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A loading coil or load coil is an inductor that is inserted into an electronic circuit to increase its inductance. The term originated in the 19th century for inductors used to prevent signal distortion in long-distance telegraph transmission cables.
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:
Loop antennas consist of a loop (or coil) of wire. Loop antennas interact directly with the magnetic field of the radio wave, rather than its electric field as linear antennas do; for that reason they are on rare occasions categorized as magnetic antennas, but that generic name is confusingly similar to the term magnetic loop normally used to ...
The high reactance vs the low resistance give the antenna a high Q factor; the antenna and coil act as a high Q tuned circuit, reducing the usable bandwidth of the antenna. At lower frequencies mast radiators are replaced by more elaborate capacitively toploaded antennas such as the T antenna or umbrella antenna which can have higher efficiency.
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.
Moxon antenna for the 20-meter band.The antenna is the faint rectangle of wires held in tension by the bent X-shaped support frame. Moxon antenna for the 2-meter band. The Moxon antenna or Moxon rectangle is a simple and mechanically rugged two-element parasitic array, single-frequency antenna. [1]
These electrically short antennas need loading coils at the base of the antenna to bring them into resonance. Many antenna types, such as the umbrella antenna and L- and T-antenna, use capacitive top-loading (a "top hat"), in the form of a network of horizontal wires attached to the top of the vertical radiator.