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Old December 22nd 04, 02:02 PM
Dave
 
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You failed to indicated if the interference is
present when your own repeater transmitter is off.
First order of business is to eliminate the
non-offending variables. If the interference
is present with the repeater transmitter off,
then it is possible that high-level mixing
is taking place in the final amp of the paging
transmitter or another RF source in close proximity
to your repeater. If you find this is the case,
it can likely be resolved by installing a ferrite
circulator in the line of the offending transmitter.
This will keep the mixing frequency from traveling
down the feedline and entering the final amp
and mixing with another frequency to produce
the "rogue" frequency that is causing the trouble.

Hope this helps.

Good luck.


"Photoman" wrote in
:

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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