measure signal strength?

[Eric]

What does it take to measure the Cable TV signal strength at the box? ie: how do you do it, and what are good, bad, and poor values? Thanks Eric

[Eric]

The picture i have is fine, but I have another problem which could possibly be attributed to marginal signal. I have a DVR. Certain channels dont record well, for example, if i record the Science channel programs , then when i play it back there are drop outs and lost audio, picture breakup etc it comes and goes in the recording. Other channels record just fine. Just plain TV watching is good too. I just had this installed by comcast in June and its been a problem since day 1. Do i have a bad DVR? a weak signal? maybe in record mode it requires a slightly higher strength signal? I'm baffled. Eric

[meirman]

In alt.home.repair on Mon, 18 Jul 2005 22:27:34 -0700 Eric posted:

An oscilloscope would be good.

I would take a tv out there and see what sort of picture you get.

I would be especially good to use one that gets a bad picture when connected to the cable inside.

I would connect a known good 9 or 12 inch tv inside to the same place I was getting a bad picture inside and a) see if that tv got a good picture where your bigger tv is providing a bad one; b) if it got a good one, the primary problem might be your regular tv (but don't jump to conclusions.) c) If it didn't get a good picture, I'd take the little one outside, to the cable box you refer to above (you are talking about outside, aren't you?), and see what kind of picture it got there. It's a lot easier to carry a little tv** than a big one. blah, blah, blah. You get the general idea.

**Of course small screen tvs normally give better pictures than large screens do. You'll have to keep that in mind. Or use a bigger one if all your initial testing is inconclusive.

I would also buy a 50 or 100 foot roll of coaxial cable, with ends -- I forget the name of tv cable -- and a female to female coaxial connector, and connect that to the cable outside, and the other end to the tv you're having trouble with inside. Bypass all the interior wires, boxes, and tuners. See how the picture is now. Then connect it to the box closest to that tv and check again.

How many splitters do you have inside? How many tv's connected to the cable? After a certain number, above 2 or 3?, you need a cable amplifier or your signal gets weak. Although I don't like Radio Shack, I'm using two of theirs for the seven tv's I feed directly out of my vcr.

The amps have input and output and an AC cord but no controls. At least one amp only has 2 outputs and was very cheap. The other one is buried under shoes and things in my closet and I haven't seen it for

10 or 15 years. But it works fine.

Length of cable isn't a problem in my experience. 22 years ago when I asked the cable guy to put the channel selecting box in the closet, 5 feet away, instead of next to the tv, he expressed uncertainty that it would work well at such a distance. It worked fine. Later, I had a cable going from the same box down 2 levels through the floors to the basement, 50 feet up to front of the house, 50 feet back and 50 feet up again**, and then up one level through the wall, and the picture was just as good as in the bedroom. And the guy made it sound like 5 feet were difficult.

**For some reason I couldn't cut the wire until I did something else, I forget now. Something to do with going along inside the basement ceiling.

Meirman

-- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.

[meirman]

In alt.home.repair on Tue, 19 Jul 2005 00:11:28 -0700 Eric posted:

You can use most of the advice in my first post to analyse the DVR.

You can also take it the home of someone who can record those channels, on a vcr or dvr, and see how your dvr works there. And maybe vice versa.

And you can discuss it with Comcset.

Meirman

-- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.

[Mark]

correct,

also many cable TV boxes have a service mode where they will display the received signal strength and quality.

Mark

[Edwin Pawlowski]

So why are you bothering with all of this? I had a few problems with my HD stations. Called the cable company and they came out a few times to get it resolved to my satisfaction. They've even called to make sure it was still OK. This is what you pay them for and they wee happy to keep me as a satisfied customer.

[Art Greenberg]

Nope. A 'scope can't easily differentiate among the various signals on the cable (some are not carrying TV channels), and unless its a very expensive model, it won't be any good at the higher frequencies (some cable systems go up to 860MHz).

The instrument designed and built for the purpose is called a "Field Strength Meter." Not something you'll find at Radio Shack.

[Jim Yanik]

Eric wrote in news:OaadnZWMNonbEkHfRVn- [e-mail]:

A Signal Level Meter;it tunes into each channel and measures the signal level,signal to noise level,some even have a TV screen so you can visually check the signal with a known good "receiver".

TEK RFM150 would be one example. Wavetek and other companies also make SLMs.

[Jim Yanik]

meirman wrote in news: [e-mail]:

No,it will not. He wants a signal level meter,specifically made for cable measurements. A spectrum analyzer would help,but not as much as a SLM.

[Walter R.]

If you use a cable modem or black box, most have a built in feature that you can access from your computer. If I type in http://192.168.100.1/ ,I get the current signal level at my cable modem (plus s/n ratios etc.). Mine varies from -3 to -8 dbmv.

Comcast has probably a similar setup. If they have a "help" group, ask there.

A TV is worthless as a signal level indicator. TV frequencies are in the

100-300 MH range, whereas the cable uplink is around 600-900 MH, a different ballpark. You may have great TV reception but your cable connectivity may be terrible.

[Jim Yanik]

"Walter R." wrote in news:sVeDe.16383$ [e-mail]:

A cable modem is not going to tell you that the cable has excessive attenuation at certain bands of frequencies like a SLM or spectrum analyzer will.Modern cable bandwidth is >1 Ghz now. SLMs will also tell you signal-to-NOISE ratio(SNR),another important measurement. -calibrated- measurements. Modern SLMs will measure individual channels,groups of channels,or give you a display of the gain slope for the entire bandwidth. Cable drops are not flat in response,attenuation increases with frequency.

[Tony Hwang]

Hi, You gotta know the password to get into service mode tho. In my city our problem is cable signal being too strong in most neighborhoods. Tony