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RDF systems using mechanically swung loop or dipole antennas were common by the turn of the 20th century. Prominent examples were patented by John Stone Stone in 1902 (U.S. Patent 716,134) and Lee de Forest in 1904 (U.S. Patent 771,819), among many other examples.
The AN/FLR-9 Operation and Service Manual [2] describes the array as follows: . The antenna array is composed of three concentric rings of antenna elements. Each ring of elements receives RF signals for an assigned portion of the 1.5 to 30-MHz radio spectrum.
When the loop is aligned at right angles to the signal, the signal in the two halves of the loop cancels out, producing a sudden drop in output known as a "null". Early DF systems used a loop antenna that could be mechanically rotated. The operator would tune in a known radio station and then rotate the antenna until the signal disappeared.
Ferrite antennas are usually enclosed inside the radio receiver. Ferrite loop antennas are made by winding fine wire around a ferrite rod. They are almost universally used in AM broadcast receivers. [12] (p 23) [d] Other names for this type of antenna are loopstick, ferrite rod antenna or aerial, ferroceptor, or ferrod antenna.
One drawback to any DF system using loop antennae is that the antenna is equally sensitive on both the front and the back, so there is always a 180 degree ambiguity in the measurements - the transmitter might be on either side of the antenna. To address this, many DF systems added an additional antenna, the sense antenna (unrelated to the sense ...
"Small" loop antennas are loops of wire or metal tubing designed for use as antennas at frequencies where their perimeter is smaller than a half-wave; they are not naturally resonant on any frequency they are used on, and must be resonated artificially, usually by attaching a capacitor across their feedpoint. Composite antennas
A transmatch (antenna tuner) is not required to use this antenna near its nominal design frequency of 14 MHz, and judicious length adjustments can sometimes include one other frequency band. All other frequencies require a transmatch. [citation needed] There are many variants of the G5RV antenna. Two variations of the G5RV design, called ZS6BKW ...
A common RDF antenna design is the loop antenna, which is simply a loop of wire with a small gap in the circle, typically arranged to rotate around the vertical axis with the gap at the bottom. [3] Some systems used dipole antennas instead of loops. Before the 1930s, radio signals were generally in the long wave spectrum. For effective ...