Note
Ham Radio, Mar 1977, p. 86.
QST, Oct 1977, p. 108.
QST, Apr 1978, p. 167.
Also see QST, Aug 1978, p. 99.
QST, Apr 1981, p. 142.
The Microwave Associates solid-state Gunnplexer transceiver is designed especially for the amateur 10 GHz band, and consists of a varactor-tuned, frequency-modulated Gunn diode oscillator and Schottky mixer diode. The rear portion of the unit consists of a Gunn diode oscillator which directly converts DC ( +I0 VDC nominal) to 20 mW of RF energy. The oscillator is preset to 10.250 GHz, the center of the amateur band.
Mechanical tuning allows the center frequency to be tuned ±I00 MHz; the built-in varactor is used for frequency modulating the device and will deviate the center frequency up to 60 MHz, depending upon the applied tuning voltage.
The receiver section of the Gunnplexer consists of a low-noise Schottky mixer diode which has a noise figure of about 12 dB when used with a low-noise IF strip. A small amount of power from the Gunn oscillator (about 0.5 mW) is applied to the mixer diode through a ferrite circulator integrated into the waveguide mount. The circulator also isolates the receiver and transmitter functions of the module. A horn antenna with 17 dB gain is available as an accessory.
Since the Gunn oscillator provides both transmit power and mixer injection, the setup for radio communications is similar to that used with klystron-based polaplexers (see page 40, this issue), i.e., the center frequencies of the Gunnplexers used at each end of a communications link must be offset by the IF frequency, typically 30 MHz. FM broadcast receivers can also be used for the IF system, with AFC applied to the Gunnplexer tuning varactor to minimize frequency drift (which is -350/ºC maximum without AFC).
Maximum range with the 20 mW Gunnplexer depends on a number of factors including required FM signal-to-noise ratio, FM deviation, IF bandwidth, and antenna gain. However, assuming a 10-dB signal-to-noise ratio (the threshold of speech in an FM system), a line-of-sight path between stations, and the accessory 17-dB horn antennas, maximum range is about 25 miles with a 240 kHz IF bandwidth (that used in FM broadcast receivers). If the IF bandwidth is decreased to 50 kHz, maximum range is about 55 miles.
The Gunnplexers can be used for two-way communications, as a link between repeater sites, security alarms, or FM doppler radar systems. A separate power supply, FM modulator, and receiver must be provided by the user.
References
Solid state microwave RF generators. Ham Radio, Apr 1977, p. 10.
Key words: Gunplexer