Why are only some of my cable channels static-y?

February 7, 2006 7:36 PM

Why are some of my cable channels covered in snow, while others are perfectly fine?

A select few of my cable channels, namely channels 2 through 6 (the local network channels), are so covered in snow that I can barely see the picture. However, the rest of my 60-odd cable channels come in clear. I just noticed tonight that if I watch channels 2-6 through the VCR, the snow is gone. What gives?

My TV set-up is as follows:

wall jack -> 50' coax cable -> VCR/DVD player -> 2' push-on coax cable -> TV jack.

posted by geeky to technology (17 comments total)

call your cable company and have them come out and test. most likely they need to add a booster on the pole outside. you probably are having a low signal in the frequency for those channels, and when you split it, you are losing enough of the signal to get snow.

also, make damn sure your cables are connected snugly. i had that problem once.
posted by kneelconqueso at 7:41 PM on February 7, 2006

Sounds like the TV/Video button, which toggles control of the cable input on your TV between the VCR and the cable provider.

You'll see more interference in the lower channels even when everything is set up correctly, I think. When my signal is bad I'll see a lot more noise on 2-5 (sometimes 2-7), and then again on 14-16. I'm not sure why exactly...
posted by Chuckles at 7:47 PM on February 7, 2006

Same thing happened to me before the switch to digital. I never figured it out, but doing away with the VCR/DVD helped.
posted by geoff. at 7:56 PM on February 7, 2006

kneelconqueso - I'm really trying to avoid calling my cable company, as their customer service sucks, to put it lightly. I've called about this before, and they usually just blow me off. Besides, I figure if the picture is clear at least from the wall to the VCR/DVD player, then the problem isn't on their end. Checked the cables, all connections snug.

Chuckles - It's not the tv/vcr button. If I watch TV with the VCR completely off, the picture is snowy. If I watch TV with the VCR on set to TV, the picture is clear.
posted by geeky at 8:06 PM on February 7, 2006

This might sound really dumb, but make sure all the cables are screwed in tight. Something similar was happening with our TV, but on the top end channels, and fiddling with the cable fixed it.
posted by jennyb at 8:08 PM on February 7, 2006

Sorry if the TV/VCR thing was too basic :P

The first thing I should have thought of is: test it! Connect the cable straight to the TV and see how it performs. It will probably be fine, which means it is the VCR and/or the short piece of push on cable.

It does sound like a week signal problem. Two possibilities...

The VCR may be doing nasty things to the signal. If you have video-in on your TV, try a cable splitter. Feed signal to the VCR separately from the TV. Of course the splitter will weaken the signal a little on its own, you will have to experiment a little to see what helps.

The cable between the VCR and the TV may be bad, or not connected properly.

In answer to my questions above, here is the list of North American Cable Television Frequencies. You would expect noise to affect lower frequencies first, turns out 14-22 are actually lower frequency than 7-13. I have a feeling there may be another island of noisiness in the high 20's. Noise effects lower frequencies first because... Well, it has something to do with the shape of background electromagnetic noise, I expect... Hmm...

posted by Chuckles at 8:24 PM on February 7, 2006

Oh oh, didn't close my blockquote... Oops!
posted by Chuckles at 8:25 PM on February 7, 2006

It may be that the VCR's own internal channel (the one it uses to send stuff to the TV) is swamping the cable signals. Try switching off the VCR and temporarily hooking your 50' cable direct to the TV. If all channels clear up, that's most likely the problem.

The fast workaround, as you've already found, is to let the VCR receive the cable signals for you and relay them to the TV on its own channel. Which kind of sucks if you want to be recording on the VCR while watching something else on one of those channels.

If your VCR has video-out and audio-out connectors, and your TV has video-in and audio-in, there's a proper fix. Just wire those together with the appropriate cables, then feed both VCR and TV from the cable via a splitter box instead of going cable->VCR->TV.

On preview: if things are bad when the VCR is turned off, it means that there's some turned-off VCR circuitry connected to the signal path, and the high-channel signals just happen to be less affected by this than the low-channel ones. The fix, as before, is to remove the VCR from the RF signal path between the cable outlet and the TV.
posted by flabdablet at 8:41 PM on February 7, 2006

It's the push-on cable. When you watch through the TV, it's tuning the signal coming all the way from the wall, and that signal is getting trashed by that crappy cable. When you watch through the VCR, it tunes in the good signal from your 50' run, then basically regenerates it and sends it out to the TV. The VCR's regenerated signal is strong enough to overcome the loss in your bad cable.

I'd replace the push-on cable with RG6 , and the 50' with a proper length of RG6 (if it isn't already). RG6 is a newer, higher-grade cable, which replaces the old RG59.

Incidentally, when I worked for a TV co, "replace all push-on cables" was a troubleshooting step even before starting to work on the actual symptoms. If they weren't actively causing problems, they would be soon.
posted by pocams at 8:41 PM on February 7, 2006

Sorry, I didn't answer the 2-6 question. Channels 2 through 6 are in a totally different frequency range (54 - 88 MHz) than 7+ (174 MHz and up) are. (Historical reasons.) That means that interference in the lower frequencies -- for some definitions of "lower" -- will hit 2-6 and not the rest.
posted by pocams at 8:56 PM on February 7, 2006

Push-on cables are fine for this application, but the ground tabs loosen easily, so you might have to tighten it up a bit. Just use a pair of pliers to make the outside diameter a little smaller, but be very gentle about it.

Regarding the noise issue (yes, I know I'm the only one interested in this :P). Here is the background electromagnetic noise spectrum. You can see how fast the background noise is falling as you move up in frequency within the cable band. I still think something is missing from the picture... It is stuff I should know, but it has nothing to do with the question, maybe I should stop :P
posted by Chuckles at 9:02 PM on February 7, 2006

Guys, doesn't anyone here know how a cable company works?

Temporary outages of one or a few channels is almost always a satellite feed gone bad at the cableco's local office.

I don't know if you've ever seen a cableco office, but they always have about 20 huge dishes out back.
it
This is why when the cable folks come around saying that they're better than the sat services, it's really just a bunch of crap. They're delivering content to you that comes straight off of their sats, and just delivering via a different medium.

Usually, they've either got engineers watching the feeds, or customers complain and then they work out whatever's gone wrong with the dish that receives that particular set of channels.

Dead bird on the dish, wind moved the dish, transponder out on the actual satellite, a zapped LNB, can all knock out a sat feed.

If you did nothing and the channels just came back on their own, your equipment is fine.
posted by SlyBevel at 10:03 PM on February 7, 2006

Geeky: It's not the tv/vcr button. If I watch TV with the VCR completely off, the picture is snowy. If I watch TV with the VCR on set to TV, the picture is clear.

You've identified the problem. The VCR's switching is active. The TV setting means "pass everything straight to the TV without sending it through the VCR tuner." The VCR setting means, "Everything goes through the tuner first, then through the whole play-viceo-dealie stuff, then to the TV." Neither work in your VCR without power, and this is somewhat common in my experience.

A few options:

a) Leave the VCR powered up and on TV when you want to watch TV (this is the purpose of the TV/VCR button!).

b) Leave your TV on channel 3 or 4 (whatever's selected on the back of the VCR), and change channels with the VCR.

c) Get a manual switch with multiple inputs and a single output. Hook the cable into one input, the VCR into a nother. Click the buttons when you want to go from VCR to TV.

d) With a cable box, hook it up between the wall and VCR. I have mine wall->satellite box->VCR/DVD (always on and on TV)->TV.
posted by dsword at 11:40 PM on February 7, 2006

I have to second what pocams said. Low-end freq. loss from the RG59 is your problem. Used to happen to me until I rewired my house. Buy some bulk cable and connectors and teach yourself how to crimp RG6. ;-)
posted by rhymesinister at 2:12 AM on February 8, 2006

Thanks everyone!

I thought about just leaving the VCR on all the time and watching TV through it, but I noticed that the VCR only picks up about 15 channels (out of 60), like it only gets basic cable. Odd, since the cable line from the wall goes directly to it.

I will get some new cables on the way home from work today and try that. I'll also tinker around with just skipping the VCR, going wall jack -> TV and using a cable splitter.

I will let you know what works or what doesn't!
posted by geeky at 5:53 AM on February 8, 2006

SlyBevel:
Guys, doesn't anyone here know how a cable company works?

You're awfully snarky for someone who's thoroughly mistaken. Satellite signal problems will affect a group of channels, but not usually a block of channels. For example, it might hit 15, 23, 27, 42, 43, 44, and 48, because those are all on the same feed. A contiguous block of channels probably has channels from a variety of satellites, and 2-6 probably have some locals that aren't from satellite at all.

Secondly - this isn't an outage, it's a snowy picture. The vast majority of satellite signal is digital, so signal problems in that path (including all your examples) would cause digital tiling and breakup, not snow. The snow is a dead giveaway of a problem between the cable headend and the customer.

As an aside, the cable guys are saying they're better because they have bigger dishes and more amplification, so rain/snow/fog/etc. will knock out a little DirecTV dish well before it touches their big 8' or 10' ones.

Sorry for the OT-ness - best of luck with the problem, geeky.
posted by pocams at 3:16 PM on February 8, 2006

I feel kinda dumb now, but after twisting the coax cables connected to the VCR a bit, the snow cleared right up! No new cables needed. And all this time I thought my cable just sucked... doh!

Thanks again for all the suggestions. When I get some extra cash, I'll replace those coax cables anyway. It's kinda silly to be using a 50' cable when the TV is right next to the jack, but it's just what I happened to have around.
posted by geeky at 4:48 PM on February 8, 2006