[Bobalu]

"Yeah, receivers do emit a radio signal, but not on the receiving frequency and not powerful enough to interfere with anything beyond a few feet."

Yup, back when I was a kid we used to modify our scanners so we could FM modulate the 10.7 if transmission...when you got close to a cop car they would hear what you were transmitting :-) usually we had it broadcasting what the car radio was tuned to.

Commercial FM stations use the same technique to see how many people passing by on the freeway are tuned to their station...they just listen 10.7mhz away from their frequency and if they hear a carrier that means another radio is tuned to their signal.

You can hold 2 fm radios close to one another and pick up the IF output from one on the other....just tune around and you will find it.

You can take a scanner to work and tune 10.7 away from the freq the boss's pager is at and use it as a 'Boss detector' :-) you will pick him up from 100' or so away.

Dope dealers have used pocket scanners scanning all the IF offsets the local cops use....if some plain clothes man comes near their scanner will pick up the IF output if they have a 2-way on them in recieve mode.

[cva66snipe]

Only if the scanner is not triple conversion. Triple conversion eliminates Imaging which is what you are talking about doing. On older scanners an inexperienced person may think they have found new frequencies. For example Ham operators on the 160's MHZ band with the Feds. Most older scanners though image 21.? MHZ above or below key in frequency. I think you multiply the 10.7 X 2 to get the imaging frequency. The 10.7 figured varied scanner to scanner but that was close. I have a PRO-2034 that images at 21.7 MHZ. A police call book now no longer being published :>{ explains this I understand it but can't explain it.

[ConservativeMan55]

bttt