How does / can this radar wave detector circuit work?
What is the physics theory behind this?


This circuit supposedly detects radar speed traps passively. Just in case there is any confusion, it isn't part of a radar system - it's a detector that can sense the presense of (say) hand-held speed guns used by some police forces.

It "works" because at high frequencies the LM1458 op-amp is quite susceptible to EMI and this gets rectified at the input stages and a dc offset is created. It's a bit flakey in performance and was aimed at the DIYer so it isn't really anything reliable but I suppose some were made back then and may have delivered functionality.

The length of the tracks/wires that is formed in the C1-loop forms a resonant tuned circuit supposedly. Links to this circuit can be uncovered by googling "1458 radar detector" and there does appear to be a youtube video.

Here's an article from Analog Devices (MT-096 RFI Rectification Concepts) that explains the phenomena.