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QRM on our 2m repeater is back again! This is an old problem, and it was solved previously. Now it's back! The QRM is so bad that I find it a pain to monitor the band. Using my spectrum analyzer with a preamp preamp infront, I had a look at the squelch tail signature of this QRM. It looks exactly as that from a bona fide 2m transmission from our repeater. Therefore, I conclude that the QRM could due to one of the following: · Intermod in the front end of our repeater. · Our repeater is repeating intermod which is being received on its Rx frequency. I was grumbling about this QRM to my ham friend Darryl 9V1DE, and he asked me to have a listen to the following frequencies, whenever I hear the QRM from our repeater: F1=142.925 MHz F2=143.975 MHz True enough, the QRM came whenever there is traffic on F1 and F2. 2F2-F1 = 145.025 MHz, which is our repeater’s Rx frequency BINGO! I have made a movie on the QRM and you can find them here: The MPT1327(?) control channel sounds like this. For those who are technically inclined, here is a very practical and easy to understand article: Lloyd Butler VK5BR on Intermod If this QRM is due to intermod at the front end of our repeater, then what baffles me is how 3rd order intermod can happen to the repeater when there is a sharp duplexer between its front end and the antenna. I have been listening to the repeater's Rx frequency of 145.025 MHz for 2 days and did not hear a single instance of QRM. Maybe the Rx at my location is poorer that at the repeater, or the repeater’s duplexer is out of tune / defective.
What’s the buzz?
One evening, my DXing was interrupted by an incessant buzzing QRM. Since power line modem QRM is a current hot topic, I immediately suspected that it was from my neighbour’s power line modem. After some sleuthing, I discovered the embarrassing source here at home…
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