[Biggles]

We had problems at one of our main-scheme sites in Lancashire with a low band transmission breaking through onto our main receivers. A couple of day's work with a spectrum analyser and a lot of waiting around for the offending transmitters to flash up (why do they remain eerily quiet when you are on site?) proved one to be on exactly half our receive frequency with a lovely second harmonic splattering everywhere. A quick call to the DTI or whoever it was before Ofcom and job sorted. Co-sited high power paging transmitters always seemed to find a way into your receivers without having to use extra bandpass filters in line too. We had a strange one up in north Northumberland with one of our microwave link PSU's alarming randomly. I had the task of sitting watching the thing one day after checking everything was fine and normal on the PSU. After a while, on the hour, every hour, an alarm came up just long enough to trigger the supervisory. A little bit of poking around discovered some form of data transmitter lashed inside a cabinet (why did people always leave the cabinet key on top of the rack?) with a rubber duck whip antenna on it. The RF was breaking into our alarm circuitry and causing spurious triggers. Another call to the DTI soon had that one stopped too.
Alan.