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[SOLVED] Detect FM radio frequency thru Power and Ground

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rarri77

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Hello,

What is the best means to detect the frequency of a radio that is powered on and tuned to a particular frequency (ex 95.5 mhz) thru only the power and ground cables, if it is even at all possible. I dont necessarily need the exact frequency the radio is tuned to in case of mixing, but what type of information can be garnered at the very least.

Thx
 

The question is ambiguous in several regards. I guess you mean:

- estimate the tuned frequency of a FM radio receiver by it's LO leakage
- tap the radiated/conducted oscillator leakage somewhere at the power supply lines

I presume it won't work unless you're tapping the signal quite near to the receiver or you are in the middle of nowhere with no interfering RF around.

For a serious consideration specify the receiver type and whole setup.
 

Why do you want to do this? Are you a spy? Detecting the LO frequency only works if you know the IF.
 

"estimate the tuned frequency of a FM radio receiver by it's LO leakage"

I would like at best to estimate the tuned frequency. A standard fm radio receiver is the setup.
 

Why is this a inappropriate question to ask? With a known IF, how would you go by detecting the LO?
 

With a known IF, how would you go by detecting the LO?
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I presumed so far that you know how a "standard fm radio receiver" works and which LO frequency could be expected on your example. There are of course the alternatives of up- or down conversion. I would expect 10.7 MHz and down conversion for standard receivers.

Exploiting the radiated spurious emission limits, LO leakage can be up to 2 nW respectively 150 µV/m received field strength at 3 m distance. That's quite a lot and can be detected with a spectrum analyzer in the vicinity, if no other RF noise sources are present.

A quality receiver can have much better suppression of LO leakage and might be not detectable.
 

Thanks for the reply.

I havent had much luck detecting radiated over the air emissions, hence the reason for detecting thru power and ground. Better phrased, how does the signal path flow after mixing and best method for detection?
 

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