# How does / can this radar wave detector circuit work?

I have difficulties to understand how the below circuit can detect radar waves by only using C1 and the lengths of its wires to IC1. Can this work? And if yes, how? What is the physics theory behind this?

This circuit uses a 1458 dual op-amp to form a radar detector. C1 is the detector of the radar signal. The first op-amp forms a current-to-voltage converter and the second op-amp buffers the output to drive the piezo transducer. R5 sets the switching threshold of the second op-amp; normally it is adjusted so that the circuit barely triggers on background noise, then it's backed off a bit. The response of the circuit may be tuned by adjusting the length of the leads on C1. For typical road-radar systems, the input capacitor's leads should be about 0.5 to 0.6 inches long.

• Odd that it uses a 9V supply, rather than the 12V readily available in a car. Jan 15 '18 at 10:33
• Car power is dirty as hell. For sensitive circuits running of a seperate battery is probablly easier than taking power from the car. Jan 15 '18 at 16:52
• @user3190797: Due to some states having laws allowing police to confiscate any radar detecting "device", you probably want it completely physically isolated from anything else you care about so that there's no question of the scope of what they can confiscate... Jan 15 '18 at 20:43