Model 7235

The Model 7235 DF Antenna is a compact, active antenna system used for direction finding of signals in the MF and HF bands. It consists of two identical receiving loop antennas arranged in a “crossed loop” configuration. To overcome the size limitations of low-frequency loop antennas, the 7235 employs an active magnetic loop design. This design effectively minimizes the physical size of the antenna.

For enhanced sensitivity at low frequencies, the Model 7235 DF Antenna incorporates two multi-turn loop antennas wound around high permeability ferrite rods. These rods increase the effective area of the loop, thereby boosting antenna sensitivity. To further improve the antenna noise figure, the signal output of each loop is buffered by a high-dynamic-range active amplifier.

The Model 7235 system also includes a low-profile active monopole antenna (Model 7031) in addition to the two active loops. This third antenna serves as a reference in the DF algorithm, eliminating the inherent 180 degree angle of arrival ambiguity found in crossed loop DF antennas.

Packaged in a small yet rugged plastic housing, the 7235 is suitable for both fixed and mobile installations. It offers optimization across the frequency range of 500 kHz to 20 MHz and operates from 300 kHz to 30 MHz. Specifically designed for DF systems employing the Watson-Watt DF method, it determines the azimuth angle of arrival for vertically polarized signals by measuring and comparing the phases and amplitudes of the received signal at the outputs of the two loop antennas, which are oriented at 90 degrees to each other.

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