WW Microwave Intruder alarm? - UK Vintage Radio Repair and Restoration Discussion Forum

boiss · 18th Aug 2023, 11:07 pm

Not really radio but it was an interesting project. Back in the 80s I built the circuit board for the Microwave Intruder Alarm published by Wireless World and bought a few mw modules (Gunn diode and Det diode) Finally after 40 years I decided to hook it all up. I had built a horn with a designed 20dB of gain. I built it into a case with a plastic front. the plastic is mega reflective and I get upwards of -300mV (Even -1V) on the Det. Removing the front panel brings the voltage down to -25mV, a workable figure. However the led is dimly lit always. I have no scope so I am wondering if this is down to the electrosmog indoors?
Did anyone else build this project dating back to March 1980?
Cheers
Mike

Graham G3ZVT · 21st Aug 2023, 11:38 pm

The first itteration of security lights outside my daughters high school used microwave sensors, which quickly disinterested with rust and we're duly replaced with PARs.

boiss · 22nd Aug 2023, 12:50 am

Mine has an Ally and plastic casing and the microwave bit is chrome plated brass with a copper horn, all in the casing. It rarely rains here and the unit woud be in a protected area.
The intruder alarm followed on from a mw audio link project, from WW 1977.

DrStrangelove · 22nd Aug 2023, 11:11 am

I played with the Maplin version of it which was without the tinplate horn shown in the WW article.

It didn't seem overly sensitive, presumably due to the lack of the horn.

It's still around here "somewhere".

boiss · 24th Aug 2023, 12:06 am

Had another play with it yesterday, I made my own horn cutting a piece of wg16 up. Should have a gain of about 20dB. From what I gathered the module on its own was quite sensitive, mine wasn't sold with the 5dB antenna.The voltage on the mixer diode in the clear is about -15mV and varies according to what is happening in front of it. The voltages on the first two 741s (747) look about right. The voltages on the 3rd 741 are way off. I appear to have loads of AC etc. Need to dis the gunn, short the mixer and see what I'v got going on. Got loads of 741s. BTW I think I got the pcb from Maplin in Soton.

18th Aug 2023, 11:07 pm	#1
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	WW Microwave Intruder alarm? Not really radio but it was an interesting project. Back in the 80s I built the circuit board for the Microwave Intruder Alarm published by Wireless World and bought a few mw modules (Gunn diode and Det diode) Finally after 40 years I decided to hook it all up. I had built a horn with a designed 20dB of gain. I built it into a case with a plastic front. the plastic is mega reflective and I get upwards of -300mV (Even -1V) on the Det. Removing the front panel brings the voltage down to -25mV, a workable figure. However the led is dimly lit always. I have no scope so I am wondering if this is down to the electrosmog indoors? Did anyone else build this project dating back to March 1980? Cheers Mike

21st Aug 2023, 11:38 pm	#2
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,581	Re: WW Microwave Intruder alarm? The first itteration of security lights outside my daughters high school used microwave sensors, which quickly disinterested with rust and we're duly replaced with PARs. __________________ -- Graham. G3ZVT

22nd Aug 2023, 12:50 am	#3
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	Re: WW Microwave Intruder alarm? Mine has an Ally and plastic casing and the microwave bit is chrome plated brass with a copper horn, all in the casing. It rarely rains here and the unit woud be in a protected area. The intruder alarm followed on from a mw audio link project, from WW 1977.

22nd Aug 2023, 11:11 am	#4
DrStrangelove Hexode Join Date: Jan 2023 Location: Neath, Port Talbot, Wales, UK. Posts: 262	Re: WW Microwave Intruder alarm? I played with the Maplin version of it which was without the tinplate horn shown in the WW article. It didn't seem overly sensitive, presumably due to the lack of the horn. It's still around here "somewhere".

24th Aug 2023, 12:06 am	#5
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	Re: WW Microwave Intruder alarm? Had another play with it yesterday, I made my own horn cutting a piece of wg16 up. Should have a gain of about 20dB. From what I gathered the module on its own was quite sensitive, mine wasn't sold with the 5dB antenna.The voltage on the mixer diode in the clear is about -15mV and varies according to what is happening in front of it. The voltages on the first two 741s (747) look about right. The voltages on the 3rd 741 are way off. I appear to have loads of AC etc. Need to dis the gunn, short the mixer and see what I'v got going on. Got loads of 741s. BTW I think I got the pcb from Maplin in Soton.