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In article .com,
Paladin wrote: Recently....NO MATTER where I position the mag. on the cover, I GET a small signal that "CAN'T" be squalched away !!! It's just white noise/static !!! IF I move my handie-talike to around the same area(with-in 10-12 ft.) IT ALSO reacts the same way !! WHAT COULD BE causing this PHENOM ??? I've seen 2-meter spectrum noise from: - Cable-TV leakage - worst is around 145.250, apparently due to the video carrier leakage on Cable Channel 18. - Multiple spurs generated by a switching power-supply regulator in a Netgear wireless access point / IP router. The spurs were apparently being radiated directly from the PC board, out through the case - the power supply lead was adequately choked but this didn't stop direct radiation. Other models of router (including one from the same manufacturer) did not exhibit the problem. - Noise radiated from telephone lines which have DSL networking service enabled. Although the DSL signal is supposed to fall entirely within the HF range, I believe that it has significant harmonics up into the VHF which are not filtered out by the DSL modems. - Harmonic noise generated by a defective oscillator in an Ethernet hub. This one was a doozie - it drifted through the 2-meter band as temperature changed, and it caused horrendous squelch-tail buzzing on several repeaters miles away when it drifted through their input frequencies. Apparently it was radiating out through the owner's Ethernet cables, and also getting back into the building wiring through the power cord. A device doesn't have to be complex to cause VHF QRM! Although it didn't actually cause QRM, I did find another source of possible interference recently when I tested and repaired a little two-tone audio oscillator another ham had given me. It was a simple battery-powered two-transistor oscillator based on a 1970s article in QST. Due to its design (two simple twin-T oscillators using 2N2222 transistors) it was prone to break into a parasitic oscillation at one point in the audio curve... it was putting out a nice 1 kHz audio sinewave, with a VHF parasitic around 20 dB lower in amplitude, wandering around from 130 to 160 MHz. One ferrite bead on the base lead of each of the two transistors completely cured the problem. Other people have reported nasty-noisy signals from oscillations in TV-antenna preamplifiers... these have caused interference to 2-meter ham operators, aviation band, and even to GPS (see the page at http://www.gpsworld.com/gpsworld/art...l.jsp?id=43404 for a summary). Can't figure this one out.....any ideas what to do ??? please... Do the "turn off and unplug" bit again, but go even further. For starters, try turning off the main breaker for your whole house/apartment. This will be a very clear way of telling you whether the noise source is internal or external. If it's internal to your home, turn the breaker back on and then start unplugging every single device in the house (no matter how apparently harmless) one at a time until the QRM goes away. If it's external, go hunting. Get yourself a 2-meter directional beam antenna (or make one - Google for "tape measure Yagi") and start DF'ing. If you track it to a neighbor's house, introduce yourself politely and explain the problem and try to enlist their cooperation in finding the source of the emission. See if you can find someone in your area who has an RF spectrum analyzer good up to 150 MHz or so. It can be very instructive to look at the whole 2-meter band, and see whether you're seeing a single carrier, broadband noise, or multiple narrowband spurs. A spectrum analyzer, hooked to a portable Yagi via a 20' coax, makes a *very* nice "characterize and locate" tool. When I helped my city's RACES EC locate the source of some nasty 2-meter RFI which was desquelching his radios and interfering with his ability to receive simplex, it took about 10 minutes with an analyzer-and-Yagi combination for me to be able to say "Well, it's your next-door neighbor's condo, upstairs, in the back, polarized at around 45 degrees from the vertical. and is multiple spurs at about 50 kHz separation." The bad news is that on many 2-meter frequencies, there's so much hash and garbage in urban areas that it's necessary in practice to turn on a receiver's tone-squelch, and force the receiver to remain muted until it hear's a repeaters output CTCSS tone. If your repeater doesn't put tone on its output, then this won't work, alas. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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