G3XTZ DF Rx Details

Posted on Feb 4, 2014

The receiver is built on a single-sided printed circuit board which measures 2 by 4. 3 inches. The small size means that the board can be fitted into a wide variety of enclosures, which should be well screened. The main directional signal is picked up by a tuned ferrite rod (or loop) aerial and fed, via the R. F. attenuator (RV1) to a low-noise FET

G3XTZ DF Rx Details
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R. F. amplifier (TR2). A second FET R. F. stage (TR1) amplifies the signal from a vertical whip aerial and can be switched into circuit to give a heart-shape response so that the direction of received signal can be determined. This direction is not accurate, but serves to eliminate one of the two sharp null directions that the ferrite aerial provides. The amplified signal is tuned in a Hi-Q coil (L1) and fed into the TCA440 receiver integrated circuit. This I/C includes R. F. amplifier, balanced mixer, separate local oscillator, I. F. amplifier and voltage stabilizer. The local oscillator is tuned by L2 with VC3 and covers 2. 265 to 2. 455 MHz which converts the incoming signals of 1. 81 to 2. 00 MHz to a 455 kHz I. F. This signal is fed from the mixer through the 5. 5 kHz bandwidth Mechanical filter (CF1) and back into the TCA440 I. F. amp. The amplified signal is rectified by diode D2 and appears as audio across the volume control (RV4). Automatic gain control is not normally used in a direction finding receiver (this would mask the effect of rotating the aerial) so the gain of the R. F. and I. F. amplifiers are set by a fixed, stabilized voltage ( about 0. 7 Volt maximum ) from trimmer resistor RV2. Adjustable audio levels are fed from the volume control to a single, high gain audio amplifier which drives the headphones to adequate level. Medium to high impedance headphones are preferred. TR4 with L3 form a simple Beat...

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