On Mon, 5 Apr 2010 13:36:45 +1000, "Phil Allison"
wrote:

The AGC makes AM reception possible while using an 10.7 MHz FM IF strip
..... Phil

Amazing. You sorta figured it out. Welcome to the 21st century.

I'll assume by "AM reception" you mean receiving DAB or DRM
broadcasts, which are simultaneously both AM and FM in the short wave
(2-30Mhz) bands. That will work. Of course, with an all digital AM
receiver, and a rather limited AGC circuit (one PIN diode with only
25dB of AGC range), cramming 33 to 40dB of RF pre-amplifer gain into
the front end will run it into overload or blocking.

See the NXP TEA5777 data sheet at:
http://www.kako.com/neta/2007-006/tea5777.pdf
Table 45 on Pg 37. AM RF AGC range = 25dB. Unfortunately, there are
no FM RF AGC specs on Table 44 on Pg 34. My guess(tm) is that the FM
and AM AGC ranges are similar as they use similar circuitry. With
only 25dB of AGC, any moderately strong signal at the beginning of the
AGC curve, will be amplified into the overload region if 33 to 40dB of
RF gain is added.



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