general RFI - RFI Forum at eHam.net

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general RFI	Reply
by VK4TJF on September 3, 2009	Mail this to a friend!
i have never really bothered to ask i have just accepted it as a part of radio what causes for lack of a better term "birdies" on the bands or tones on specific frequencies? these tones are very easy to pick up on CW mode.

RE: general RFI	Reply
by N3OX on September 3, 2009	Mail this to a friend!
Anything that relies on a stable oscillator for timing, basically. Some of them are even internal to your radio... mixing products that the designers couldn't get entirely out of the bands... ;-) But there are a lot of electronic devices that need some stable frequency reference... that and its harmonics (or subharmonics if it gets divided down while in use) can be heard as stable carriers. Less stable oscillators, like those in switching power supplies, tend to be "rough" and also drifty because their frequency is not very critical. But timing signals for digital equipment need to be better than that, so they will end up in narrow bandwidths. A typical "TTL can" clock oscillator is maybe +/-10ppm, and variation within that is probably going to be pretty slow drift... so even if you're listening to a higher harmonic you might not notice the drift unless you go back and check it periodically. 73 Dan

RE: general RFI	Reply
by W2MV on September 15, 2009	Mail this to a friend!
I can deal with a few, discrete, annoying "birdies." The main problem for me is wideband RFI which ruins reception on an entire band. As an example, the PC I use for ham work generates an annoying signal at 14.029 MHz...very stable. That is not too much of a problem unless, of course, the DX is right on that freq! Various other devices, of particular note switching p/s's and battery chargers can kill a whole band! Good luck.

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