One could refer to a data book, (SA and Blonder-Tongue have some good ones) calculate drop distance, and determine that a 15 dB reverse tilt is a bad thing. It would take a lot of drop to do that (enough so that an RG11 drop was required). The levels you gave were at the set with the house amp? If so, that means you end up at about neg 15 dB on your channel 78 (gainmaker pilot?) before the amp. This would be a problem too. As an installer, you should be able to come close to determining the approximate tilt by the tap values. Roughly speaking, most architectures these days start at an amp with about a 26 value tap. Given say a 9 dB tilt (could be another value, this is ballpark) that would leave you with about 10 dB at ch 2 and 19 dB at your high channel (depends on system, is it 550, 750, 860, this would be one figure used in how they determined the engineered tilt value also) roughly speaking, the tilt should flatten out as tap values fall in number value. Most systems will end up at the EOL or just before an LE with no more than a 3 dB reverse tilt (but levels would still be sufficient to make your drop length). Some prefer no reverse tilt, it will depend on the engineers approach. So when you reach a tap value somewhere arond an 11 or 8, you will probably be close to a flat output. REMEMBER, YOUR METER IS YOUR FRIEND. Check the tap at the beginning of the job. Levels should be acceptable there. Do the math, at the ground block or at the TV, your result should match pretty close to your data book losses, and keep in mind that the higher the channel frequency, the greater the rate of attenuation will be. Did you look at the tap port closely? One common problem is a broken off stinger from a port terminator, stuck in the boot on the port. Also, some brands of taps are touchy about stinger length. This is a trap that newer installers fall into, when they are trained at a system with a brand of taps that work with very short stinger, and then move into a system where the taps require the full 1/8th inch proud of the hex nut. (I was a rookie once too). Did you try another port? It could be an easy to overlook detail of these sorts. As far as line problems go, was it a house where everything worked fine until the problem occurred? Clues, clues, clues. Or when new services were added? Analog plain 'ol cable can survive a lot. Sometimes things deteriorate slowly over time, and the customer is conditioned by the gradual deterioration, and not realize it. Digital on the otherhand can be a pain. The digital tier may be up high, where the signal is low. The modem downstream may be somewhere in shallower water and be working at it's threshold. Also, if the modem is using QPSK and the digital tier is QAM, you can be fooled, because QPSK will handle more junk than QAM. Make your work habits solid, and don't leave yourself guessing after the fact. Take tap levels before you start, think about if the levels make sense for the tap value you are at. Calculate in your head or on paper what your levels should be at the ground block. Get good at it. It will help you. Also, give the levels you measured at the tap, and tap value if you need to refer the call to a line tech. Honest information will help your credibility, and make you more aware, and better. Sorry for the book, I've been preaching it for years.
>Actually, it's a hardline problem as well as a head-end problem. The plant needs to be "air tight" to have digital work
>properly. A line tech needs to go out and check the whole span from the node to the house. It wouldn't hurt to change all of the cable
>from the tap--pick point-- to the converter. Make sure there are no house amps in line as well. Good luck.
>
>>Did you try to swap the converter? I used to have the same problem with satellite systems. Sometimes it was signal strengths but most of the time it is bad box. (Question is how many times has this box been repaired?). If so was it repaired correctly? Try swapping the box.
>>
>>>I work as a contractor. 2 weeks ago I was given a work order to rewire a house. We went to the house and the customer told us that the problem was that the digital converter was "locking up". We watched the set until this happened, a minute or less. The video froze up but the audio continued. Sometimes the video would catch up on its own. Sometimes you would have to turn the converter off. The customer said they would prefer not to have the house rewired. She asked if we could run a temporary line fron the tap to the converter. We did that, same problem as before. The house was wired with RG-6 so we changed all the fittings and splitters. I called the service manager. He said we had a bad drop. I had explained what we done with a temporary line. He said it was still a bad drop. We changed the drop, same problem as before. I talked to one of the other managers at the office and he asked why we got the order rather than a service tech. He felt it was obvious the problem was not in the house. Channel 3 had 24db signal and 78 had 5 db. There was a 20 db amp in the garage. We removed it, obviously our signal at the tv dropped. We checked the signal at the tap. The were 2 to 3 db higher than we had at the ground block. Today a service tech went out and he called back and said the house definitely needed rewired. A modem that is in the house is working perfect according to the customer. I have only done cable work for a year but it appears to me that the problem is in the plant rather than the house. Any ideas? Thanks
>>
Re:Digital Troubleshooting
Member #: 4915
Registered: 1996-2001
Posted:
42
Name:
Ken Melhorn
Name:
Ken Melhorn
Company:
AT&T Southeast
Occupation:
Lineman
Location:
Louisville, Kentucky
There is 1 reply to this message
