At 9/25/2007 05:20, you wrote: >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?
Anything with a CPU in it could be the culprit @ 2 meters. Anytime I drive within ~200 ft. of a local "Foothill Transit" bus the squelch on my mobile radio blows open; within 50 ft., normally full quieting signals are completely captured by the noise. I suspect it's the electronic scroll sign on the back of the bus. Fortunately I haven't seen this on 440 MHz, but with faster CPUs finding their way into everything it may only be a matter of time. Bob NO6B
