I think I found the source of RFI in my apartment

[wa2ise]

For the past year or more, a persistent intermittent (half second brittz every few tens of seconds) burst of RFI that would pollute the MW AM band was happening. Took a while to track down. Thought maybe a bad thermostat in the electric water heater, turn its breaker off, not it, still hear it. Try other breakers, seems one breaker cycling makes it go away for about 20 minutes. I eventually find that it's the power supply charger for my laptop. Seems when the laptop blanks its screen (screensaver and powersaver mode) it makes the RFI noise. Tickling the laptop mouse makes the screen light up and the RFI goes away. Or if I unplug either end of the power supply (120V side or the 19VDC output side). Okay, need to filter the power supply charger. I have a couple of those Cornell Doublieer powerline RFI filters (small metal box with 3 prong power plug and socket and RFI filter inside, and that looks to quiet the RFI down to almost nothing.

And for the longest time I figured it was faulty electrical wiring in the apartment building. I could see the lights flicker ever so slightly when the RFI bursts happened. That power supply must have been sucking down much amperage for brief periods of time. The filter is rated for 3 amps, but that's continuous. So I don't think it will get blown out...

[Jeffhs]

I have an RFI problem in my apartment as well, only I don't think I'll be able to do much about it. The problem is harmonics of 15,750 Hz, the horizontal oscillator frequency in TVs. They appear at random spots on the AM radio dial and almost always seem to show up right on top of weak music stations I'd like to listen to; there are several such stations within 50-80 miles of here that are completely unlistenable due to the interference. Unlike wa2ise's laptop charger which he can shut off, however, I think I am more or less stuck with my interference problem, as there are several tenants in my building who apparently like watching soap operas or those crazy talk shows on TV in the afternoons.

The interesting (and baffling) thing about my interference problem is that it doesn't seem to show up much, or at all, after dark. That's TV prime time; I'd think I would have even more of an RFI problem on the AM radio dial then than I would in the daytime. I think, however, that the reason I don't have nearly the problem with horizontal oscillator birdies on my AM radios at night is there are more 50kW stations coming in after dark, and even smaller stations may be running more power (in the thousands of watts) at night than they run during daylight hours. I don't know of any stations in or near my area that do this (most smaller stations in the Great Lakes region that do not operate at 50kW actually run less power with directional signal patterns or sign off after dark), but I have seen listings (in RadioStationWorld.com) for stations in the southwestern US, particularly in border states such as California, Arizona, Texas, etc. that in fact do increase, rather than decrease, their power output after sunset local time. I think they do this to combat interference from stations in Mexico. I'm amazed that stations in my area (which is only a mile or so from the south shore of Lake Erie) or those in northeastern US states like Vermont, Maine, Massachusetts, etc. do not do this, as they are not that far from Canada. I'm only perhaps 150 miles from Detroit, which is a hop skip and a jump across the lake from Windsor, Ontario. The latter has AM 800 (CKLW), which runs 50kW 24/7 (no nighttime power decrease or signal pattern changes that I know of) and has for decades; no interference problems. The same goes for the 50kW stations in Detroit, which are heard in southwestern Ontario as well. This is amazing, to me, especially on 800 kHz, since the US stations on that frequency used to have to sign off at sunset local time to protect CKLW from interference. In those days, before the FCC did away with clear channels, CKLW was the only station on 800 kHz at night in North America, and at most only two stations could operate after dark on the clear channels in the US. In my area, the dominant station was WKYC 1100 (now WTAM) and, on the West Coast, KFAX 1100 in Los Angeles. The other stations, mostly daytimers, had to sign off at sundown local time. The other 50kW station in my area, WGAR 1220 (now WHKW) was not a clear channel operation. It had to, then as now, decrease its power and change its signal pattern at night to protect a station in southwestern Ontario on the same frequency. A 50kW sportstalk station on 850kHz in Cleveland must decrease power to 4.7kW (4700 watts) with a different pattern at night for roughly the same reasons, the only difference being that the stations being protected from skywave interference are in Denver and Boston. Both these stations are 50kW as well, but if the Cleveland station ran its 50kW signal (same antenna pattern) all night it would clobber the other two, but good -- even, I think, during so-so propagation conditions. About 25 years ago, I heard KOA 850 in Denver early one Monday morning (about 1 a.m. or so, IIRC), after Cleveland's station on that frequency (WRMR, IIRC) had signed off for technical maintenance -- the first time I had ever heard any AM radio stations west of the Rockies from northeastern Ohio. I haven't heard anything from Colorado, or anywhere else further west than Texas, on AM since. Probably due to that 15750 Hz TV horizontal oscillator interference I mentioned above.

[jr_tech]

"AM 800 (CKLW), which runs 50kW 24/7 (no nighttime power decrease or signal pattern changes that I know of) "

CKLW runs a considerably different pattern at night, according to the FCC:

http://www.fcc.gov/fcc-bin/amq?list=0&facid=98868

jr

[Chad Hauris]

One time I had incredibly strong RF interference on AM and shortwave and I never found what the source of it was. I turned off the main breaker to the house and used a battery powered AM radio and it was still there. Luckily it ended up going away...maybe it was an insulator on a power pole arcing or something? It blocked out almost all AM reception with a loud buzzing sound.

[AUdubon5425]

Denver is east of the Rockies, which is why we can pick it up. KOA is the furthest station west I can regularly get. Up your way, I regularly pull in WTAM, KDKA, and WJR.

[AndyMack]

Originally Posted by Jeffhs

The other 50kW station in my area, WGAR 1220 (now WHKW) was not a clear channel operation. It had to, then as now, decrease its power and change its signal pattern at night to protect a station in southwestern Ontario on the same frequency. A 50kW sportstalk station on 850kHz in Cleveland must decrease power to 4.7kW (4700 watts) with a different pattern at night for roughly the same reasons, the only difference being that the stations being protected from skywave interference are in Denver and Boston.

1220 is a Mexican Clear channel, but since Cleveland is far enough away from the border, they are allowed to operate 50kw DA-1, meaning they run the same pattern & power both day & night. Used to listen to then-WGAR back in the late 70's here in eastern NY with relative ease since there were no other signals on the channel back then. Can still hear WHKW, but there's one or two other signals on 1220 at night now.

KOA Denver was the Class 1-A station on 850 until Boston was shoehorned in with a directional pattern that puts most of their signal out over the fishes. After Boston came on, rendering KOA a defacto Class 1-B station, other stations were allowed to operate on the channel, including Cleveland and the old CKVL Montreal (long silent now). Ironically, there was a 10kw station in Albany NY on 850 from 1947-1954, WXKW, using a directional pattern away from Denver. KOA was operated by General Electric, which also owned WGY in the Albany area. Since WGY didn't want competition that close to them on the dial (esp. with a great signal like WXKW had), and because KOA had Class 1-A status back then, the folks at GE filed an interference claim against WXKW. That meant that WXKW was never actually fully licensed, but operated under STA status, and having to cut down to exciter power (15w) several times a day to take signal/pattern readings. Because of this and other factors, WXKW went silent in the 50's, and the channel was never reallocated to Albany. The Boston deal was worked out on the corporate end, therefore KOA voluntarily 'gave up' its Clear 1-A status, which then opened the door to allow other stations to fill in the gaps outside their 700 mile protected skywave contour. Boston can run 50kw round the clock, Montreal had to reduce to 35kw at night, and Cleveland down to 4.7kw due to their closer proximity to that contour. Initially, WJW/850 was only running 10kw days, the upgrade to 50kw only happened in the 90's if memory serves me correct, with a good null toward the east to protect Johnstown PA.

[Dude111]

Originally Posted by jr_tech

"AM 800 (CKLW), which runs 50kW 24/7 (no nighttime power decrease or signal pattern changes that I know of) "

I miss CKLW!!

Used to listen to it alot until a local station in my area started running thier IBOC crap 24hrs a day

[bob91343]

My EMI problem is on the 40 and 80 meter bands. Intermittently, especially evenings, I get a surging roar that is somewhat tunable. It's strong, S9 typically, and suddenly will stop. I am sure it's nothing in my own house but beyond that I'm stumped. It surges at about 1 Hz rate and seems to move frequency at random. I have tried to correlate it with the heating system and the refrigerator to no avail. It's gone during daylight hours.

[marty59]

Before it was taken out of operation, there used to be a large ground radar at Selfridge ANG Base north of Mt. Clemens Michigan and you would get a good "blip" everytime time that thing cycled past. Didn't matter if it was a radio, open gain stage on a amp, plugged in Mic etc. that "Blip" would just about penetrate anything. Can't remember when it was shut down, sometime in the eighties after I moved out of the area. And I lived about 10 miles from that thing!

[wa2ise]

Originally Posted by bob91343

My EMI problem is on the 40 and 80 meter bands. ... It's gone during daylight hours.

Streetlight, or some similar light on a neighbor's house that turns on automatically when it gets dark? One that uses an electronic ballast?

[bob91343]

You know, that comment about radar makes sense. I am beginning to think that's what it might be. I live maybe 3 miles from the Van Nuys airport and they might have something there like that. The Air National Guard has closed their operations so that can't be it.

I wonder how I could find out. If I could hear it on 20m I could turn the antenna to see which direction to look.

[jr_tech]

You could use a small SW portable radio and do some "sniffing around" in your house, down the block or to the other side of town if necessary. I usually use something like an Eton E-5:
http://www.universal-radio.com/catal...able/0055.html
You might be surprised to find where the interference is coming from!
jr

[bob91343]

Yeah I was going to do just that tonight but the noise came and went so quickly I never had the chance.

[NowhereMan 1966]

I have an Acer Aspire 3050 and I noticed a lot of RFI when the power supply was plugged in as well.

[bob91343]

I am 100% sure the noise does not originate in my house. It can be late evening, everything switched off, and still the noise persists, with a repetition rate of about 1.25 Hz. It is worst on 80 meters and varies in intensity with peaks at several frequencies. I will try to look at the peak spacing to ascertain more about it.

I now will have to find a portable radio capable of receiving 80 meters. I could strap my TS-440S over my shoulder and schlep a 12V battery but I'd get arrested for impersonating a terrorist.