Our local club recently installed a 2 meter repeater on a water tank adjacent
to a cell site. Two cell towers are serviced by four buildings housing
equipement, and we are having some desense due to noise pickup on the antenna.
Running an iso-tee we found that our GE Mastr II receiver with GE preamp shows
.6 uV for 12 dB SINAD using a dummy load in place of the antenna (.2 uV direct
to the receiver bypassing the duplexer). With the antenna connected we see a 2
uV sensitivity for 12 dB SINAD.
These readings are the same, with the repeater transmitter (40 watts) keyed
or unkeyed.
The noise floor is really decreasing the utility of the new repeater. The
noise source seems to come and go as a quiet signal on the repeater input can
become suddenly noisey, and vice versa - a noisey signal can become suddenly
quiet.
I hear the air conditioning units in the cell site buildings cycling and
wonder if they might be the cause of the noise? Our antenna is only about 40
feet above the ground (at 7400 ft) while the cell antennas are at about 100 ft.
So we are much closer to the cell site equipment buildings than the cell
antennas.
Two uV for the receiver sensitivity sure does limit the usefulness of the new
repeater -
Anyone have any thoughts?
73 - Jim W5ZIT
[EMAIL PROTECTED] wrote:
I am having some receive problems on my repeater and I am
thinking that it might be desense. I am on 2M running a
MASRII repeater with a Decibal Products band reject 6 can
duplexer.
While I can key the repeater from a pretty good distance
the audio that makes it through the repeater drops off
pretty quickly. I just had the duplexers tuned and they
are tuned very well.
So on to my question. If I were to take and seperate the
recv cans from the xmit cans and run to 2 seperate
antennas would that mess up the duplexer tuning? will 20'
of vertical seperation plus the cans and the fact that I
would be running through seperate cable, make a
difference?
Thanks,
Vern
KI4ONW
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