Any Comcast guys around?

[sfav8r]

We are doing some electrical work an apartment. While we were there, the owner says Comcast was out and told him that he has a good signal at a j-box in his apartment, but the cabling from the j-box to the jacks needs to be rurun. The strange thing is that he has a perfectly good picture right now. They told him that the reason he can't get digital is the bad cabling.

The cable coming in RG6 and the cable to the jacks appears to be RG6. I,ve never actually seen cable like it. It is a translucent blue and it is stamped INMAC 79733. It looks like RG6. It is definately not RG59.

At any rate, my main question is, how can I tell if I am getting a good enough signal for digital? The H/O does not have a digital box on-site for us to test with. Is there some other way to test? Any thoughts on what the cable could be? Suggestions? Winning lotto numbers maybe?

 

[ike5547]

Could be a bad splitter.

 

[e57]

Not the cable guy - but... I usually use RG-6Q - often they won't touch anything else if it is in the wall, and often remove anything else that is not RG-6Q....

As for testing for digital..... ?????? Maybe they qualify it in some way? But that may even include the OUTSIDE wiring too IMO....

 

[zbang]

Divide and conquer (at the spiltters)? You'll need a test box of some sort to really do this. Also- it's really INMAC cable? They merged with, IIRC, MicroWarehouse, in the '90s. There ought to be some othe markings on it, but I doubt that it's RG-6 equivalant.

 

[danickstr]

http://www.globaltestsupply.com/c/1...Cable_TV_Signal_Level_Meter_and_Analyzer.html

 

[petersonra]

I once had this chat with a cable guy. He said the digital cable signal is very sensitive to the type of cable and the type of connectors used. They have some kind of box they hook up to see if the signal is adequate. If the box says "no go", most of the time they run new cable and connectors.

 

[MacG]

I once had this chat with a cable guy. He said the digital cable signal is very sensitive to the type of cable and the type of connectors used. They have some kind of box they hook up to see if the signal is adequate. If the box says "no go", most of the time they run new cable and connectors.

FWIW it is my understanding that it is getting to be things like even if the bend radius is too tight it can affect the digital signal. Of course now, I don't remember what the minimum bend radius is but have you ever seen where the cable goes through a hole in a stud at 90 degrees that has been pulled tight? I think it is about a 4" depending on he cable specs.

Something else that can have a negative effect on the signal is stapling or cable tied bundles that indent the sheath and shield below especially when there multiple staple or ties that are measured out evenly like every 6 inches or another even increment. Best practice is to not indent the cable and space the fasteners randomly with in a given range say 6-8 inches. In racks use Velcro straps/ties for cable bundles.

Another thing that comes to mind any length of cable is a 75 ohm system that is less than 18" is no longer 75 ohms and that can mess things up too.

MacG

 

[Speedskater]

Another thing that comes to mind any length of cable is a 75 ohm system that is less than 18" is no longer 75 ohms and that can mess things up too.

MacG

The characteristic impedance of a cable is calculated for an infinitely long cable. The shorter the cable the less impact on the signal of any incorrectly terminated cable. For a correctly terminated cable an inch is as good as a mile.

 

[wireguru]

another thing that wreaks havoc with digital cable is if the center conductor is nicked when the cable was stripped. The high frequencies ride on the surface of the center conductor and if its nicked the nick deflects the signal.