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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.
If a small loop antenna's loss is 50 dB (as if the antenna included a 50 dB attenuator), then the electrical inefficiency of that antenna will have little influence on the receiving system's signal-to-noise ratio. In contrast, at quieter frequencies at about 20 MHz and above, an antenna with a 50 dB loss could degrade the received signal-to ...
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 nulls in the radiation pattern of small receiving loops and ferrite core antennas are bi-directional, and are much sharper than the directions of maximum power of either loop or of linear antennas, and even most beam antennas; the null directionality of small loops is comparable to the maximal directionality of large dish antennas (aperture ...
The rhombic antenna was designed in 1931 by Edmond Bruce [1] and Harald Friis, [2] [3] It was mostly commonly used in the high frequency (HF) or shortwave band as a broadband directional antenna. As of 2023, one last remnant pole still stands from the AT&T pole farm which was located in Mercer County, New Jersey
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 ...
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 ...
A quad antenna is a type of directional wire radio antenna used on the HF and VHF bands. A quad is a Yagi–Uda antenna ("Yagi") made from loop elements instead of dipoles: It consists of a driven element and one or more parasitic elements ; however in a quad, each of the loop elements may be square, round, or some other shape.