[sunthaiboy]

Thanks for your inputs folks. The 2 gunnplexers I bought were 10mW devices. They were removed from auto sliding door openers which also used PIR detectors to help eliminate false triggers. They were acquired for £30 a pair from a well known E-site recently. I to fabricated rather large horns to help improve the gain (18dBi). Alas even at 0.5 length, these failed to get the horizontal 3dB beam below 50 degrees. Parabolic reflectors and feed horns at this frequency is too unwieldy and tricky to fabricate unless your into to car panel fabrication. I have now decided to go down in wavelength from cm to nm and use pulsed scanning lasers. The gunnplexers are now pressed into use as howling proximity detectors. Used in pairs spaced at 10m (without the horns) they are quite effective when the Schottky diode output is fed into V to F converters and a hand full of Op Amps.....of which my stock has been growing alarmingly for 30 years.
Robert