Hi Colin, it's hard for me to explain how it works as I barely understand it
myself.  I know that right after the rf pre-amp the rf signal is sent into a
mixer along with the frequency of the local oscillator (LO).  The LO is
tuned to 10.7 MHz lower than the signal you want to receive, so in the mixer
you get the sum and the difference of the LO and the rf.  The 1st IF is
tuned specifically to pass the difference of the rf and the LO which is a
constant 10.7 MHz.  When you hold 2 receivers close together the LO's and IF
freqs all get mixed up and you get the sums and differences of several
frequencies.  This explains why you can tune the wide-band receiver either
10.7 above or below the analogue receiver.

Here's some good reading: http://www.dbugman.com/handbook/tscmh5.html
73, Ken -N5SWR


-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of Colin McDonald
Sent: Wednesday, January 24, 2007 2:01 AM
To: [log in to unmask]
Subject: Re: Using HT as tuning aid for FM radio


I never tried that trick until now...works absolutely great.
Using an old short wave receiver with FM in it, and putting the ict90 on
wide FM, i could actually listen to the audio clearly on the HT when the
receiver was tuned to a station 10.7MHZ down from the HT's receive
frequency..
What exactly causes this?
Presumably the receiver is resonating at that frequency and causing some
sort of signal to be inducted into the HT?
I didn't test how far away from the receiver I could go before losing the
audio on the HT....perhaps tomorrow.
73
Colin, CF6BKX
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