The 7235 consists of two identical receiving loop antennas arranged in a “crossed loop” configuration. Because loop antennas that operate at low frequencies tend to be very large, the 7235 uses an active magnetic loop design to minimise the physical size of the antenna. The 7235 contains two multi-turn loop antennas that are wound around high permeability ferrite rods to increase the effective area of the loop, and thereby increase the antenna sensitivity at low frequencies. The signal output of each loop is buffered by a high-dynamic-range active amplifier to improve the antenna noise figure.
In addition to the two active loops, the 7235 system includes a low-profile active monopole antenna (Model 7031). The signal from this third antenna is used as a reference in the DF algorithm to eliminate the 180 degree angle of arrival ambiguity that is inherent in crossed loop DF antennas.
The 7235 is a compact, active antenna system used for direction finding of signals in the MF and HF bands. It is packaged in a small, but rugged, plastic housing that is suitable for fixed or mobile installations.
The 7235 is optimised over the range of 500 kHz to 20 MHz and operates over the frequency range of 300 kHz to 30 MHz. It is designed for DF systems using the Watson-Watt DF method. In this system, the azimuth angle of arrival of a vertically polarized signal is determined by measuring and comparing the phases and amplitudes of the received signal at the outputs of two loop antennas which are oriented at 90 degrees to each other.
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