Archived from Will Payne's (N4YWK) site, as it was a BSRG project spun off from the BSRG ATV repeater.

Here is the Hawgplexer diagram. Click to enlarge

Hawgplexer Diagram



Forget everything you knew about radio, you are entering a new paradigm! Two diodes in a funny piece of waveguide, a Gunnplexer, form the front end of a full duplex microwave radio. The common homodyne type Gunnplexer may be used for microwave communications with the addition of a 30 MHz wideband receiver or scanner and some miscellaneous circuitry to provide power, frequency control and modulation.

These miscellaneous functions are all provided by the HAWGPLEXER kit. If you have a gunnplexer and a receiver, this simple kit will convert them into a full duplex microwave radio. The kit is composed totally of Radio Shack parts. The HAWGPLEXER continues the fine tradition of the HAWG FENCE antenna by W4KIP, a $3 ATV antenna with 11 db gain made of hawg fence wire. The HAWG tradition provides almost-commercial-performance radio equipment which can be cobbled together from cheap household items.

The common homodyne Gunnplexer is found in automatic door openers, motion sensors, and speed guns. While not designed for FM communications, a little ingenuity overcomes this deficiency.


The Gunnplexer contains a Gunn diode, which is a negative resistance oscillator. The oscillator runs at a frequency determined by the resonant waveguide cavity in which it is mounted. A mixer diode is mounted outside the cavity, which mixes the outgoing and incoming microwaves. Two Gunnplexers in communication are tuned 30 MHz apart, each mixer detects a 30 MHz product modulated by both its own and the other Gunn oscillator. A 30 MHz receiver amplifies and demodulates the signal.

The homodyne Gunnplexer is normally tuned by mechanical means only, but drifts with temperature, VSWR and voltage. By slightly varying the Gunn supply and adding some amplified audio to it, we achieve some tuning and FM modulation in the homodyne type units.

Variable DC supply voltage to the Gunn diode is regulated by the LM317T and associated components. Main tuning potentiometer controls the voltage from around 4v up to around 11v. Electrolytic capacitors filter and stabilize the regulator. The audio amp module amplifies the mike signal to sufficient level for modulation. Amplified audio is injected into the Gunn supply downstream of a 10 ohm resistor which isolates the audio from the bypass capacitors and regulator.


1. Build the audio module kit as directed, EXCEPT put C4 in backwards.

2. Use discarded leads to add "pins" to the module board.

3. Arrange the audio module and LM317T conveniently on the perfboard, pay attention to keeping ground leads short.

4. Wire the perf board components per the schematic. Leave flying leads for power, inputs, outputs, and controls.

5. Install perfboard, connectors and controls in a chassis box and complete the chassis wiring.

6. Cut DIN cord in half, install DIN pigtails on Gunnplexer(s).

7. Without Gunnplexer connected, apply power, check no smoke. Check 12v on the audio module and regulator input. Vary the pot through its range while looking for a smoothly varying voltage at the gunn diode output. PROCEED NO FURTHER UNTIL CHECKS ARE GOOD.

8. Connect Gunnplexer, power up and check for Gunn current and mixer current. To read Gunn diode current in mA, measure the DC voltage drop across the 10 ohm resistor, and multiply by 100. Typical Gunn operating point might be 8 v at 210 mA. (2.1v drop) Apply a milliammeter from the mixer jack to ground to measure mixer current, normally a few mA for a healthy Gunnplexer. PROCEED NO FURTHER UNTIL CHECKS ARE GOOD.

9. Connect receiver, microphone, power up and test against a known good gunnplexer station or test equipment. Tune to center frequency with nominal Gunn voltage, and set deviation.

10. Have fun on 10250.0 MHz !


NEVER look into powered waveguides or loaded gun barrels !!

Use a meter to determine the point where the rated voltage of your Gunnplexer occurs, proceed further AT YOUR OWN RISK. I have never lost a diode operating as much as 1 volt above its rating. But it can happen. It is safer to tune to the strongest signal BELOW the rated Gunn voltage.

73 es enjoy de n4ywk

will.e.payne at