In message , Phil Allison writes
You forget that the limiter stage has to handle only one FM signal. The discussion is about possible overload in an antenna amplifier, passing lots of individual FM signals. Despite being FM, nasty things are likely to happen.
-- Ian
"Ian Jackson" Phil Allison
** You assume wrongly. ** The point at issue was that in the para just above my comment.YOU failed to comprehend the normal usenet posting method and the particular context.
FOAD.
.... Phil
You're making me hungry:
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.
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:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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:
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 jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
"Jeff Liebermann Radio Ham Fuckwit & LIAR "
** Bollocks.** More bollocks.
Results would be very bad all over the band.
** Massive pile of BOLLOCKS !!!FM signals are not affected by amplitude limiting - cos limiting is just what the IF stage is designed to do.
FUCKWIT !!!
.... Phil
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