On Fri, 1 May 1998 16:20:06 -0600 John Lyles <jtml@lanl.gov> writes:
SNIP
>
>Another thing I remember is that a repeater site I worked on had a lot
>of
>probs with IMD, some coming in the back door, and a lot from rusty
>metal on
>the tower, connectors, and dirty transmitters. It was and still is a
>constant threat to the commercial and amateur operator on a heavily
>loaded
>tower site.
>
>John
I have a customer who is the NE engineer of a large paging company. They
also experienced ( caused most of it with their 250W amps ) IMD at
various sites. During one of his visits here to pick up parts we got into
a brainstorming session on the IMD and it became fairly evident that most
appeared to come from the turnbuckle to equalizer plate interface on the
Rohn 25/45/55 towers that were in use. Running various grounding wire
jumpers did not work. What did work and is now a part of all their sites
is installing large ferrite beads...the same ones that I sell to go over
RG-213....over the guy wire at the turnbuckle. Since starting the
upgrade in 1990 they have experienced no more phantom IMD and whatever
does exist can be removed by the conventional cavity filters. They
co-locate on existing towers in most cases and have to deal with lots of
RF. Site owners have also reported the elimination of problems that
existed before the pagers went on-line.
73 Carl KM1H
>K5PRO
>
>
>
>--
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>
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