2m ARDF RX, ROX-2T

ROX-2T

This receiver is based on an original design by OK2BWN in which the IF amplifier, detector and audio amplifier is provided in a single TDA1083 IC.

The TDA1083 is a one chip AM/FM radio widely used in consumer radios until the early 2000’s. The TDA1083 and many pi-compatible variants have been around for a very long time so ICs should not be too difficult to obtain or salvage. The equivalent TA7613AP is used in this project.

The ROX-2T uses a novel way of controlling the gain of the SA602 mixer (as found in the Elecraft K1 transceiver) but the SA612 must be directly feed by the stabilized supply voltage to the chip or a through a RFC, to minimize pulling of the VFO.

ROX-2T

The resulting ARDF RX is just about as simple as a superhet can get with get two RF devices, and no surface mount components, (apart from the varicap diode.)

The ROX-2T is not suitable for (FM) foxhunting. If the fox stops talking, there will be no modulation to detect! so it is solely aimed at Radio Orienteering using MCW/AM transmissions.

CONSTRUCTION NOTES

L1, input coil - 1:6 on a T37-12 or T37-17 toroid.
The primary single turn winding is a full turn secured with the ends twisted. The secondary winding (3T+3T) is wound handed for each side of the primary winding.

note: The front mounting holes are ’live’, also being the antenna input terminal, so may need to be insulated from the enclosure.

INTEGRATED ANTENNA

This receiver is typically paired with the 3 element is based on the WB2HOL yagi described elsewhere on this web site.

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CONSTRUCTION NOTES

INTEGRATED ANTENNA