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Old September 8th 06, 09:08 PM posted to rec.radio.amateur.homebrew
AndyS AndyS is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 119
Default Intermediate Frequency


Roy Lewallen wrote:

I believe that what you said is true, but only for AM. What other kind
of modulation requires better frequency accuracy from a direct
conversion receiver LO than from a superhet LO? I believe that only a
small fraction of today's amateurs are interested in AM reception, but
of course it's the bread and butter of the SWL and BCL.

Roy Lewallen, W7EL


Andy responds

I don't disagree with anything you've said. However , i've
found it a lot easier to make the final frequency adjustments
in a superhet since it can be done at a lower frequency.
Trying to sync up at 915 is more challenging than at 455 khz,
obviously. And for systems like FSK and SSB, you gotta
do it somewhere..... And with FM, since the beat formed
by the carrier depends on the modulation index of the
received signal, getting rid of it can be squirrelly.....

Like youself, I've built both types , both as home projects,
and as commercial products, for a long long time. In the
DC versions, if I use I/Q and combine them to form the
audio, the AGC is the same as with superhet SSB. And I generally
use PIN diodes before the front end for the first AGC stage...
But, that's just my own preference.....

Andy W4OAH