Gunnplexer FAQ WHAT IS A GUNNPLEXER? Forget everything you knew about radio, you are entering a new paradigm! These two diodes in a funny piece of waveguide are a full duplex microwave radio. Simplex contacts are no more, it only recieves while transmitting, and contacts occur on a frequency PAIR. We use 30 MHz voice duplex offset. Gunnplexer transcievers have one transmit and TWO recieve frequencies, 30 MHz on either side of the transmitter. There is enough bandwidth for voice, WBFM stereo, video, and 10,000,000 bps data. Gunnplexers occur in two types, the common homodyne, or motion detectors, and the varactor tuned type, used for communication. Homodyne Gunnplexer Varactor Gunnplexer Gunn + mixer diode Gunn + varactor + mixer diode People detectors, speedguns Communications Mechanically tuned only Mech. + electronic tuning Freq push: pot luck, maybe 10 MHz Varactor tuning > 100 MHz In a homodyne unit, we take advantage of the Gunn oscillators' instability by varying the DC supply to "push" the frequency slightly. This is usually enough to produce FM modulation and give some fine tuning range to correct for temperature drift. Thus the common 'people detector' also communicates. We STRONGLY RECOMMEND you mechanically tune your unit to a common frequency using test equipment, then Loctite the tuning screw. Use frequency pushing for fine tuning. If you move the tuning screw to talk to a buddy, soon everyone diverges from the channel and it becomes difficult to find and communicate with each other. WHAT ELSE DO I NEED? You need DC power, an audio source to transmit, and a wideband FM receiver to act as the IF strip. The Gunn DC voltage should be marked on the Gunnplexer, usually +8.0 v. Transmit audio is amplified and superimposed on the Gunn DC supply. The reciever is connected to the Gunnplexer mixer. Quick and dirty transmit can be simply a 9v battery and the speaker output of an HT in parallel. A better solution is a variable DC regulator combined with an audio amplifier, which gives fine tuning and a mike input. The function of reciever IF and discriminator may be provided by a scanner, or a dedicated receive circuit board, connected to the Gunnplexer mixer. 20 GUNNPLEXER TIPS AND FACTS NEVER peer into powered waveguides or loaded gun barrels !! Microwave heating can especially damage the eyes and testes. WWII secret X-radar used brass bed frame tubing as waveguide. The X-band is 8.0-12.4 GHz, the ham portion is 10.0 to 10.5 GHz. 10 GHz wavelength is 3cm, or about 1-3/16 inches. Robert Gunn invented this negative resistance oscillator diode. Gunnplexer tuning screw travels IN to LOWER the frequency. Frequency drifts due to: DC voltage, temperature, VSWR. Tune your gunnplexer with its antenna, to prevent VSWR pushing. X-band Gunns temperature drift typically 1 MHz per 3 degrees. Warm up Gunnplexers at least 10 min before tuning or operating. Use cover-cover or choke-cover flange joints, never choke-choke. Suitable X-band waveguide is WR-90, 1.0x0.5 in OD, 0.9x0.4 in ID. The open end of a waveguide has VSWR of 1.6, gain of 7 dbi. A small horn may have 15 db gain, a portable dish, over 30 db. People detectors run typically .005 W, speedguns up to .25 W. Propagation is Line-Of-Sight (LOS), range >100 miles possible. Slit the end of a waveguide, flare to 1.0x0.75 to feed a dish. Be sure your Gunn diode doesn't oscillate at audio or HF as well. Don't swim for 15 minutes after eating. HAWGPLEXER KITS ! There is a Hawgplexer kit designed to get your homodyne gunnplexer on the air with proper modulation and fine tuning. Cost is $25, and 12 kits are available. You provide the case, microphone, and 30 MHz wideband FM receiver or scanner. The Hawgplexer kit is a quickie design with all Radio Shack parts to get folks on 10250 MHz in time for field day. Unfortunately, I have learned the audio amp module is being discontinued by Radio Shack. If enough interest is present, I will design and build a circuit board to do the job. Also a companion 30 MHz receiver board is in the works, so sign up now! The Hawgplexer kit will work with either the companion 30 MHz receiver board or your wideband FM scanner on 30 MHz. HAVE FUN ON THE X-BAND ! Hope to hear you on field day! Some of us plan to go to Pigeon Mountain and set up a big dish varactor tuned station on X-band. Portable stations can disperse to other mountains to see if they can contact the home station and each other. Pick a mountaintop and join us for field day! 73 de N4YWK will.e.payne@lmco.com