Warning ! This receiver has no AGC, so has the potential to cause ear damage if not correctly used. If required, increase the the value of R15 to limit the audio output volume.
This receiver uses an IC variant of the TDA1083 which is used in a well known ARDF design by OK2BWN.
The TDA1083 or TA7613AP is a one chip AM/FM radio, complete with audio amplifier. It has been around for a very long time so ICs should not be too difficult to obtain or salvage.
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.
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 squarely aimed at Radio-O using MCW/AM transmissions.
The main winding L1 (3T+3T) must be wound in the same sense for each half i.e. NOT mirrored
Use a piece of 26swg wire 100mm long, folded in half. Tin the ends and centre fold. The easiest way to remove the enamel is to boil it off by holding the wire ends in a solder blob.
The 3 element is based on the WB2HOL yagi described elsewhere on this web site. On the version for the ROX2 there is no hairpin loop because there is no requirement to match to a 50ohm feeder. The antenna is directly connected to the front-end of the receiver. The driven element is longer than shown in the WB2HOL yagi.
The driven element connection to the ROX2 is the shown below.