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.