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Old March 18th 14, 01:22 AM posted to rec.radio.shortwave
Jon Danniken Jon Danniken is offline
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First recorded activity by RadioBanter: Mar 2014
Posts: 16
Default FM radio reception at ~24MHz?

On 03/17/2014 03:10 PM, matt weber wrote:

The 'front' end of many relatively low cost, wide range receivers has
very poor selectivity. The output of the Mixer stage is the SUM and
the DIFFERENCE between the local oscillator frequency and the incoming
signal. The result is when you tune a frequency, you are really tuning
to two different frequencies. The difference between one signal and
the IF and the Sum of another signal and the IF, Usually there is some
sort of pre-selector, bandpass filter or semi-tuned RF amplier that
effectively blocks the unwanted frequency, so there is no energy in
one of the two possibly tuned frequencies

For example if you have a conventional FM receiver, traditionally the
Intermediate frequency is 10.7 Mhz. So if you tuned the receiver

Another strategy is to 'up convert' instead of down convert. This puts
much more spectrum between the sum and difference frequency.

All that your experience says is that SDR probably has poor front end
selectivity.


Thanks Matt.

Jon