Re: Interference on a 6 meter repeater > > That's odd that the cavity in the telemetry radio feed didn't > > change things, but it goes away when the radio is disconnected > > from the antenna.
I'm surprised how many people feel cavities (the typical cavity filter) are sure-fire cure-all medicine. After a few real war stories one learns they are not a "Guaranteed Fix". > > It could be that a parasitic diode junction is occurring > > somewhere in the antenna system, generating the IM, but > > only when the radio or cavity is just providing a DC path > > for the diode to self-bias (or perhaps the radio is even > > providing a small bias current up the antenna cable, as > > some radios do). When the telemetry transmitter comes on > > it probably swamps the parasitic diode so much it stops > > working as a diode for the duration. The problem I found was traced back into the radio itself. Didn't care to check if it was the tx or rx sections. > > p.s. was it a bandpass or notch cavity? Probably wouldn't matter in this example... cheers, s.
