Photoman wrote:
We have 146.04/.64 repeater on a nearby mountain top. It worked great
for
years with a range of 100 miles or more. Since the phone company and
a pager
company installed their high power transmitters near the site of the
repeater (within 100 yards) the repeater is virtually useless. After
much
head scratching I believe that the difference in frequency of the
pager
transmitter of 600 khz is the problem but have no idea how to solve
the
problem without going to an odd split. The repeater coordinator for
this
area of Virginia won't even consider that as an option.

The equipment that we are using is excellent. The transmitter and
receiver
on the repeater are both Motorola Micor and were modified with to the

repeater frequencies by FCC 1st class licensed hams using Motorola
parts.
This is not an equipment problem. We are running a set of Wacom
cavities
which were bought new and are correctly tuned and the antenna is a
Phelps-Dodge Stationmaster. When the intermod occurs it is dependant
on BOTH
pagers transmitting at the same time. If only one pager is
transmitting
there is no problem. This may at first sound unusual but the pagers
are in
the 150 mhz band and they are exactly 600 kc apart. These transmitter
are
both 250 watts or more output.

My theory is that the 600 kc (difference of the 2 pagers) is mixing
with the
output of the repeater 146.64 and producing the 146.04 signal, the
repeater
input frequency. We are using sub-audible tone for repeater access
and as
soon as a station working the repeater drops carrier the repeater
drops. The
intermod cannot hold up the machine once the tone is removed. This
may be
happening in the antenna or hardline connectors prior to the
cavities. Every
test I have run, and there have been many, supports this conclusion.

We are not the only 2 meter repeater that has fallen victim of this
problem
and in every case we have found two pager transmitters situated 600
kc apart
near the repeater. Most of the other machines have been taken off the
air,
others just put up with it. No one has been able to solve the problem
and
many technicians have studied it.

Moving the repeater far enough away is not an option since the peak
of the
mountain is so small. Also we are using an existing tower which we
would not
have access to at other locations. The searches I have done on Google
has
turned up the stock answer of helical resonators which would apply to
2
meter radios but not repeaters. If you are familiar with the Micor
equipment
you know that the receiver has excellent helical resonators built in.

Tonight I have considered the possibility of splitting the receiver
and the
transmitter of the repeater and linking the rx signal by a 220 mhz
link. I
am hoping that by reducing the level of the 146.64 signal by 50-60 db
would
alleviate the problem. Maybe not, but I'm out of ideas. This split
would be
only about 100 yards but could that be sufficient to relieve the
problem?

Have any of you ever had this problem and solved it? Any input (pun
intended) on this matter would be appreciated.

Ken Sturgill, KC4IH
Marion VA
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Why not list the frequency of the pager transmitters here? Also, I
don't see what type duplexers that you have? Are they pass/pass,
pass/reject, what do you have?

If you think the paging transmitter may be mixing with your signal,
what about a circulator or isolator on your transmitter? I don't see
that listed in your equipment list.

You may also want to make sure that the paging transmitters have some
soft of filter cavities on their outputs.