RF Interference troubleshooting SBC DSL FAQRF Interference troubleshooting (#1982)
Preface: There are many, many things that cause interference, and if you find the (suspected cause) of the problem, use some tact! There are many reasons for devices becoming unwanted receivers, and both sides may be "at fault". Both sides will have to work for a successful completion of the problem. Don't approach this with an "Attitude" or you'll have an Attitude all by yourself!
1. Dimmers... There are so many, with each company making them as inexpensive as possible, they reduce or remove the RFI filters to keep costs down, profits up. You can usually use a portable AM radio tuned to the upper band edge at an unoccupied station to be used as an RFI sniffer. It will sound like a raspy buzzing. Work around: Unplug it and replace with one that has better RFI suppression (Good Luck!)
2. Power transformers (Com ED)
Use the same RFI Sniffing procedure (Car or walkaround), then call and complain.
3. Electric devices (irons, frypans, heat lamps, etc). The noise they generate as they turn on, turn off, is considerable. AM radio (Powered off AC) will lead you right to it. Christmas light flashers will do same thing to a lesser extent.
4. Transmissions (Ham, CB, Cellphone, etc.) These are harder to find. Watch the modulation characteristics:
Is it a solid pattern, a repeating pattern on/off, or can you determine that something is modulating the interference?
A AM radio or cheap telephone may give you insight to the problem, but again, maybe not. Here is some generalizations that is guaranteed to get me in trouble for posting:
IF the interference IS or IS NOT detectable by a cheap phone, or AM radio, turn on the TV (not cable) to Channel 5 and then Channel 2. IF the same is visible on both 5 and 2 (sometimes CH 5 or 2 may be stronger), THEN it is a good chance it is CB radio. Transmissions will be intermittent in nature, and if you can detect it with a cheap phone or AM radio, you will hear the audio transmitted. 10-4 Good Buddy!
IF the interference is rapid in ON/OFF sequence (1/4 second pulses or 6-8 second bursts), followed by pauses of 1 to 3 minutes, AND there is no apparent modulation, THEN it is a good chance it is a paging system, or MORSE CODE, and origin is from a local ham, of paging company. Find by looking for antennas. Approach them without an attitude, and you'll get far.
IF the interference is random, with no modulation visible or audible in the interference, it could be many things, pagers, ham transmissions.
Take your time, be polite, and good luck.
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by Jan Janowski edited by Flippant
last modified: 2007-09-24 08:23:12