Wikipedia:Reference desk/Archives/Science/2020 May 15

= May 15 =

RF constant transmission
I have a TV antenna in my attic. I moved it and lost all but 2 channels. I moved it back to where it was and got all the local channels back. I then noticed that when I stand where the antenna didn't work, my cell phone loses almost all reception. I also don't pick up my wifi. I experimented and found that the "dead zone" is a line from one side of the attic to the other. I went outside and climbed up a ladder and found the line extended outside the house. I though it might be a signal flooding everything, so I got a small radio to see if I could hear anything. Without turning it on, the two speakers began chirping and clicking at high speed. Now, I'm wondering, what RF signal in rural South Carolina travels in a tight beam with enough energy to excite speakers in a radio that isn't turned on and, as a result, blocks television and cell phone reception? The only hint I have is that there is a fire station in the general direction of the line in one direction - nothing but farm land in the other direction for miles. Past the fire station, a good 20 miles away, is an airport. 97.82.165.112 (talk) 12:12, 15 May 2020 (UTC)
 * A simple experiment is to turn off the main breaker for your home to see if the phenomenon stops. That would pretty much tell you if it's coming from inside your home or not (although a few possible sources have battery backups). 13:04, 15 May 2020‎ Jc3s5h
 * Another possibility is that it is some kind of local "node" for some signal much farther away. Wave phenomena like radio can have strange behaviors where a signal can have localized areas of high and low signal strength due to the oddities of harmonics and wave interference.  You can find this with sounds too; especially in rooms with complex shapes you will occasionally find locations in the room where there are sound "dead spots" and other locations with strange audio phenomena like unusually loud sounds and weird flanging effects and things like that.  I suspect that radio signals can produce such spots as well, and perhaps you just happen to have one in your attic.-- Jayron 32 14:23, 15 May 2020 (UTC)
 * This sounds like it is electromagnetic interference. Perhaps it is coming from a wire in your house. Some power supplies, and electric motors can put out a strong unwanted signal in radio waves that interfere with reception. Even fluorescent lights put out a weak broadband interference. Electronic devices are often more narrow band emitters, just interfering with some radio stations but not others. Graeme Bartlett (talk) 23:34, 15 May 2020 (UTC)
 * Indeed, I believe that's what Jc3s5h's suggestion was about testing for. --76.71.5.208 (talk) 01:18, 16 May 2020 (UTC)
 * I think I found it. Cutting all power in my house didn't help. I can't check TV, but my phone gets almost no signal and my radio keeps ticking, even if it isn't turned on at all. It is a very narrow dead zone, about 5 feet wide. When my radio is on, I still hear tick sounds, but I can tune into a station. It gets much louder if I move out of the dead zone. Using an antenna on a long stick and my radio, I traced the line of the dead zone to the back of my property to the front, about 500 yards. That gave me a very good line. I followed the line on the map and marked locations where it crossed a road. I followed that and I found that the line crosses a large antenna tower, marked as private property for the airport. There is a wide flat thing sticking out one side. If I get my antenna up near it, I can hear the same clicking on my radio. Going to the other side of the antenns structure, I get no interference. Tracing the line the opposite direction on the map, it crosses the airport. So, I googled pictures and it appears this is one of the outer-middle-inner towers. I'm not sure what they do, other than create a narrow line where I can't pick up radio signals very well. I'm not overly concerned, just curious. I moved my TV antenna far away from the dead line and I am getting far more broadcast channels than I ever got before. 97.82.165.112 (talk) 14:37, 16 May 2020 (UTC)
 * Do any of the signal audios in the Marker beacon article match the pattern of the clicks? Also, if you draw a line on a map from your house to that marker beacon, does it cross the approach line to the runway at a right angle? The distance between the close end of the runway and the beacon should be about 1.85 km for the outer, and roughly 1 km for the middle marker. --Lambiam 17:36, 16 May 2020 (UTC)
 * The clicks sound random to me. I checked the map. In my mind, it is many miles between the tower and the airport because there is no direct road and it takes a good 30 minutes to drive between them. But, according to Google Maps, they are about five miles apart, if I'm reading it right. You can check. GSP is an easy airport to find on Google Maps. Southeast, you will find Sugar Tit. I live very close to that. The tower is next to the power company at 417 and Bens Creek Rd. On the map, it is just a field, so it must have been built between the map photo and now. 97.82.165.112 (talk) 12:15, 17 May 2020 (UTC)
 * Hmm. So the tower is really quite far from the approach flight path, which would pass over the Walmart on Woodruff Road. But a line perpendicular to the approach flight path going through the Laurens Electric site does cross that path at about 1.5 to 2 km from the end of the runway, which is consistent with an outer marker. Wikipedia states that Sugar Tit is located around the junction of State 101 and State 296. The position on the perpendicular line closest to that junction is near to 34°49'52"N 82°09'50"W. The line crosses Brockman Rd near what (at least according to Google Maps) is 760 Brockman Rd. --Lambiam 11:09, 18 May 2020 (UTC)
 * I went to the power company and asked about it. No secret. It is a direct-line radio communication line to the BMW factory. They kept cranking up the power because they were getting interference. I explained that the interference was probaby my attic because my house is on the highest hill in the area and my attic is well above the tree tops. The guy I was talking to didn't think one house could cause that much interference, but he said the people who isntalled it said it was well above everything in the area, so they will look into it and see about moving it so they can communicate without the interference. One mystery solved. 97.82.165.112 (talk) 19:24, 18 May 2020 (UTC)