Hello all...

So I was putting up an FM antenna recently and got the idea that using a
signal amplifier might be a good idea, as the output would go to two tuners,
one of which is somewhat "deaf" in terms of sensitivity.

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.

What I've noticed is that some stations just disappeared from the dial after
installing the signal amp. This is not a big deal, the amp works well
otherwise and I'm not missing the stations that don't come in. The user's
guide points this out as being a possible problem, and it says that the only
solution is to completely remove the amplifier. What it doesn't say is "why"
and that is what I would like to know. By the way, missing stations are not
confined to any one area of the FM band.

William

In article ,
William R. Walsh m wrote:

What I've noticed is that some stations just disappeared from the dial after
installing the signal amp. This is not a big deal, the amp works well
otherwise and I'm not missing the stations that don't come in. The user's
guide points this out as being a possible problem, and it says that the only
solution is to completely remove the amplifier. What it doesn't say is "why"
and that is what I would like to know. By the way, missing stations are not
confined to any one area of the FM band.

I suspect a phenomenon often referred to as "strong-signal
desensitization", a.k.a. "desense".

It can occur when you have a mix of strong and weak signals coming
into the system through the antenna. If you stick an amplifier into
the equation, it amplifies both the strong and the weak signals equally.

This can cause problems, if the signals involved are strong enough to
overload either the amplifier itself, or the "front end" in the FM
tuner/receiver. What happens, is that the strongest signals actually
push some stage of the tuner (or the amplifier itself) into saturation
or "clipping", and the RF or IF waveform becomes badly distorted.
When this happens, the circuitry can no longer respond to the
lower-strength signal at all, and the signal effectively "disappears".

By analogy: consider an old-style vinyl record, with the signal being
molded into the record in the form of a groove. Consider a signal
which has both a low-frequency component (bass) and a high-frequency
component (treble) at the same time. As long as they're of roughly
the same amplitude, the shape of the wiggles in the groove will be the
sum of the wiggling that you'd get from the low-frequency signal along
and the wiggling that you'd get from the high-frequency signal alone.

If the high-frequency signal is weaker (smaller wiggle amplitude),
things still work OK, as long as the total signal isn't too high.

Now, try turning up the amplitude of the whole signal a lot - say,
10:1 or so (20 dB). The low-frequency wiggle is so broad that it
actually slams the playback stylus all the way to the edge of its
travel in the cartidge much of the time... the stylus can't go any
further. For all of this time, when the stylus is jammed against its
limit stops, it can't wiggle at all in response to the weak
high-frequency signal. The playback system is now "de-sensitized" to
the weaker signal... it's not strong enough to overcome the saturation
effects of the stronger signal.

This is probably what's happening in your situation. You have some
strong local FM signals, and the amplifier is boosting them up so much
that they are "jamming the stylus" in your FM tuner.

In really severe cases, a strong local transmitter can even
saturate and desensitize the amplifier itself... clobbering *all* of
the desired FM signals. I had this sort of problem with a TV
redistribution amplifier... my 2-meter amateur radio transmissions
saturated it and wiped out all of the TV signals. My wife was
unhappy... and I had to find a specialized 2-meter notch filter to
keep the interfering signal out of the TV coax.

This sort of situation is relatively common, and it doesn't always
have to involve an amplifier. Some 800 MHz public-safety (e.g. police
and fire) radio systems have had desensitization problems, due to
strong cell-phone-tower transmissions on nearby frequencies. This has
been one reason for the "push" to digital TV... because it allowed the
700 MHz frequency band to be freed up, and some portions of it are
being allocated to public-safety users so they can move their
frequencies away from the desense-causing cellphone signals.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Tue, 30 Mar 2010 17:27:27 -0700, (Dave Platt)
wrote:

In article ,
William R. Walsh m wrote:

What I've noticed is that some stations just disappeared from the dial after
installing the signal amp. This is not a big deal, the amp works well
otherwise and I'm not missing the stations that don't come in. The user's
guide points this out as being a possible problem, and it says that the only
solution is to completely remove the amplifier. What it doesn't say is "why"
and that is what I would like to know. By the way, missing stations are not
confined to any one area of the FM band.

I suspect a phenomenon often referred to as "strong-signal
desensitization", a.k.a. "desense".

That's certainly a likely possibility, but I have a different theory
or three.

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.

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

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.


--
Jeff Liebermann
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 ****wit "

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.

** ********.


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

** More ********.

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 ******** !!!

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

****WIT !!!




..... Phil

It would be interesting to stick a spectrum analyzer at various points in
the system -- starting at the unamplified antenna signal and see what's
going on.

William R. Walsh m
wrote:

Hello all...

So I was putting up an FM antenna recently and got the idea that using a
signal amplifier might be a good idea, as the output would go to two tuners,
one of which is somewhat "deaf" in terms of sensitivity.

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.

What I've noticed is that some stations just disappeared from the dial after
installing the signal amp. This is not a big deal, the amp works well
otherwise and I'm not missing the stations that don't come in. The user's
guide points this out as being a possible problem, and it says that the only
solution is to completely remove the amplifier. What it doesn't say is "why"
and that is what I would like to know. By the way, missing stations are not
confined to any one area of the FM band.

Is there a reflection in the feeder from mis-match? That would cancel
some stations and the null would be quite sharp and deep.

Has anyone previously tried to use the cable to feed two sets and
installed a hidden junction box somewhere along the line? Is the cable
connected in the correct way to the units, with the screen properly
clamped? Is the cable of the correct characteristic impedance for the
pre-amplifiers (50-ohm or 75-ohm)?

You could try cutting an inch or two off the feeder (if you have enough
to spare) and see if the missing stations come back and others
disappear.

Another possibility is a balance/unbalance problem at the head
amplifier. If you have a spare ferrite ring, try slipping it over the
cable near the input or the output of the head unit and see if that
makes any difference.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

" William Sommer****** "

It would be interesting to stick a spectrum analyzer at various points in
the system -- starting at the unamplified antenna signal and see what's
going on.


** Wot do you ****in' expect - ****** ??

The big signals are bigger.

The little ones get bigger too.



...... Phil

"William I. Walsh"
m wrote
in message
...
Hello all...

So I was putting up an FM antenna recently and got the
idea that using a
signal amplifier might be a good idea, as the output would
go to two tuners,
one of which is somewhat "deaf" in terms of sensitivity.

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.

What I've noticed is that some stations just disappeared
from the dial after
installing the signal amp. This is not a big deal, the amp
works well
otherwise and I'm not missing the stations that don't come
in. The user's
guide points this out as being a possible problem, and it
says that the only
solution is to completely remove the amplifier. What it
doesn't say is "why"
and that is what I would like to know. By the way,
missing stations are not
confined to any one area of the FM band.

William

Could the amplifier possibly have and FM trap built in? This
is common in many amplifiers designed for TV use. A quick
look at the user manual says there is a switchable trap on
this model. How is the switch set?

David

On Mar 31, 4:29*am, "William Sommerwerck"
wrote:
It would be interesting to stick a spectrum analyzer at various points in
the system -- starting at the unamplified antenna signal and see what's
going on.

uh, most HP spectrum analyzers had a 35+ dB noise figure, and you are
trying to 'see' the NF for RadioShack's amplifier, right, probably 2
to 3.5 dB NF?

So, a quick check that the cause of losing stations was due to
increasing the noise floor can be checked by verifying that all the
lost stations were weak stations to begin with.

It would be interesting to stick a spectrum analyzer at various
points in the system -- starting at the unamplified antenna
signal and see what's going on.

Uh, most HP spectrum analyzers had a 35+ dB noise figure...

I didn't know it was that bad.

On Mar 31, 11:58*am, "William Sommerwerck"
wrote:
It would be interesting to stick a spectrum analyzer at various
points in the system -- starting at the unamplified antenna
signal and see what's going on.
Uh, most HP spectrum analyzers had a 35+ dB noise figure...

I didn't know it was that bad.

It is easy to take the specs and calculate.

For example, what's the one you were planning on using?

In article ,
William Sommerwerck wrote:

It would be interesting to stick a spectrum analyzer at various
points in the system -- starting at the unamplified antenna
signal and see what's going on.

Uh, most HP spectrum analyzers had a 35+ dB noise figure...

I didn't know it was that bad.

I don't know about the specific number, but I believe that in general
spectrum analyzers make quite poor receivers (for weak-signal work at
least). They're designed more for bench-work, where signals are
relatively strong and there's a real need to ensure that strong-signal
intermodulation doesn't occur.

It's not a trivial job to make a receiver front-end with a really low
noise filter, enough gain to take advantage of it, the ability to
withstand really strong signals without overloading, and a wide
frequency range.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Wed, 31 Mar 2010 21:59:19 +1100, "Phil Allison"
wrote:

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 ******** !!!

See:
http://www.st.com/stonline/books/pdf/docs/8933.pdf
Note the AGC in the front end of the FM section (running a PIN diode).
The idea is to keep the output signal level within the maximum dynamic
range of the DSP A/D that follows this chip.

NXP also makes an AM/FM front end chip, the TEA5777 (which seems to
have disappeared from the NXP web pile.
http://www.kako.com/neta/2007-006/tea5777.pdf
See section 8.2.1 which proclaims:
An RF AGC circuit prevents the mixer and IF
filter from overdrive conditions.



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

Hi!

I suspect a phenomenon often referred to as "strong-signal
desensitization", a.k.a. "desense".

I wondered if something like this might be taking place. But I was not
at all sure.

Something curious happened last night. I went over and turned the
stereo receiver on. By complete chance, I ended up tuning the receiver
to one of the stations that had disappeared from the dial. Its
automatic seeking function stopped on the station.

To my complete surprise, the station was coming in perfectly. So too
were several other stations that I had previously noted to be gone.

I checked the amplifier, it was still plugged in and seemed to be
doing its thing. The HD radio tuner also picked up the stations.

I am unsure what changed...could it have been something in the
atmosphere or even space affecting this? Weather has been sunny and
warm, last night's sky had a full moon (maybe that's an idea! g) and
some cloud cover.

William

Why do you feel that anyone could believe you when your arguments
quickly degenerate into profanity?

William

Hi!

Is there a reflection in the feeder from mis-match?

I am not sure how I would know. There is a matching transformer way up
at the top of the antenna that goes from its connections to the
coaxial cable. This in turn feeds into the input of the amplifier.

Coming out of the signal amp is another length of coaxial cable, this
one 25 feet long. This goes to a grounding block and then on into the
building with another twenty five feet or so of coax, where it
connects to the "power" unit.

I'm not sure if the grounding block is in the "right" place but it is
connected and properly grounded. I don't know that it would make a
difference. I tried temporarily removing it and noticed no change.

The "power" unit has a built in splitter. A stereo receiver is
connected to one end with approximately six feet of coaxial cable. The
other output goes to an HD Radio tuner. Both have 75 ohm connections.

Has anyone previously tried to use the cable to feed two sets
and installed a hidden junction box somewhere along the line?

Definitely no. I ran all of the cable for this, so there is nothing in
it that I would not know about.

*Is the cable connected in the correct way to the units, with the
screen properly clamped?

I believe I've done this correctly, by following the printed
instructions.

*Is the cable of the correct characteristic impedance for the
pre-amplifiers (50-ohm or 75-ohm)?

The instructions that came with the amplifier don't talk about this in
any great detail. The obvious thing to do (to me at least) was to use
75 ohm cable. I would have to think that if some special cable were
required, the instructions would talk of it.

William

Hi!

Could the amplifier possibly have and FM trap built in?

Yes, it does. It is located in the outdoor unit and is switchable. I
was sure that I had switched it off, so I went up and looked. It's
definitely off.

I checked and turning it on basically kills all FM reception, so I'm
sure the switch is working.

William

William R. Walsh wrote:

Hi!

Is there a reflection in the feeder from mis-match?

I am not sure how I would know. There is a matching transformer way up
at the top of the antenna that goes from its connections to the
coaxial cable. This in turn feeds into the input of the amplifier.

Coming out of the signal amp is another length of coaxial cable, this
one 25 feet long. This goes to a grounding block and then on into the
building with another twenty five feet or so of coax, where it
connects to the "power" unit.

I'm not sure if the grounding block is in the "right" place but it is
connected and properly grounded. I don't know that it would make a
difference. I tried temporarily removing it and noticed no change.

The "power" unit has a built in splitter. A stereo receiver is
connected to one end with approximately six feet of coaxial cable. The
other output goes to an HD Radio tuner. Both have 75 ohm connections.

Has anyone previously tried to use the cable to feed two sets
and installed a hidden junction box somewhere along the line?

Definitely no. I ran all of the cable for this, so there is nothing in
it that I would not know about.

*Is the cable connected in the correct way to the units, with the
screen properly clamped?

I believe I've done this correctly, by following the printed
instructions.

*Is the cable of the correct characteristic impedance for the
pre-amplifiers (50-ohm or 75-ohm)?

The instructions that came with the amplifier don't talk about this in
any great detail. The obvious thing to do (to me at least) was to use
75 ohm cable. I would have to think that if some special cable were
required, the instructions would talk of it.

Sounds as though mismatch isn't the problem then (unless something funny
is happening in the grounding block).

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

In article , Jeff Liebermann wrote:
On Tue, 30 Mar 2010 17:27:27 -0700, (Dave Platt)
wrote:

In article ,
William R. Walsh m wrote:

What I've noticed is that some stations just disappeared from the dial after
installing the signal amp. This is not a big deal, the amp works well
otherwise and I'm not missing the stations that don't come in. The user's
guide points this out as being a possible problem, and it says that the only
solution is to completely remove the amplifier. What it doesn't say is "why"
and that is what I would like to know. By the way, missing stations are not
confined to any one area of the FM band.

I suspect a phenomenon often referred to as "strong-signal
desensitization", a.k.a. "desense".

That's certainly a likely possibility, but I have a different theory
or three.

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.

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

I have seen this effect. It could also cause multiple frequencies being
generated. Sometimes adding core chokes around the in and
the out of the amp, can help. And you can reduce gain.

greg


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.

On Tue, 30 Mar 2010 19:03:42 -0500, "William R. Walsh"
m 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.

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
# http://www.LearnByDestroying.com AE6KS

In message , Phil Allison
writes

"Jeff Liebermann Radio Ham ****wit "

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.

** ********.


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

** More ********.

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 ******** !!!

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

****WIT !!!

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

"Jeff Liebermann Radio Ham ****wit "

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.

** ********.


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

** More ********.

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 ******** !!!

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

****WIT !!!

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.

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"
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

"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 ******** !!!

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.

** Totally irrelevant to the material posted above.

You are ONE desperate ****ing 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.

** More ********.

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"
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