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Old 20th Nov 2018, 10:32 am   #1
sunthaiboy
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Default Gunnplexers and messing about at 3cm

I have always had a passion for Radar and wanted to make a home-brew one. Has anyone on the forum done something similar? I'm experimenting using 2 Gunnplexers/receivers, V/F converters and some FFT processing to make a simple tracking searchlight (or laser pointer). The cost of the older small boat or ex MoD a/c radars seem rather appealing but quite complex to interface (and the power demands are quite high). I also want to detect not cook my moving meat....

Last edited by Paul Stenning; 20th Nov 2018 at 10:40 am. Reason: Corrected spelling of Gunnplexers
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Old 20th Nov 2018, 7:51 pm   #2
merlinmaxwell
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Default Re: Gunnplexers and messing about at 3cm

There was a bistatic radar article in Wireless World in the 80's (I think) using the UHF radar at Heathrow and a standard TV antenna.
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Old 24th Nov 2018, 7:54 am   #3
Diabolical Artificer
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Default Re: Gunnplexers and messing about at 3cm

Arn't there little modules you can buy that are "pantry" radar units? Sure I've seen a couple of video's about this on Utube. There's no display but from memory they had a range of about 10m.

Andy.
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Old 24th Nov 2018, 10:22 am   #4
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Default Re: Gunnplexers and messing about at 3cm

Yes, search HB100 radar in the usual places, velly, velly cheap.
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Old 24th Nov 2018, 8:41 pm   #5
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Default Re: Gunnplexers and messing about at 3cm

MIT has a low powered design (10mW) that is good for taking speed measurements etc. It uses a tin-can style aerial. I’ll try to find the resource online again...
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Old 25th Nov 2018, 10:15 am   #6
sunthaiboy
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Default Re: Gunnplexers and messing about at 3cm

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
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Old 25th Nov 2018, 5:47 pm   #7
astral highway
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Default Re: Gunnplexers and messing about at 3cm

Here's the MIT link...

https://ocw.mit.edu/resources/res-ll...uary-iap-2011/

It's entitled:

'Build a Small Radar System Capable of Sensing Range, Doppler, and Synthetic Aperture Radar Imaging' and is truly excellent. There is also a course of about ten lectures. It has some maths involved but that's because it's part of a prestige university course and it couldn't just be about assembly! The course was sponsored by the US Department of The Air Force.

It's not necessary to do the maths to complete and operate the radar. You'll get great results at these low milliwatt levels, really minimal danger. There's software called MATLAB if you do want to.
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Old 27th Nov 2018, 11:28 am   #8
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Default Re: Gunnplexers and messing about at 3cm

I understand these were heavily used in the Pirate radio scene in the 90's. They were used to link studios by line of sight to the transmitter location, so when it was inevitably traced the studio wouldn't be raided and all the gear taken!

I believe at one time such devices were used as sensors at pedestrian crossings, causing them to be pilfered and damaged by nefarious chaps to use as studio links

You may find information on using them in a similar, but LEGAL regard if you look around online
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Old 27th Nov 2018, 8:16 pm   #9
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Default Re: Gunnplexers and messing about at 3cm

The RCWL-0516 radar doppler boards are available for about 50p each (5 off) from well-known auction/ecommerce sites. A bought five of these recently and just playing around with them on the workbench they seem very sensitive indeed. Not tried any modification / hacking yet but fascinating devices for very little cash.
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