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 ~
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www.poppyrecords.co.uk