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January 24, 2012


John Dunn

Typo! That middle line should read "....just for the sake of visual convenience."

Sorry about that.

george storm

This is a method that works in principle, but the described requirement for small delay would appear to present a conflict between linearity and circuit noise.
On which subject: with a delay of 10-ns, the signal at the 17 MHz end of the range would already be reduced below half that expected from the initial slope.
Things are somewhat better if we shift the 14-MHz range to sit symmetrically around 100-MHz (i.e. from 93 and 107 MHz). The signal reduction relative to peak slope is "only" 10%.
Nevertheless, linear FM systems typically reduce the mudulation range to below 5% and use resonant detectors - both for practicality and to reduce the noise

John Dunn

Actually, this item, like all of the others I've posted, was put to practical use. In this case, I needed to make an FM demodulator that was as idiot-resistant as possible and as easily constructed as possible. This was it.

Tom Christian

That's interesting. I'm interested in radio receiver
design, but I've found that many books give little
information on practical circuits for demodulation.
Frequently the demodulator is simply depicted as a
But now what about the 10 nS time delay depicted in your
diagram. How might that be implemented in circuitry?
What other types of FM demodulators are there?

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