Sorry for short title but the bug would not let me post with a title > 20 chars.

I need to make a simple circuit that can detect the presence of a 24.125 GHz radar beam being produced by a car speed detector display.

I don't want it in my car and I don't want to avoid being caught speeding by detecting when I'm driving into speed traps. I need to explain a little, please be patient...!

I operate a professional, tripod mounted, kerb side doppler radar speed detector (containing the transmitter, receiver and display) to measure the speed of approaching cars. The radar beam spreads out in a rough rectangle.

What I want to do is stand at various places about 150m in front of the transmitter and check if I can detect the beam so that I can align the display correctly so that it 'sees' the bit of the road I want it to (especially near hills when I need to alter the vertical angle of the display or near the end of speed limit zones where I want to avoid detecting cars outside the speed limit).

I'm thinking along the lines of the device I used to align my TV aerial, but operating at 24.125 GHz instead of the MHz region.

Anyone know of such a circuit that I could build?

 

Looks like standard K band. Radar detectors are plentiful and not very expensive. Making your own for those frequencies is not easy. Maybe new designs have been developed, but in the old days the radar detectors used microwave diodes inside tuned waveguides and synchronous detectors. One diode modulated the incoming radar signal with a few KHz and the second one was the synchronous detector driven by the same oscillator. The circuit is relatively simple, but making precise waveguide or microstrip is not.

 

http://www.ebay.com/itm/Whistler-16...=US_Radar_Laser_Detectors&hash=item4d157f0b77

$10 with shipping

 

@GopherT
Thanks but that type of thing is designed to go in a car and needs a 12v supply. I need it hand held and easily portable. I could build a 12v battery supply I suppose.

@alexfreed
Yes it is standard K band.

I did do a lot of Internet searching before coming here but many pages/posters confuse the terms. Some think Radar is the same as Lidar, even found a page on ultrasonic radar! (although I suppose its true e/m radiation does go faster than sound waves) and the term 'radar detector' is used both for a detector that utilises radar to detect things a detector OF a radar beam. I need the latter. That's why I came here for some proper advice!

Thanks to both of you, looks like the cheap speed trap car things with a external battery pack might have to be the way to go. Shame though.

 

@GopherT
Thanks but that type of thing is designed to go in a car and needs a 12v supply. I need it hand held and easily portable. I could build a 12v battery supply I suppose.

Any project you build will need a power supply. It may run off of 9 volts, if not, you could buy a 12 v power pack and charger at a hobby shop (with charger) for about $25.

 

For what you are doing, I think a signal strength meter would be a lot more useful than a mere plus/minus detector. More expensive I suppose, but perhaps worth it?

 

Many car radar detectors have LEDs to indicate the signal strength. I see no shame in using a device designed specifically to detect a presence of a radar beam to detect a radar beam. 8 AA cell battery will give you the 12 V.