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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