>>Generally the gauge is a reading of the AGC (automatic gain control)
>>level being applied by the radio's IF. There are many other ways to derive
>>this signal, but this is the most common one.
>How is this AGC level derived, and how is it compared to the signal?
Nothing fancy - the AGC circuit is typically just a simple rectifier followed
by a RC time constant. The resulting level goes to your meter and is fed
back into the IF at a point where changing a bias affects the gain. If
there's a "skip over static" function in a digital tuner, it's typically
done by comparing the AGC level with a fixed voltage (possibly settable
with a pot somewhere.)
There are fancier methods of detecting the presence of a signal if you
know something specific about that signal. For instance, if you know that
it's a FM stereo broadcast, you can look for the FM subcarrier.
--
Tim Shoppa Email: shoppa_at_trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
7328 Bradley Blvd Voice: 301-767-5917
Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Fri Apr 16 1999 - 16:49:55 BST