From: john@zygot.ati.com (John Higdon)
Subject: Re: Cross-talk between FM stations
Originator: wdp@gagme
Organization: Green Hills and Cows
Date: Sat, 12 Dec 1992 08:21:42 GMT

netxcom!jwc%netex.netx.com@uunet.UU.NET (Jeffrey W. Comer) writes:

> I am considering a complaint the the FCC, but before I do, I am wondering if
> I should investigate further. Let me say I am not an engineering type, though
> I can understand most of what they say. Or am I just being a little too anal?

The FCC should be your last stop. My first comment is one that I give
everyone that calls my station with such a complaint: If this was a
station problem, don't you think that the stations involved would be
innundated with complaints? The chances are excellent that the problem
is in your radio (images), re-radiation from some external object in
your local area, or some interaction with another local receiver.

It is the nature of FM reception that when there are two stations on the
same frequency, the capture effect of the receiver excludes the weaker
of the two. The capture ratio of a typical receiver is on the order of
1 decibel. This means that if one is only slightly stronger than the
other, the weaker one will be excluded, which pretty well rules out the
possiblility that one of the stations has undesirable products on the
other's frequency.

The only other station problem would be the matter of
"intermodulation". This is where the signal of one station travels down
the antenna system of another, mixes in the second station's
transmitter, and is then rebroadcast by the second station on a third
frequency. This is unlikely, particularly if the stations' transmitters
are not co-located.

>   portable - Sony ICF-7600.
>   auto - Blaupunkt Boston.

I think the ball is in your court. Both of these receivers are
notorious for their susceptibility to "imaging", which is an
overloading of the front end. The resultant internal harmonics cause
the station to appear at multiple points on the dial, even on top of
other stations.

It is a simple matter to check with a friend somewhere and see if he
experiences the same problem. If the fault lies with the stations
involved, then anyone should be able to witness the difficulty you
describe. If what you hear is the result of difficulty at either or
both stations, it will appear on any radio, anywhere. If
it is clean on so much as one radio, it is not the station's problem.

One more thing. Always work with the stations before you call the FCC.
No engineer wants a dirty signal and no station owner wants an
interference problem. No broadcaster would intentionally step on the
channel of a brother in the cloth. Radio stations are not a bunch of
gangsters that must constantly be kept in check by the Feds. Do you
call the police if a clerk inadvertantly short-changes you at the
store?

The station engineer is intimately familiar with his signal and its
relationship to the others in the area. If he tells you that there is
no problem (from his perspective), then you need to look to your own
surroundings and equipment.

-- 
 John Higdon  |   P. O. Box 7648   |   +1 408 264 4115     |       FAX:
 john@ati.com | San Jose, CA 95150 | 10288 0 700 FOR-A-MOO | +1 408 264 4407

Newsgroups: rec.radio.broadcasting