearly constant and is set by the number of relative turns on the input link. The match is found by tuning the capacitor and selecting taps on the main coil, which may be done with a switch accessing various taps or by physically moving clips from turn to turn. If the turns on the main coil are changed to move to a higher or lower frequency, the link turns should also change.
1922_43	Hairpin tuner The Hairpin tuner (top right) has the same circuit, but uses a “hairpin” inductor (a tapped transmission line, short-circuited at the far end). Moving the taps along the hairpin allows continuous adjustment of the impedance transformation, which is difficult with a solenoid coil. It is useful for very short wavelengths from about 10 meters to 70 cm (frequencies about 30 MHz to 430 MHz) where the solenoid inductor would have too few turns to allow fine adjustment. These tuners typically operate over at most a 2:1 frequency range.
1922_44	Series cap with taps The illustration shows two versions of essentially the same circuit: Series cap with taps and an alternate configuration For low-Z lines. Series cap with taps (middle, left) adds a series capacitor to the input side of the Fixed link with taps. The input capacitor allows fine adjustment with fewer taps on the main coil. An alternate connection (middle, right) for the series cap circuit is useful for low impedances only, but avoids the taps (For low-Z lines in the illustration). Swinging link with taps Swinging link with taps (bottom left). A swinging link inserted into the Fixed link with taps also allows fine adjustment with fewer coil taps. The swinging link is a form of variable transformer, that changes the coils' mutual inductance by swinging the input coil in and out of the gap between halves of the main coil. The variable inductance makes these tuners more flexible than the basic circuit, but at some cost in complexity.
1922_45	Fixed link with differential capacitors Fixed link with differential capacitors (bottom right). The circuit with differential capacitors was the design used for the well-regarded Johnson Matchbox (JMB) tuners. The four output capacitors sections (C2) are a double-differential capacitor: The axes of the four sections are mechanically connected and their plates aligned so that as the top and bottom capacitor sections increase in value the two middle sections decrease in value, and vice versa (notice in the diagram the complementary and opposing directions of the arrow heads on C2). This provides a smooth change of loading that is electrically equivalent to moving taps on the main coil. The Johnson Matchbox used a band switch to change the turns on the main inductor for each of the five frequency bands available to hams in the 1950s. Later, similar designs also have switched taps on the link (input) inductor.
1922_46	The JMB design has been criticized since the two middle-section capacitors in C2 are not strictly necessary to obtain a match; however, the middle sections conveniently limit the disturbance of the adjustment for C1 caused by changes to C2.
1922_47	Z match The Z-Match is an ATU widely used for low-power amateur radio which is commonly used both as an unbalanced and as a balanced tuner. The Z match is a doubled version of a resonant transformer circuit, with three tuning capacitors. Two of the capacitors with separate connections to the primary transformer coil are ganged, and effectively constitute two separate resonant transformer circuits, with two distinct resonant frequencies. The double-resonance enables the single circuit across the coil to cover a wider frequency range without switching the inductance. Because the output side is a transformer secondary (optionally grounded) it can be used to feed either balanced or unbalanced transmission lines, without any modification to the circuit.
1922_48	The Z-match design is limited in its power output by the core used for the output transformer. A powdered iron or ferrite core about 1.6 inches in diameter should handle 100 W. A tuner built for low-power use (“QRP” – typically 5 W or less) can use a smaller core. Note also that all of the capacitors in the design must be electrically isolated from ground. Unbalanced tuner and a balun Another approach to feeding balanced lines is to use an unbalanced tuner with a balun on either the input (transmitter) or output (antenna) side of the tuner. Most often using the popular high pass T circuit described above, with either a 1:1 current balun on the input side of the unbalanced tuner or a balun (typically 4:1) on the output side. It can be managed, but doing so both efficiently and safely is not easy.
1922_49	Balun between the antenna and the ATU Any balun placed on the output (antenna) side of a tuner must be built to withstand high voltage and current stresses, because of the wide range of impedances it must handle. For a wide range of frequencies and impedances it may not be possible to build a robust balun that is adequately efficient. For a narrow range of frequencies, using transmission line stubs or sections for impedance transforms (as described above) may well be more feasible and will certainly be more efficient.
1922_50	Balun between the transmitter and the ATU The demands put on the balun are more modest if the balun is put on the input end of the tuner – between the tuner and the transmitter. Placed on that end it always operates into a constant 50 Ω impedance from the transmitter on one side, and has the matching network to protect it from wild swings in the feedline impedance on the other side: All to the good. Unfortunately, making the input from the transmitter balanced creates problems that must be remedied.
1922_51	If an unbalanced tuner is fed with a balanced line from a balun instead of directly from the transmitter, then its normal antenna connection – the center wire of its output coaxial cable – provides the signal as usual to one side of the antenna. However the ground side of that same output connection must now feed an equal and opposite current to the other side of the antenna, and the entire grounded portion of the tuner becomes "hot" with RF power, including the tuner's metal chassis and control knobs.
1922_52	The "hot ground" in the ATU The "true" external ground voltage at the antenna and transmitter must lie halfway between the two "hot" feeds, one of which is the internal ground: Inside the ATU, the matching circuit's "false" ground level is equally different from the "true" ground level at either the antenna or the transmitter as the original "hot" wire is (but with opposite polarity). Either the "hot" output wire or the matching circuit "ground" will give you exactly the same shock if you touch it. The tuner circuit must "float" above or below the exterior ground level in order for the ATU circuit ground (or common side) to feed the second hot wire that formerly was attached to the output cable's ground wire: The circuit's floating ground must provide a voltage difference adequate to drive current through an output terminal to make the second output "hot".
1922_53	High voltages are normal in any efficient ("high ") impedance matching circuit bridging a wide mismatch. Unless the incompatible grounds are carefully kept separate, the high voltages present between this interior floating ground and the exterior transmitter and antenna grounds can lead to arcing, corona discharge, capacitively coupled ground currents, and electric shock. Carefully keeping the incompatible grounds separate To reduce power loss and protect the operator and the equipment, the tuner chassis must be double-layered: An outer chassis and an inner chassis. The outer chassis must enclose and separate the tuning circuit and its floating ground from the outside, while itself remaining at the level of the exterior ground(s). With the protective outer chassis, the inner chassis can maintain its own incompatible "floating ground" level, safely isolated.
1922_54	The inner chassis can be reduced to nothing more than a mounting platform inside the outer chassis, elevated on insulators to keep a safe distance between the "floating ground" and the "true" electrical ground line(s) wired to the outer chassis. The inner tuning circuit's metal mounting chassis, and in particular the metal rods connected to adjustment knobs on the outer chassis must all be kept separate from the surface touched by the operator and from direct electrical contact with the transmitter's ground on its connection cable ("true" ground).
1922_55	Isolating the controls is usually done by replacing at least part of the metal connecting rods between knobs on the outside surface and adjustable parts on the inside platform with an insulated rod, either made of a sturdy ceramic or a plastic that tolerates high temperatures. Further, the metal inner and outer parts must be spaced adequately far apart to prevent current leaking out via capacitive coupling when the interior voltages are high. Finally, all these arrangements must be secured with greater than usual care, to ensure that jostling, pressure, or heat expansion cannot create a contact between the inner and outer grounds.
1922_56	Summary Using an inherently unbalanced circuit for a balanced tuner puts difficult constraints on the tuner's construction and high demands on the builder's craftsmanship. The advantage of such a design is that its inner, inherently unbalanced matching circuit always requires only a single component where a balanced version of the same circuit often requires two. Hence it does not require identical pairs of components for the two "hot" ends of the circuit(s) in order to ensure balance to ground within the ATU, and its output is inherently balanced with respect to the exterior "true" ground, even though the interior circuit is unbalanced with respect to the interior "false" ground. Antenna system losses
1922_57	ATU location An ATU can be inserted anywhere along the line connecting the radio transmitter or receiver to the antenna. The antenna feedpoint is usually high in the air (for example, a horizontal dipole antenna) or far away (for example, a ground-mounted monopole antenna placed far from radio interference sources, such as house-wiring and the computer sitting beside the transmitter). A transmission line (feedline) must carry the signal between the transmitter and the antenna. The ATU can be placed anywhere along the feedline – at the transmitter output, at the antenna input, or anywhere in between – and if desired, two or more ATUs can be placed at different locations between the antenna and the transmitter (usually at the two ends of the feedline) and tuned so that they co‑operatively create an impedance match throughout the antenna system.
1922_58	Antenna matching is best done as close to the antenna as possible, to minimize loss, increase bandwidth, and reduce voltage and current on the transmission line. Also, when the information being transmitted has frequency components whose wavelength is a significant fraction of the electrical length of the feed line, distortion of the transmitted information will occur if there are standing waves on the line. Analog TV and FM stereo broadcasts are affected in this way; for those modes, placing the matching unit at or very near the antenna is mandatory. When possible, an automatic or remotely-controlled tuner in a weather-proof case at or near the antenna is convenient and makes for an efficient system. With such a tuner, it is possible to match a wide variety of antennas over a broad range of frequencies (including stealth antennas).
1922_59	High-impedance feedline When the ATU must be located near the radio for convenient adjustment, any significant SWR will increase the loss in the feedline. For that reason, when using an ATU at the transmitter, low-loss, high-impedance feedline is a great advantage (open-wire line, for example). High impedance lines – such as most parallel-wire lines – carry power mostly as high voltage rather than high current, and current alone determines the power lost to line resistance. So for the same number of Watts delivered to the antenna, typically very little power is lost in high-impedance line even at severe SWR levels, when compared to losses in low-impedance line, like typical coaxial cable, with the same SWR. A short length of coaxial line with low loss is acceptable, but with longer coaxial lines the greater losses, aggravated by SWR, become very high.
1922_60	It is important to remember that when an ATU is placed near the transmitter and far from the antenna, even though the ATU matches the transmitter to the line there is no change in the line beyond the ATU. The backlash currents reflected from the antenna are retro-reflected by the ATU and so are invisible on the transmitter-side of the ATU. Individual waves are usually reflected between the antenna and the ATU several times; the result of the multiple reflections is compounded loss, higher voltage and / or higher currents on the line and in the ATU, and narrowed bandwidth. None of these bad effects can be remediated by an ATU sitting beside the transmitter. Loss in antenna tuners Every means of impedance match will introduce some power loss. This will vary from a few percent for a transformer with a ferrite core, to 50% or more for a complicated ATU that is improperly adjusted, or working near the limits of its tuning range.
1922_61	Among the narrow-band tuner circuits, the L-network has the lowest loss, partly because it has the fewest components, but mainly because it can match at just one setting, and that setting is necessarily the lowest possible for a given impedance transformation. In effect, the L-network does not have any "bad match" to choose: Its only available match is good.
1922_62	The L-network using only capacitors will have the lowest loss, but this network only works where the load impedance is very inductive, making it a good choice for a small loop antenna. Inductive impedance also occurs with straight-wire antennas used at frequencies slightly above a resonant frequency, where the antenna is too long – for example, between a quarter and a half wave long at the operating frequency – hence, one can deliberately build an antenna that is too long for all design frequencies with the intention of tuning it only with capacitors, similar to a loop antenna. Unfortunately, the typical problem encountered in the HF band is that antennas are too short for the frequency in use, and tuning them requires inductive reactance. With the high-pass T-network, the loss in the tuner can vary from a few percent – if tuned for lowest loss – to over 50% if the tuner is adjusted to a "bad match" instead of a good one.
1922_63	As a rule of thumb, using the maximum possible capacitance will involve the least loss, as compared to simply tuning for any match, without regard for the settings. This is because increasing the capacitance produces less reactance; the usual consequence is that less balancing reactance is needed from the inductor, which means running current through fewer turns of wire on the inductor, and the loss in almost every ATU is mainly from resistance in the inductor wire (loss from dirty capacitor contacts comes in a distant second).
1922_64	Sacrificing efficiency in exchange for harmonic suppression If additional filtering is desired, the inductor in any of the three-element designs can be deliberately set to large values, raising the circuit and so providing a partial band pass effect. Either the high-pass T or low-pass can be adjusted in this manner; the SPC tuner provides a full band-pass effect when similarly adjusted. The additional attenuation at harmonic frequencies can be increased significantly with only a small percentage of additional loss at the tuned frequency. When adjusted for minimum loss, the SPC tuner will always have better harmonic rejection than the high-pass T, since the SPC design is a band-pass circuit. Either type is capable of good harmonic rejection if a small additional loss is acceptable. The low-pass has exceptional harmonic attenuation at any setting, including the lowest-loss. Standing wave ratio
1922_65	It is a common misconception that a high standing wave ratio (SWR) per se causes loss, or that an antenna must be resonant in order to transmit well; neither is true. A well-adjusted ATU feeding an antenna through a low-loss line may have only a small percentage of additional loss compared with an intrinsically matched antenna, even with a high SWR (4:1, for example). An ATU sitting beside the transmitter just re-reflects energy reflected from the antenna (“backlash current”) back yet again along the feedline to the antenna (“retro-reflection”). High losses arise from RF resistance in the feedline and antenna, and those multiple reflections due to high SWR cause feedline losses to be compounded.
1922_66	Using low-loss, high-impedance feedline with an ATU results in very little loss, even with multiple reflections. However, if the feedline-antenna combination is ‘lossy’, like coaxial line, then an identical high SWR may waste a considerable fraction of the transmitter's power output heating up the coax. On the other hand, parallel-wire, high impedance line typically has much lower loss, even when SWR is high. For that reason, radio operators using high-impedance feedline can be more casual about using tuners.
1922_67	Without an ATU, the SWR from a mismatched antenna and feedline can present an improper load to the transmitter, causing distortion and loss of power or efficiency with heating and/or burning of the output stage components. Modern solid state transmitters are designed to automatically protect themselves by reducing power when confronted with backlash current. Consequently, some solid-state power stages only produce weak signals if the SWR rises above 1.5:1 . Were it not for that problem, even the losses from an SWR of 2:1 could be tolerated, since only 11 percent of transmitted power would be reflected and 89 percent sent through to the antenna (a loss of only dB). So the main loss of power at high SWR is due to the transmitter ‘backing off’ its output power when challenged by a high SWR.
1922_68	Tube transmitters and amplifiers usually have an adjustable output network that can feed mismatched loads up to perhaps 3:1 SWR without trouble. In effect the network in the transmitter output stage acts as a built-in ATU. Further, tubes are electrically robust (even though mechanically fragile), so tube-based circuits have no need to ‘back off’ their output power, since they can shrug off very high backlash current with impunity. Broadcast Applications AM broadcast transmitters One of the oldest applications for antenna tuners is in mediumwave and shortwave AM broadcasting transmitters. AM band transmitters usually use a vertical antenna (tower) which are usually between 0.20 and 0.68 wavelengths long. At the base of the tower (in the "coupling hut") an ATU is used to match the antenna to the 50 Ω transmission line from the transmitter. The most commonly used circuit is a low-pass T-network with two series inductors and a shunt capacitor between them.
1922_69	When multiple towers are used the ATU network may also provide for a phase adjustment, so that the currents in each tower can be phased relative to the others to produce a signal in a desired direction. Stations are often required by the terms of their operating license to prevent signals in directions that could produce interference with other stations. The transmitting station also benefits from more of the station's signal power, paid for in its electrical bill, going into its assigned target area, on which its advertising revenue is based. Adjustment of the ATUs in a multitower array is a complicated, time-consuming process, requiring considerable expertise.
1922_70	High-power shortwave transmitters High-power (50 kW and above) international shortwave broadcasting stations change frequencies seasonally – even daily – to adapt to ionospheric propagation conditions, so their signals can reach their intended audience. Frequent transmitting frequency changes require frequent adjustment of antenna matching and phasing circuitry. Modern shortwave transmitters typically include built-in impedance-matching circuitry for SWR up to 2:1 that can adjust to a new frequency and hence new output impedance within 15 seconds.
1922_71	The matching networks in transmitters sometimes incorporate a balun or an external one can be installed at the transmitter in order to feed a balanced line. Through to the 1950s balanced transmission lines of 300 Ω or more were more-or-less standard for all shortwave transmitters and antennas, including amateurs' equipment. Most shortwave broadcasters continue to use high-impedance feeds even after automatic impedance matching has become commonly available.
1922_72	The most commonly used shortwave antennas for international broadcasting are the HRS antenna (curtain array), which covers a 2 to 1 frequency range, and the log-periodic antenna, which can cover up to an 8 to 1 frequency range. Within the design range, the antenna SWR will vary, but these designs usually keep the SWR below 1.7 to 1 – easily within the range of SWR that can be tuned by built-in automatic antenna matching in many modern transmitters. So when feeding well-chosen antennas, a modern transmitter will be able to adjust itself as needed to match to the antenna at any frequency. Automatic Antenna Tuning Automatic antenna tuning is used in flagship mobile phones; in transceivers for amateur radio; and in land mobile, marine, and tactical HF radio transceivers.
1922_73	Several control schemes can be used, in a radio transceiver or radio transmitter, to automatically adjust an antenna tuner (AT). Each AT shown in the figure has a port, referred to as ″antenna port″, which is directly or indirectly coupled to an antenna, and another port, referred to as ″radio port″ (or as ″user port″), for transmitting and/or receiving radio signals through the AT and the antenna. Each AT shown in the figure is a single-antenna-port (SAP) AT, but a multiple-antenna-port (MAP) AT may be needed for MIMO radio transmission.
1922_74	Several control schemes, which can be used to automatically adjust a SAP AT of a wireless transmitter, are based on one of the two configurations shown in the figure. In both configurations, the transmitter comprises: an antenna; the AT; a sensing unit (SU); a control unit (CU); and a transmission and signal processing unit (TSPU) which consists of all parts of the transmitter not shown elsewhere in the figure. The TX port of the TSPU delivers an excitation. The SU delivers, to the TSPU, one or more sensing unit output signals determined by one or more electrical variables (such as voltage, current, incident or forward voltage, etc) caused by the excitation, sensed at the radio port in the case of configuration (a) or at the antenna port in the case of configuration (b).
1922_75	It is possible to define five types of antenna tuner control schemes. Type 0 designates the open-loop AT control schemes which do not use any SU, the adjustment being typically only based on the knowledge of an operating frequency. Type 1 and type 2 control schemes use configuration (a), type 2 using extremum-seeking control whereas type 1 doesn't. Type 3 and type 4 control schemes use configuration (b), type 4 using extremum-seeking control whereas type 3 doesn't. The control schemes may be compared as regards: their use of closed-loop control and/or open-loop control; the measurements used; their ability to mitigate the effects of the electromagnetic characteristics of the surroundings; their aim; their accuracy and speed; and their dependence on a model of the AT and CU. See also Notes References Further reading External links Tuner Wireless tuning and filtering
1923_0	Piers Anthony Dillingham Jacob (born 6 August 1934) is an American author in the science fiction and fantasy genres, publishing under the name Piers Anthony. He is best known for his long-running novel series set in the fictional realm of Xanth. Many of his books have appeared on The New York Times Best Seller list, and he claims one of his greatest achievements has been to publish a book beginning with every letter of the alphabet, from Anthonology to Zombie Lover.
1923_1	Early life Anthony's parents, Alfred and Norma Jacob, were Quaker pacifists studying at Oxford University who interrupted their studies in 1936 to undertake relief work on behalf of the Quakers during the Spanish Civil War, establishing a food kitchen for children in Barcelona. Piers and his sister were left in England in the care of their maternal grandparents and a nanny. Alfred Jacob, although a British citizen, had been born in America near Philadelphia, and in 1940, after being forced out of Spain and with the situation in Britain deteriorating, the family sailed to the United States. In 1941 the family settled in a rustic "back to the land" utopian community near Winhall, Vermont, where a young Piers made the acquaintance of radical author Scott Nearing, a neighbor. Both parents resumed their academic studies, and Alfred eventually became a professor of Romance languages, teaching at a number of colleges in the Philadelphia area.
1923_2	Piers was moved around to a number of schools, eventually enrolling in Goddard College in Vermont where he graduated in 1956. On This American Life on 27 July 2012, Anthony revealed that his parents had divorced, he was bullied, and he had poor grades in school. Anthony referred to his high school as a "very fancy private school", and refuses to donate money to it. He recalls being part of "the lower crust", and that no one paid attention to, or cared about him. He said, "I didn't like being a member of the underclass, of the peons like that".
1923_3	Marriage and early career Anthony met his future wife, Carol Marble, while both were attending college. They were married in 1956, the same year he graduated from Goddard College, and he worked in a series of odd jobs. In 1957, Anthony decided to join the United States Army, as his wife was now pregnant, and they needed both medical coverage and a steady source of income. During his two-year enlistment, he became a naturalized U.S. citizen in 1958 and became an editor and cartoonist for his battalion's newspaper. After completing military service, he briefly taught school at Admiral Farragut Academy in St. Petersburg, Florida before deciding to try to become a full-time writer.
1923_4	Anthony and his wife made a deal: if he could sell a piece of writing within one year, she would continue to work to support him. But if he could not sell anything in that year, then he would forever give up his dream of being a writer. At the end of the year, he managed to get a short story published. He credits his wife as the person who made his writing career possible, and he advises aspiring writers that they need to have a source of income other than their writing in order to get through the early years of a writing career.
1923_5	Writing On multiple occasions Anthony has moved from one publisher to another (taking a profitable hit series with him) when he says he felt the editors were unduly tampering with his work. He has sued publishers for accounting malfeasance and won judgments in his favor. Anthony maintains an Internet Publishers Survey in the interest of helping aspiring writers. For this service, he won the 2003 "Friend of EPIC" award for service to the electronic publishing community. His website won the Special Recognition for Service to Writers award from Preditors and Editors, an author's guide to publishers and writing services. His popular novel series Xanth has been optioned for movies. It inspired the DOS video game Companions of Xanth, by Legend Entertainment. The same series also spawned the board game Xanth by Mayfair Games.
1923_6	Anthony's novels usually end with a chapter-long Author's Note, in which he talks about himself, his life, and his experiences as they related to the process of writing the novel. He often discusses correspondence with readers and any real-world issues that influenced the novel. Since about 2000, Anthony has written his novels in a Linux environment. Anthony's Xanth series was ranked No. 99 in a 2011 NPR readers' poll of best science fiction and fantasy books.
1923_7	In other media Act One of episode 470 of the radio program This American Life is an account of boyhood obsessions with Piers Anthony. The act is written and narrated by writer Logan Hill who, as a 12-year-old, was consumed with reading Anthony's novels. For a decade he felt he must have been Anthony's number one fan, until, when he was 22, he met "Andy" at a wedding and discovered their mutual interest in the writer. Andy is interviewed for the story and explains that, as a teenager, he had used escapist novels in order to cope with his alienating school and home life in Buffalo, New York. In 1987, at age 15, he decided to run away to Florida in order to try to live with Piers Anthony. The story includes Anthony's reflections on these events.
1923_8	Naomi King, the daughter of writer Stephen King, enjoyed reading books by Piers Anthony, which included things like pixies, imps and fairies. After she told her father, "Dad, I just don't like those to be scared. Would you write something with dragons in it?", he wrote The Eyes of the Dragon which was originally published in 1984 and later in 1987 by Viking Press. But What of Earth? Early in Anthony's literary career, there was a dispute surrounding the original publication (1976) of But What of Earth?. Editor Roger Elwood commissioned the novel for his nascent science-fiction line Laser Books. According to Anthony, he completed But What of Earth?, and Elwood accepted and purchased it. Elwood then told Anthony that he wished to make several minor changes, and in order not to waste Anthony's time, he had hired copy editor (and author) Robert Coulson to retype the manuscript with the changes. Anthony described Coulson as a friend and was initially open to his contribution.
1923_9	However, Elwood told Coulson he was to be a full collaborator, free to make revisions to Anthony's text in line with suggestions made by other copy editors. Elwood promised Coulson a 50–50 split with Anthony on all future royalties. According to Anthony, the published novel was very different from his version, with changes to characters and dialog, and with scenes added and removed. Anthony felt the changes worsened the novel. Laser's ultimate publication of But What of Earth? listed Anthony and Coulson together as collaborators. Publication rights were reverted to Anthony under threat of legal action. In 1989, Anthony (re)published his original But What of Earth? in an annotated edition through Tor Books. This edition contains an introduction and conclusion setting out the story of the novel's permutations and roughly 60 pages of notes by Anthony giving examples of changes to plot and characters, and describing some of the comments made by copy editors on his manuscript.
1923_10	Criticism Some critics have described Anthony's portrayal of women characters as stereotypical and misogynist, particularly in the early parts of the Xanth series, and have taken issue with themes of underage sexuality and eroticism within Anthony's work. Jason Heller argues that Anthony's female characters are treated "as obstacles, props, and objects of lust and condescension." Anthony has argued in interviews that these critiques do not accurately reflect his work, and states that he receives more fan mail from female readers than male readers. Personal life Anthony lives on his tree farm in Florida.
1923_11	He and his first wife, Carol Ann Marble Jacob, had two daughters, Penelope "Penny" Carolyn and Cheryl. Penny died in 2009, due to complications from skin cancer, and Cheryl has one child named Logan. Carol Ann died at home 3 October 2019 due to what is suspected to be heart related complications due to a 15 year long battle with chronic inflammatory demyelinating polyneuropathy (CIDP). On 22 April 2020, he married MaryLee Boyance. Religious beliefs Regarding his religious beliefs, Anthony wrote in the October 2004 entry of his personal website, "I'm agnostic, which means I regard the case as unproven, but I'm much closer to the atheist position than to the theist one." In 2017 he stated, "I am more certain about God and the Afterlife: they don't exist." Bibliography References External links Piers Anthony's page at Macmillan.com Extensive 2005 Interview
1923_12	20th-century American novelists 20th-century American male writers 21st-century American novelists American fantasy writers American male novelists American science fiction writers Novelists from Florida Admiral Farragut Academy alumni British emigrants to the United States American agnostics 1934 births Living people Goddard College alumni Science fiction fans United States Army soldiers People from Oxford English agnostics English fantasy writers English science fiction writers American male short story writers Westtown School alumni 20th-century American short story writers 21st-century American short story writers 21st-century American male writers Naturalized citizens of the United States
1924_0	The 2013–14 South Pacific cyclone season was a slightly below average tropical cyclone season, with six tropical cyclones occurring within the basin between 160°E and 120°W. The season ran from November 1, 2013, to April 30, 2014, however, the first four tropical disturbances occurred during October 2013 and were included as a part of the season. During the season, tropical cyclones were officially monitored by the Fiji Meteorological Service (FMS), Australian Bureau of Meteorology (BoM) and New Zealand's MetService. The United States Joint Typhoon Warning Center (JTWC) and other national meteorological services including Météo-France and NOAA also monitored the basin during the season. During the season there were 21 significant tropical disturbances were assigned a number and an "F" suffix by the FMS's Regional Specialized Meteorological Center in Nadi, Fiji (RSMC Nadi), including the remnants of Tropical Cyclone Hadi from the Australian region. The BoM, MetService and RSMC Nadi all
1924_1	estimated sustained wind speeds over a period of 10-minutes and used the Australian tropical cyclone intensity scale, while the JTWC estimated sustained winds over a 1-minute period, which are subsequently compared to the Saffir–Simpson hurricane wind scale (SSHS).
1924_2	Seasonal forecasts
1924_3	Ahead of the cyclone season, the BoM, the FMS, MetService, the New Zealand National Institute of Water and Atmospheric Research (NIWA) and various other Pacific Meteorological services, all contributed towards the Island Climate Update tropical cyclone outlook that was released during October 2013. The outlook took into account the ENSO neutral conditions that had been observed across the Pacific and analogue seasons that had ENSO neutral conditions occurring during the season. The outlook called for a near average number of tropical cyclones for the 2013–14 season, with eight to twelve named tropical cyclones, to occur between 135°E and 120°W compared to an average of 10. At least four of the tropical cyclones were expected to become category 3 severe tropical cyclones, while three could become category 4 severe tropical cyclones, they also noted that a Category 5 severe tropical cyclone was unlikely to occur. In addition to contributing towards the Island Climate Update outlook, the
1924_4	FMS and the BoM both issued their own seasonal forecasts for the South Pacific region.
1924_5	The BoM issued 3 seasonal forecasts for the South Pacific region between 142.5°E and 120°W, one for the Western Southern Pacific region between 142.5°E and 165°E and one for the Eastern Southern Pacific region between 165°E and 120°W. They noted that the tropical Pacific Ocean was currently experiencing neutral ENSO conditions which meant that there was no strong shift expected in the average location of tropical cyclone formation. They also noted that there was nothing in the broad climate drivers to suggest anything, but a typical tropical cyclone season for the South Pacific region. As a result, they predicted that the South Pacific region as a whole, would experience near average tropical cyclone activity during the coming season with a 48% chance of it being above average. The Western region was predicted to have 56% chance of being above average while the Eastern region had a 47% chance of being above average. Within their outlook the FMS predicted that between four and eight
1924_6	tropical cyclones, would occur within the basin compared to an average of around 7.4 cyclones. At least two of the tropical cyclones were expected to become category 3 severe tropical cyclones, while 1-2 might intensify into a category 4 or 5 severe tropical cyclones. They also reported that the tropical cyclone genesis trough was expected to be located near to and to the west of the International Date Line. This was based on the expected and predicted ENSO conditions, and the existence of the Pacific warm pool of sub-surface temperature anomalies in this region.
1924_7	The FMS and Island Climate Update tropical cyclone outlooks both assessed, the risk of a tropical cyclone affecting a certain island or territory. As the tropical cyclone genesis trough of low pressure was expected to be located near to and to the west of the International Date Line, normal or slightly above normal activity was expected for areas near the dateline. It was also predicted that activity between Vanuatu and New Caledonia, as well as east of the International Date Line to be normal or below normal during the season. The Island Climate Update Outlook predicted that Vanuatu and New Caledonia had a reduced chance of being affected by multiple tropical cyclones. The Cook Islands, Fiji, Papua New Guinea, Tuvalu, Tokelau, Samoan Islands, Solomon Islands, Tonga, Wallis and Futuna and French Polynesia's Austral and Society Islands were all predicted to have a normal chance of being affected by a tropical cyclone. Niue and New Zealand were predicted to face an elevated risk while
1924_8	French Polynesia's Tuamotu Archipelago and Marquesas Islands, Kiribati and the Pitcairn Islands, had an unlikely chance of being affected by a tropical cyclone. The FMS outlook predicted that the Cook and Samoan Islands, Tokelau and Niue had a below average risk of being affected by a tropical cyclone. The Solomon Islands, Wallis and Futuna, Vanuatu and Tonga were predicted to face an average risk of being affected by a tropical cyclone. New Caledonia, Tuvalu and Fiji were predicted to face an above average chance of being affected by a tropical cyclone. The FMS also predicted that there was an increased risk of severe tropical cyclones, affecting the region this year when compared to the previous season. There was a very high risk of Wallis and Futuna, Tonga, Fiji and New Caledonia being affected by a severe tropical cyclone. The Samoan Islands, Tokelau, Niue, Solomon Islands and Vanuatu had a high risk, while the Cook Islands had a low to moderate risk of being affected by a severe
1924_9	tropical cyclone.
1924_10	Seasonal summary
1924_11	Ahead of the season formally starting on November 1, 2013, three tropical depressions and a tropical disturbance developed, within the Coral Sea during October. Tropical Disturbance 01F developed on October 19, to the southeast of the Solomon Islands and moved westwards, as a small compact system before it was last noted during the next day. Tropical Depression 02F was first noted on October 19, to the northeast of Suva, Fiji, over the next couple of days the system rapidly consolidated further. However, despite having a good chance of developing into a tropical cyclone, atmospheric convection surrounding the system failed to consolidate enough. The system was subsequently last noted on October 26, as it moved through the island nation of Vanuatu. Tropical Depression 03F was briefly noted on October 22, to the northeast of Honiara on the Solomon Island of Guadalcanal. Tropical Depression 04F developed on October 25, to the southeast of Honiara and affected the islands before RSMC Nadi
1924_12	issued its final advisory on the system during October 27, as it was not expected to develop into a tropical cyclone.
1924_13	Systems Tropical Depression 02F
1924_14	Early on October 19, RSMC Nadi reported that Tropical Disturbance 02F had developed, about to the northeast of Suva, Fiji. Over the next day the system moved westwards within an area of low vertical wind shear and rapidly consolidated further and became a tropical depression during October 20. After the system had started to move towards the south-southwest and continued to consolidate, the Joint Typhoon Warning Center issued a Tropical Cyclone Formation Alert for the system during October 21. However, this alert was cancelled during the next day after satellite imagery revealed a poorly defined low level circulation center, with unorganized atmospheric convection that had not consolidated and vertical wind shear over the system had started to increase. RSMC Nadi subsequently issued their final warning on the system during October 23, as the system weakened into an area of low pressure over the islands of Vanuatu. However, the remnant area of low pressure was monitored until October
1924_15	26, as it moved through Vanuatu.
1924_16	Between October 23–24, heavy rainfall associated with the system, caused flooding and landslides on the island of Paama in Malampa Province. Because of the islands geography, impacts were reported to most villages on the island with specific damage reported to homes, roads, a school and the islands air strip. Other impacts included over 160 food gardens being destroyed and the ground water supply was contaminated. Severe Tropical Cyclone Ian During January 2, RSMC Nadi reported that Tropical Disturbance 07F had developed to the southeast of Futuna Island. Over the next three days the system gradually developed further underneath an upper-level ridge of high pressure, within an area of moderate vertical wind shear, as it slowly moved towards the southwest. Late on January 5, the JTWC designated the system as Tropical Cyclone 07P, before RSMC Nadi named the system Ian, after it had become a category 1 tropical cyclone on the Australian scale. Tropical Cyclone June
1924_17	During January 13, the FMS reported that Tropical Disturbance 08F had developed, along a surface trough of low pressure to the southeast of the Solomon Island Makira. Over the next couple of days the system moved south-westwards and moved into the Australian region during January 15, where it was classified as a monsoonal low. The disturbance, however, exited that basin on January 16 without upgrading it to a tropical cyclone. The RSMC Nadi had reported that the system intensified into a Category 1 tropical cyclone and was named June the next day. June caused at least one fatality in New Caledonia, possibly two. Tropical Cyclone Edna
1924_18	During February 4, Tropical Cyclone Edna moved into the basin, just after deep convection surrounding the system had significantly improved and it had re-intensified into a tropical cyclone. Over the next day the system was steered to the south-southeast by a mid-level ridge of high pressure and affected the French Territory of New Caledonia. Both RSMC Nadi and JTWC subsequently estimated that the system had reached its peak sustained winds of , which made it a category 2 tropical cyclone on the Australian scale. Tropical Cyclone Kofi On February 24, RSMC Nadi reported that Tropical Depression 15F had developed about west of Nadi, Fiji. This was quite close to Tropical Depression 14F, and JTWC appear to have regarded them as the same system. There had also been severe flooding in Central and Eastern parts of Fiji Islands on February 27. During Kofi's duration, the system submerged many homes in the Fiji Islands. Severe Tropical Cyclone Lusi
1924_19	Early on March 7, RSMC Nadi reported that Tropical Disturbance 18F had developed about to the west of Nadi, Fiji. Over the next two days the system moved towards the north-northwest and slowly consolidated, as atmospheric convection wrapped into the systems low level circulation center, before RSMC Nadi reported during March 9, that the system had developed into a tropical depression. Tropical Cyclone Mike
1924_20	On March 12, RSMC Nadi reported that Tropical Disturbance 19F had developed about to the southeast of Pago Pago, American Samoa. Over the next few days the system gradually developed further before early on March 19, RSMC Nadi reported the system had become a category 1 tropical cyclone on the Australian scale and named it Mike. The JTWC subsequently initiated advisories on the system and assigned it the designation Tropical Cyclone 20P. Later that day RSMC Nadi and the JTWC issued their final advisories on Mike, as it moved below 25S and transitioned into an extratropical cyclone. The extra-tropical remnants of the cyclone were subsequently monitored by TCWC Wellington, until they were last noted during March 24, while they were located over to the east of Wellington, New Zealand.

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.