On Mon, 5 Apr 2010 12:26:26 +1000, "Phil Allison"
wrote:

"Jeff Liebermann Radio Ham ****wit "
The FM tuner might have an AGC section. This is required for direct
digital receivers that have an A/D converter in the front end of at
the IF frequency. The AGC is necessary to use the entire range of the
A/D. These usually have a limited dynamic (amplitude) range and are
easily overloaded. When amplified, this would cause a strong signal
to disappear as it runs out of head room.

** Massive pile of ******** !!!

You're making me hungry:
http://en.wikipedia.org/wiki/Rocky_Mountain_oysters

FM signals are not affected by amplitude limiting - cos limiting is just
what the IF stage is designed to do.

You forget that the limiter stage has to handle only one FM signal.

** You assume wrongly.

The discussion is about possible overload in an antenna amplifier

** The point at issue was that in the para just above my comment.

I hate to bring you kicking and screaming into the 21st century, but
many of todays FM broadcast systems are not pure FM modulation.
HD_Radio and DAB use a combination of AM and FM modulation and
therefore require an AGC to be properly demodulated.
http://en.wikipedia.org/wiki/HD_Radio
http://en.wikipedia.org/wiki/Digital_Audio_Broadcasting
If the OP's unspecified model tuner was an HD Radio type of tuner, AGC
overload is certainly a possibility.

However, there are problems even with traditional pure FM systems. The
all digital DSP FM tuner chips require an AGC to maximize the dynamic
range of the A/D converter driving the DSP. I posted this, with
examples, in a previous message. This is also what I was talking
about in the above paragraph. Perhaps you missed it:
http://groups.google.com/group/sci.electronics.repair/msg/cd33a3e5df4b94a3

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558