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A common application of loading coils is to improve the voice-frequency amplitude response characteristics of the twisted balanced pairs in a telephone cable. Because twisted pair is a balanced format, half the loading coil must be inserted in each leg of the pair to maintain the balance.
The coil is added at the base of the whip (called a base-loaded whip) or occasionally in the middle (center-loaded whip). In the most widely used form, the rubber ducky antenna, the loading coil is integrated with the antenna itself by making the whip out of a narrow helix of springy wire. The helix distributes the inductance along the antenna ...
A loop antenna is a radio antenna consisting of a loop or coil of wire, tubing, or other electrical conductor, that for transmitting is usually fed by a balanced power source or for receiving feeds a balanced load. Within this physical description there are two (possibly three) distinct types:
With a vertical antenna a loading coil at the base of the antenna may be employed to cancel the reactive component of impedance; small loop antennas are tuned with parallel capacitors for this purpose. An antenna lead-in is the transmission line, or feed line, which connects the antenna to a transmitter or receiver.
Earth antennas are made of wires actually buried under the soil, hence also called buried antennas; if laid onto the soil instead of buried in it, they are called ground antennas. Most amateur use is limited to non-directional MF and LF receiving antennas, but transmitting ground dipoles [ad] are used for military communication with submarines.
The capacitance is usually canceled out by an added loading coil or its equivalent; the loading coil is conventionally placed at the base of the antenna for accessibility, connected between the antenna and its feedline. One of the first uses of 'T' aerials in the early 20th century was on ships, since they could be strung between masts.
Not being close to 3 / 2 wave, this antenna's impedance has a large (negative) reactance and can only be used with an inductive impedance matching network (a tapped loading coil or a so-called antenna tuner). It is a desirable length because such an antenna has the highest gain for any dipole which isn't a great deal longer.
Loading coil - an inductor used to add inductance to an antenna, to make it resonant, or to a cable to prevent distortion of signals. Variometer - an adjustable inductor consisting of two coils in series, an outer stationary coil and a second one inside it which can be rotated so their magnetic axes are in the same direction or opposed.