ECN Forum Forums General Topics of the Trade General Discussion Area Cable Television signal testers

With cable service suppliers going digital, they are offering more services today, then just TV, with that said inside cable wiring is more critical then it was in the past days of analog signals.

Actually it's not. All you are talking about is one cable modem and that should get connected before any distribution where the service enters the premises, and that either works or it doesn't with a wide latitude unlike an analog TV receiver.

For Joe and LK- again that's not our job! Matter of fact the state of Connecticuit has separate licensing for cable TV and MATV installers and techs. It's not even part of the electrical board of licensing and if you want to do this kind of work, whether you are an electrician or not you have to pass that test and obtain that license.

I believe the reason for this is because Connecticuit recognizes the fact that this is an area that requires specific training and experience beyond what would normally be expected of the electrical or any other trade that may be interested in doing this kind of work.

I can understand everybody wanting to get into this area but for most that means no better than a DIY job. If you want to take care of your customers do them a favor and either learn the trade or leave it to someone who has.

-Hal

My brother's house has 3, yes, three digital devices, 2 digital cable boxes and 1 modem.

The digital cable boxes function very much like a cable modem with a return band below 50MHz and QAM modulation for the downstream channel. (In fact, you'll find that as the cable modem boots up, it stops on all of the digital cable data carriers, checking to see if they're the downstream for the cable modem).

Problems which affect the cable modem WILL affect the digital cable boxes.

I see people like to use the "digital" catch phrase. Truth is that cable you screw onto the back of that digital cable box and modem is analog RF and probably half of the cable channels are not digital at all. Nothing is new or more critical here except that there is a return carrier that must be taken into consideration.

You will find that the digital channels are actually much more forgiving of things like low signal levels, reflections and interference due to the method of encoding. As signal levels are reduced you won't get snow but beyond a certain point the picture gets pixilated then nothing.

I dare say that if it seems like there are more problems it's because more people rely on cable now and for more than just their expensive TVs. Everybody thinks they are a cable installation expert and that's where the problems come from. Doesn't matter what test equipment you have or what cable and connectors you use if you don't know what you are doing to begin with.


-Hal

[This message has been edited by hbiss (edited 11-15-2005).]

Yes, the return carrier must be taken into consideration.

Problems with the return carrier, which are mostly caused by ingress from poor installations, can be very difficult to track down, especially if they are intermittent.

I recall reading about one case where there were intermittent outages caused by upstream interference strong enough to clip the upstream laser; they eventually tracked this down to a poor installation picking up interference from a nearby ham radio operator. (Legally, the ham radio operator was not responsible for the interference).

At one point, some cable companies had a policy to install high-pass filters (which filter out frequencies below 50MHz) on drops of customers who were not using any services which require the return band. Perhaps some still do, but in this day and age where people want to buy the cable modem at Best Buy and plug it in and have it work that day, probably not.

One of the big problems with troubleshooting digital is that it's "all or nothing", wheras with analog you can tell from the picture whether there's a problem and how much of a problem it is.

Case in point: If I have an analog TV connected to cable and it's on channel 18, I can tell from looking at the picture whether there's an ingress problem. Why? Because pagers operate in the same frequency band and will result in an intermittent herringbone pattern (when the paging tower transmits).

Try doing THAT with a digital cable box with a digital carrier on channel 18.

(One could, I suppose, make the argument that such ingress will not cause problems with the cable signal on channel 18, but that would be a case of not seeing the forest for the trees; ingress which is visible on channel 18 is indicative of a problem with the installation that could affect any channel or any service at any time depending on what signals happen to get inside the cable by the same fault that allows the pager signals to get into the cable)


[This message has been edited by brianl703 (edited 11-15-2005).]

[This message has been edited by brianl703 (edited 11-15-2005).]

Here is a URL that might be useful:
http://www.ct-magazine.com/archives/ct/1099/ct1099j.htm
http://www.ct-magazine.com has quite a few articles about the technical side of cable TV.

Brian, thank's for the tip on that magazine. I just signed up for a subscription.

-Hal