Why would an FM signal amplifier make some signals disappear

On Tue, 30 Mar 2010 19:03:42 -0500, "William R. Walsh"
<newsgroups1@idontwantjunqueemail.walshcomptech.com> wrote:


The amplifier in question is a Radio Shack 15-321. It's a two-in-one unit,
with two pieces. One goes on the antenna and has an adjustable amplification
level that is set via a potentiometer on the indoor unit. The other is
internal to the indoor unit and offers a fixed boost that can be turned on
or off. Power is supplied to both through the indoor unit.
Click to expand...
<http://www.radioshack.com/product/index.jsp?productId=3770519>
(Read the 2nd product review)

40dB of gain from VHF to UHF TV bands (54 to 700Mhz)? That's a bit
much. Oh, the box says 33dB. A bit better, but still too much gain.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS
 
In message <81go8fFhiU1@mid.individual.net>, Phil Allison
<phil_a@tpg.com.au> writes
"Jeff Liebermann Radio Ham Fuckwit "

One guess(tm) is that the Radio Shock amplifier is rather noisy. The
additional noise generated by the amplifier is stronger than the
previously weak signals. If really awful, weak signals will be
totally lost in the noise.

** Bollocks.


The Radio Shock amplifier might be oscillating, thus creating the
in-band strong signal necessary to create the blocking effect.

** More bollocks.

Results would be very bad all over the band.


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 BOLLOCKS !!!

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

FUCKWIT !!!

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

"Jeff Liebermann Radio Ham Fuckwit "

One guess(tm) is that the Radio Shock amplifier is rather noisy. The
additional noise generated by the amplifier is stronger than the
previously weak signals. If really awful, weak signals will be
totally lost in the noise.

** Bollocks.


The Radio Shock amplifier might be oscillating, thus creating the
in-band strong signal necessary to create the blocking effect.

** More bollocks.

Results would be very bad all over the band.


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 BOLLOCKS !!!

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

FUCKWIT !!!

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

** You assume wrongly.


The discussion is about possible overload in an antenna amplifier
Click to expand...

** 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
 
On Mon, 5 Apr 2010 12:26:26 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"Jeff Liebermann Radio Ham Fuckwit "
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 BOLLOCKS !!!
Click to expand...
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.
Click to expand...
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 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, But Case & LIAR "
" Phil Allison "

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 BOLLOCKS !!!

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


I hate to bring you kicking and screaming into the 21st century, but
many of todays FM broadcast systems are not pure FM modulation.
Click to expand...
** Totally irrelevant to the material posted above.

You are ONE desperate fucking LIAR !!


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.
Click to expand...
** More BOLLOCKS.

All you ever posted was you own WRONG opinion.

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



...... Phil
 
On Mon, 5 Apr 2010 13:36:45 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

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


One guess(tm) is that the Radio Shock amplifier is rather noisy. The
additional noise generated by the amplifier is stronger than the
previously weak signals. If really awful, weak signals will be
totally lost in the noise.
Click to expand...
** Bollocks.


The Radio Shock amplifier might be oscillating, thus creating the
in-band strong signal necessary to create the blocking effect.
Click to expand...
** More bollocks.

Results would be very bad all over the band.


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.
Click to expand...
** 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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