Difference between analog and digital cable signal

November 19, 2005 12:44 PM

My father-in-law just bought a *nice* big TV... That doesn't have anything to do with the question, though. He got an HDTV box and all the digital channels and the HDTV channels come through fine but the analog channels are very snowy. I would expect that the digital channels would pixilate if the coax going into the box is bad. Could this be a splitter/crummy wiring problem? I don't know how the digital channels make it through while the analog channels have horrible quality (some to the point of the TV throwing up a blank screen because of the "snow" effect.
posted by ajpresto to technology (8 comments total)

Analog quality can worsen if the signal's traveling over a longish length of cable. But I wouldn't expect it to be as bad as you describe. If you plug the cable directly into the TV, bypassing the cable box, is the result the same? If not, probably a wonky cable box. If so...?
posted by schoolgirl report at 2:02 PM on November 19, 2005

I ran into the same problem last week when I cabled for a set in a room that didn't have one before. In the process I had to split an existing cable. I ended up with one set that was terrible in the analog range but digital was ok..

Turned out to be a bad cable end I had installed where I had to do the split... A new end fixed the problem...

Worth checking and an easy repair....
posted by HuronBob at 2:04 PM on November 19, 2005

So there is the potential for crummy cable.. interesting.

Yeah, if you take the box away, the signal is still just as bad. I guess we'll take a look at the cable ends and the splitter back in the wall.

Thanks!
posted by ajpresto at 2:06 PM on November 19, 2005

I've found switching from cheaper rg59 coaxial cable to rg6 "quad shield" cable to reduce snow considerably. I had always thought cable was cable and the more expensive crap was just a way to rip off idiots, but at least for TV, it's worth spending the extra $5~.
posted by stavrogin at 4:38 PM on November 19, 2005

I'm not certain what's in the wall right now. Probably the cheap stuff. But again, I'm confused about why analog looks like crap while the digital comes through okay. My experience has been that digital is more sensitive to bad connections, etc... I've had what I thought to be pristine analog pictures and pixelating digital. This seems counterintuitive to me.
posted by ajpresto at 4:43 PM on November 19, 2005

You've just seen why digital communications generally works better than analog, and so why everything is trending towards digital: given a crappy transmissions channel, a digital signal may get through completely perfectly whereas the analog will look like ass. See also "cliff effect", "spread spectrum", 8VSB vs CoFDM, Viterbi, Reed-Solomon, etc.

As to your specific problem, it could just be interference in the lower frequencies where the analog channels are. But also try swapping out splitters, and also try an attenuator -- could be too much signal.
posted by intermod at 5:50 PM on November 19, 2005

i'm curious as to why you're running RF to the display in the first place.

Ideally, you should be sending the video signal to the TV using HDMI, Component, S , or Composite video, in that order. Using the monitor inputs separates the audio and video and bypasses the set's tuner, which is why you have that plethora of inputs on the back of that fancy new HDTV.

As for RF, rg6 is preferable to rg59 and yes, cable construction and termination do impact signal quality, anywhere in a signal path.
posted by PareidoliaticBoy at 6:19 AM on November 20, 2005

I'm sorry I wasn't clearer. I was talking about the input from the wall to the cable box. I have a multitude of connections running from the box to the TV, none of which are Coax/RF. Although, I was looking for a list exactly like yours, prioritizing the connections from the box to the TV. We went to Radio Shack to buy cables and found that HDMI were like $120. I'm glad we didn't buy it from there because you can get them at good quality for about $50. Poor quality at $20 on eBay.

Anyway, the multiple connections from the box to the TV were to check on the signal loss... was it going to the box or coming out of the box? Since the signal sucked across Component and S-video connections, the hypothesis is the input from the wall is poor.

I have to get back over there and play with the coax. Thanks!
posted by ajpresto at 7:51 AM on November 20, 2005