Problem with snow on certain channels

Okay, I'm probably the last person on Earth who doesn't have cable t.v.

I found that by getting one of these WalMart antennas with the multi-position knob and running it through a signal booster along with a

50-ft length of coax cable taped in a fairly tight loop, I can get very good reception on several channels. That booster works great. Even the PBS station that doesn't come in that well without it looks fine with it. I have the antenna signal run into a VCR via the coax in and going out to the tv via the stereo RCA connections for sound and the composite video out.

However, there is one channel, the CBS affiliate in the area, that while I can get the picture to be generally sharp, there are these horizontal bands of snow that crawl up from the bottom. As one gets about 2/3 up, another starts. They're also accompanied by static in the sound. I've tried numerous positions, even tried taking the rabbit ears outside, even on the roof. No matter how clear the picture is otherwise, those horizontal bands and static won't go away. I tried turning off everything else in the house to see if something was causing it, to no avail. Tried going directly in from the antenna to the coax connector on the back of the t.v. to see if it made a difference, no difference. It only became an issue for the first time when there was something on that I wanted to tape the other day.

Looking for insight as to what causes this and what can be done to eliminate it? (Besides getting cable/satellite etc.)

Thanks in advance for all input. I don't have a background in electronics/broadcast etc. but don't hesitate to get technical. I can always do research to bone up.

Those bands are usually caused by electrical arcing. That's an external source of interference - it's not happening because the CBS signal is weak, it's happening because something else is generating a signal on the same frequency. The interference source is much closer than the CBS station, so you probably won't be able to get rid of it by moving the rabbit ears.

I wonder if AM radio reception is also unusually noisy? You may need to call your local electric utility and ask them to check for "leaky insulators" on the power lines.

What city are you in? (that way we can judge how far you are from the TV transmitters and what channels the stations are on. That has a bearing on how to fix the problem.)

Wild guess: the CBS affiliate is the lowest channel and the only one below channel 7?

--
Doug Smith W9WI
Pleasant View (Nashville), TN  EM66
http://www.w9wi.com

good reading on

see eliminating ghosts, bottom of page

martin

Serious error. All shortcuts have disappeared. Screen. Mind. Both are blank.

The horizontal bands of snow are more than likely casued by some kind of arcing of the 60 Hz line. The TV vertical sync frequency is 59.94 Hz; so, the 60 Hz related noise slowly moves relative to it. You might be able to locate the noise source by walking around with a portable AM radio, tuned to a vacant channel. Check out the power line on the street, and neighbors houses.

Fish tanks are notorious for causing this type of noise. Also, old oil burners.

Tam/WB2TT

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That is likely being caused by RF radiation from the AC power lines. Today's TV's have great filtering, but years ago, ac hum leakage would cause what we called "hum bars" that moved up the screen, exactly as you describe. I'll bet that the TV station with the problem is Low VHF -- that is, one of the channels

2 through 6, as most such radiated interference drops off at the higher channel frequencies. You may have an arcing insulator on a power line, a bad transformer or some item in a neighbor's house. Most power supply circuits in electronic equipment draw current only on the voltage peaks, so the switching-on of diodes and regulators will reflect little spikes back into the power line at 120 Hz, just a hair over twice the TV field rate, so you get two per screen and they move up because of that hair's difference.

Three easy things to try: Install an AC line filter; a surge/spike suppressor is NOT the same thing. Ground the TV's chassis if the TV has only a 2-prong plug. (This used to be verboten in the bad old days of hot-chassis sets -- no more.) Try taking your long-cable rabbit ears away from the set on a

*horizontal* line -- that is, away from the house, just not *up*, since there are wires in the attic that could be radiating power line hash.

Final point: In spite of your best efforts, maybe you didn't turn off enough in the house. The furnace power supply, garage door opener, appliances with digital clocks in them -- all these and more have electronic power supplies that draw current only on the peaks. A dimmer in your neighbor's house could be the culprit. Some computer power supplies are real stinkers. Welcome to my nightmare!

"Sal" (a former EMI engineer)

PS: You're going to love digital when you make the jump. Doug is right.

Actually, the NBC affiliate is the clearest channel on 2. CBS is 6, ABC is

9, WB is 18, PBS 24, Fox 35.

I'm in Deltona, which is south of Daytona Beach.

Well, I was way off: I was guessing you were in Charlotte...

If you're in Deltona, you're *really close* to the channel 2 tower. (a mile southwest of Orange City) Channel 6 is somewhat further south, near Bithlo. Channels 6 and 9 are actually on the *same* tower - but the higher frequency makes channel 9 much less susceptible to this kind of interference. Anyway, that explains why you have problems with channel 6...

Tam and Sal's suggestions are well-taken. (well, I suppose you probably don't have oil furnaces in Florida) Indeed, one co-worker once had a TV that interfered with itself! -- a RF filter on the power cord fixed that problem.

The suggestion to try a digital box is also a good one. $198 at Wal-Mart, stores like Circuit City also carry them though I don't know if you can get one quite that cheap elsewhere. Connects to your existing TV **IF** it has direct audio and video inputs. (if not, I think you can buy an adaptor -- a "RF modulator" -- at Radio Shack for less than $50) You'll get an absolutely *beautiful* picture - none of the seasonal interference that I'll bet plagues channel 6 in late spring and early summer - and there's a good chance you'll get a few extra channels that aren't available with analog TV. There's no monthly fee, once you've bought the box that's it.

--
Doug Smith W9WI
Pleasant View (Nashville), TN  EM66
http://www.w9wi.com

I was an engineer at Ch 55 in Orlando in 1988 and Ch 6 always had a poor picture. Their signal was weak and there was a lot of noise in their chroma. I ran into their chief engineer at one ot the local parts houses one day and he was complaining about how bad NTSC was and that he couldn't wait to go digital. It was all I could do to keep from laughing in his face. The low budget Christian station (Ch 55) was running the old RCA TK46 cameras and had the cleanest live video of any station in the market. The entire engineering staff was two men to maintain four sites and our annual budget for the station was less that one tenth of what they spent. WE had a mix of very old equipment and state of the art but it all worked when we needed it. BTW, the Ch 55 tower is across the highway from Ch 2 in Orange city. Its 1749 feet and Ch 2 is around

1200 feet. The last time ai was at the CH 55 tower five of the Orlando FM stations were on a single antenna array at about 1000 feet. The transmitter site was the cleanest layout and building I've ever worked in, in the broadcast industry.

--
Beware of those who suffer from delusions of adequacy!

Michael A. Terrell
Central Florida

What you described is usually caused by a local interference. This can be from a communications system that is emitting some harmonics that are near to the same frequency as the station you are trying to receive. It is also possible that there are two TV stations that are far apart, and you are about half way between, and they are on the same channel, or very close to each other's channels, or one is generating a harmonic to the other.

Your best way to have proper reception, is to have a cable or satellite service. Using terrestrial service to have TV is not practical these days, unless the station is local to you. Your viewing of what is out there is very limited. Many of the TV stations are looking at dropping terrestrial service. This is very expensive to keep up, and it is very limited.

--

Jerry G. =====

I found that by getting one of these WalMart antennas with the multi-position knob and running it through a signal booster along with a

50-ft length of coax cable taped in a fairly tight loop, I can get very good reception on several channels. That booster works great. Even the PBS station that doesn't come in that well without it looks fine with it. I have the antenna signal run into a VCR via the coax in and going out to the tv via the stereo RCA connections for sound and the composite video out.

However, there is one channel, the CBS affiliate in the area, that while I can get the picture to be generally sharp, there are these horizontal bands of snow that crawl up from the bottom. As one gets about 2/3 up, another starts. They're also accompanied by static in the sound. I've tried numerous positions, even tried taking the rabbit ears outside, even on the roof. No matter how clear the picture is otherwise, those horizontal bands and static won't go away. I tried turning off everything else in the house to see if something was causing it, to no avail. Tried going directly in from the antenna to the coax connector on the back of the t.v. to see if it made a difference, no difference. It only became an issue for the first time when there was something on that I wanted to tape the other day.

Looking for insight as to what causes this and what can be done to eliminate it? (Besides getting cable/satellite etc.)

Thanks in advance for all input. I don't have a background in electronics/broadcast etc. but don't hesitate to get technical. I can always do research to bone up.

The OP does have a full complement of stations local to him. If he were in, say, North Dakota he might feel differently.

Terrestrial service is impractical only if price is no object. What's cable these days, $30/month? (I suspect quite a bit more. I hear of plenty of people paying more than $100/month after premium channels.) That's *at least* $360/year, probably quite a bit more.

You can buy a pretty nice antenna and a digital STB for $360, and they'll last more than a year. (+/- hurricanes.....)

If you have to have those extra channels like HBO, Fox News, ESPN then I guess you need cable/satellite. There *are* those of us who don't find the extra channels worth the cost.

I would not count on terrestrial transmission going away in the near future. A number of rather large firms have rather large investments in local TV stations, and will not surrender those investments without a fight. Terrestrial transmission continues to be the easiest way to get those local stations' programming to outlying cable systems.

--
Doug Smith W9WI
Pleasant View (Nashville), TN  EM66
http://www.w9wi.com

I'm sorry, Jerry, but for US analog TV, this is almost 100% incorrect:

Harmonics do not appear as a pair of horizontal lines slowly moving up the screen

Two (or more) stations on the same channel may produce a closely spaced pattern of hundreds of horizontal lines (co-channel interference), not two lines.

Closely spaced channels do not interfere harmonically; harmonics are MULTIPLES.

Terrestrial TV is quite practical and getting more so every day. Perfect digital pictures from 50+ miles are an everyday reality for many of us.

Cable and satellite are superior to OTA (broadcast) only in raw numbers and maybe an immunity to certain forms of interference.

Terrestrial service is increasing to meet a constantly growing demand.