Radar Detector Gunn -gun

Fig. 1. Waveguide circulator 10-GHz transceiver. 73 Amateur Radio • January, 1987

It's not very hard to set up a station for 10

GHz. I have been experimenting with a portion o\"a Solfan Doppler-radar intrusion alarm that I converted for use at 10.250 GHz. These alarms can be found pretty easily at hamfests, and I have heard many people speak of the high availability of these units in Europe, where this type of alarm circuit is used extensively.

I have found two different types. Whatever unit you obtain can be used with the methods described here. The first unit that I'll describe is the Solfan Intrusion Alarm Gunn diode mount and detector assembly. This has both a Gunn diode and detector diode mounted in the same cast waveguide mount. The waveguide size is WG-16, or 0.4" high by 0.9" wide. It does not have varactor tuning for ate like the Microwave Associates Gunnplexer. The mount is about three inches long with the Gunn diode placed at the rear center of the cavity and coupled to the mixer diode by a small round waveguide iris midway between the two ends of the cavity.

The detector diode is mounted offset to one side of the forward waveguide cavity for low coupling. Both cavities have tuning screws for impedance matching and frequency adjustment. Photos A and B showr the end and side views of the various Solfan units. Photo A shows the internal waveguide construction and where the diodes are mounted. Note that the Gunn diode is mounted dead center in the cavity, while the larger detector diode is mounted on the side of the cavity walL

The second type of Solfan mount is a single Gunn diode transmitter-type unit, This

Photo A. Waveguide flange end showing from left to right: ins coupling from single Gunn mounts, detector diode on the side of the unity, very small Gunn diode mounted in the cavity center, and another single Gunn mount with a srrutll horn.

Photo B, Side view of the Solfan Gunn mounts. The ends ore the single oscillator units. The center two units are the double mount (oscillator-detector assemblies). Various adjustments ami connection terminals are visible.

device docs not have a detector diode ai-tached with its cavity. I don't know what the detector mount looks like, as I haven't run into one yet. I've used this mount as a single point source to test other transceivers and have mounted one unit into one port of a 3-port circulator, with a detector mount and an antenna tied to the third port. While sensitivity was slightly lower

"Operation during contest weekend may give some stations an edge of quite a few points by working a surprising number of different grid squares and contact points."

than on other models, it did perform quite well. See Fig. 1 for details on the circulator system.

There arc many different con 1'igurations of detectors, waveguides, and oscillators thai will produce a working station. What your finished prinjuct looks like depends on the materials you arc able t<i scrounge up from junk boxes and swap meets. Photo C of N6IZW\s completed transceiver using a circulator and detector mount coupled w ith PC boards described in this article sho\*s how simple components can be assembled into a

Photo C. 10-GHz transceiver (N61ZW) mounted on a large horn antenna♦ The system uses a single Solfan Gunn oscillator, circulator, dunk detector, and the completed i-f amp, S-meter modulator circuit board.

complete system package. Photo D depicts a minimum transceiver.

System Description

To be able to construct a full-duplex transceiver for 10 GHz. you need four basic components: a 30-MHz i-f amp, a power-

supply modulator, an i-f preamp. and a Gunn diode waveguide cavity/detector diode as* sembly. II you can find one of these units at your local swrap meet, it will make this project ver> easy to build. If you cannot obtain one of the units, a suitable oscillator mourn and detector assembly may he constructed

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Fig. 2, Signal-strength meter circuit (a) schematic, (h i circuit boardr foil sidef and fc) parts placement.

73 Amateur Radio * January! 1987 41


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