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Posted By: jeffmoss26 Cable TV issues - 01/29/07 05:27 PM
As part of my job here at school, I had to troubleshoot some cable tv stuff today. We have a former restaurant turned general use space in the student union. I would say there are at least 10 tv's hooked up. Previously we had a poor signal which we traced to a bad splitter feeding the room. This was replaced with a barrel connection and the signal was OK. I went to check today as the Superbowl is approaching and they wanted to make sure the tv signals were OK. Well, I checked and they were awful. Snow and poor reception...so I first checked the feed (plugged a TV into the coax) coming into the room from the floor below, and the signal was fine. Then I checked the other end of this run where it terminated and it was fine. The line runs to a distribution box and then an amplifier. I checked each connection, and as it went along from feed, to distribution box, and finally to an amp, it got progressively worse. Keep in mind I was testing in the equipment room and not using the TV's in the actual room. So I deduced that the amp is not good. I have no idea why, but we have to call the TV people in from the school to figure it out. All in a day's work smile
Posted By: bfdatacom Re: Cable TV issues - 01/29/07 07:05 PM
At a residential job in Malibu, reconnecting an old (and I mean old) amp, turned some snowy screens into crystal clear ones. I know that doesn't help you, but the amplifiers are critical when you have that many TVs. I will be installing three at different jobs in the coming weeks. I hope we don't have problems. They are going to be connected to Time Warner and Charter cable systems, and they all need bi-directional because of pay-per-view and video-on-demand.
Posted By: RobertF Re: Cable TV issues - 01/30/07 12:20 AM
And remember with amplifiers, if they get crud in they just spew amplified crud out.

Luckily you can use one way amps for what you're doing, doesn't sound like you have any two way devices being used.

Check all the fittings, they do go bad, and if it's one feeding the splitter, it'd trash all the downline TV's. I look at it this way, if you don't have the proper signal meter, connectors and splitters are a cheap and quick troubleshooting method. If you replace them and there are still a lot of problems, start bypassing wiring with a temporary run one by one till you find the bad sections.
Posted By: twisted pair Re: Cable TV issues - 01/30/07 04:52 AM
Are you sure the circuit supplying power to the amp was working Jeff?
Posted By: jeffmoss26 Re: Cable TV issues - 01/30/07 06:35 AM
I was just checking out the signal with a TV. If anyone repairs this, it would be the TV guys on campus, not me.
Posted By: JBean3329 Re: Cable TV issues - 01/30/07 03:13 PM
Do you have any legs off the amp that aren't being used or don't have TV's connected? Try loading unused connections - I had similar problems aboard ship in my Navy days. Try terming unused connections with a 75 ohm load.
Posted By: Jeff E Re: Cable TV issues - 01/30/07 03:37 PM
Sounds like you don't have a good enough signal coming into the amplifier. I'd keep checking up stream connections. As some have stated, hard to tell what you're doing without the proper test equipment.

I ran alot of mainline cable and did house hookups a lifetime ago, boy I don't miss that at all.
Posted By: jeffmoss26 Re: Cable TV issues - 01/30/07 04:23 PM
The signal coming to the amp is OK. Leaving the amp it gets bad...I think it's time for TV services or the cable company to figure it out smile
Posted By: twisted pair Re: Cable TV issues - 01/30/07 08:32 PM
Quote
The signal coming to the amp is OK. Leaving the amp it gets bad
That's why I was asking if the amp is getting power or not. If the amp has lost power it actually makes the signal worse. I'm always amazed at how many think that if the amp is unplugged, it just bypasses or is a straight through signal.

Very few amps out there have power indicators (other than the Electroline brand, which IMO are the best) so you will have to check the receptacle.
Posted By: hbiss Re: Cable TV issues - 01/30/07 11:45 PM
Typical computer guy. :bang:

They actually do make test equipment such as a signal level meter for this you know. You are just wasting your time by using a TV.

If it is your job and your school want's you to do this then they need to get you the proper equipment AND you need to learn how to use it! Might even be a good idea to incorporate it into the curriculum instead of all that computer stuff. You might even learn something useful.

-Hal
Posted By: RobertF Re: Cable TV issues - 01/31/07 12:57 AM
Quote
Originally posted by JBean3329:
Do you have any legs off the amp that aren't being used or don't have TV's connected? Try loading unused connections - I had similar problems aboard ship in my Navy days. Try terming unused connections with a 75 ohm load.
Good point. Terminating unused ports and connections is a rarely done practice on the low voltage side for some reason. Simply closing the system can solve numerous problems caused by ingress into the system. You certainly don't HURT anything by having it all properly terminated.
Posted By: jeffmoss26 Re: Cable TV issues - 01/31/07 06:52 AM
Yes Hal, I know they make proper test equipment. Also, there are splitters with open ports that should be terminated. This is one of those 'take a look at why it doesn't work' type of deals...there isn't a whole lot I can do, because the campus has their own cable TV people. Believe me, if it was up to me, I would re do the entire thing. My hands are pretty much tied in the matter.
Posted By: jeffmoss26 Re: Cable TV issues - 01/31/07 01:55 PM
EDIT
We got everything working. Bypassed the Amp and went straight out to the TVs. It all works fine now.
Jeff
Posted By: hbiss Re: Cable TV issues - 01/31/07 08:03 PM
Actually open splitter and tap ports happen all the time and not by mistake. Of course it's good practice to put terminators on unused ports but an unterminated port results from every jack not connected to something. When was the last time somebody put terminators on unused wall jacks? Even if you did they would never stay there.

Fact of the matter is the terminations (or lack of) will not affect the signal levels. Open ports can contribute to signal leakage which may get the cable company in trouble but that's about it.

Bypassed the Amp and went straight out to the TVs. It all works fine now.

Or so it seems. That amp musta been there for some reason don't you think? Like I said, TVs don't make very good signal level meters.

-Hal
Posted By: twisted pair Re: Cable TV issues - 01/31/07 08:20 PM
Quote
Fact of the matter is the terminations (or lack of) will not affect the signal levels. Open ports can contribute to signal leakage which may get the cable company in trouble but that's about it.
However it's a place where outside interference can leak into the system.
Posted By: hbiss Re: Cable TV issues - 01/31/07 11:22 PM
Yes but that little bit is unlikely to cause any problems since the return carrier level has to be quite high.

Used to be that ingress was a big problem when it leaked into feeders and trunks. That problem has been eliminated with fiber.

-Hal
Posted By: twisted pair Re: Cable TV issues - 02/01/07 05:20 AM
I had a situation like this happen (which is what makes me ensure terminated ends now).

Customers were retired seniors, she complained about noise bars in her TV all day and her husband had a hobby woodworking shop in the basement. He only worked in there during the day and the TV was fine at night.

I found a coax hanging in the shop (that was prewired for a wall mount set) was picking up the noise from the machinery. I screwed a female to female coupler and a 75 ohm terminator on, problem gone!

I also see this a lot on CCTV systems with unterminated loop backs and monitor outputs. Of course like Hal stated, the original carrier is weaker in this case so it doesn't take as much return ingress to cause noise.
Posted By: Jeff E Re: Cable TV issues - 02/01/07 09:59 AM
When using terminators on amplifier ports, just make sure that the amplifier is NOT passing power through it, I terminated a long run one day and had forgotten to place the power plug in the correct position, I made the whole cable system snow. :shrug:

I finally realized what I had done when I went back to the terminator to make a test and burned the heck out of my fingers, those resistors can make quite a bit of heat!! eek
Posted By: hbiss Re: Cable TV issues - 02/01/07 10:25 AM
They do make power isolated terminators as well as splitters but yes, the correct way is to not power the output if it's not needed.

Twisted Pair- I think if you analyzed that situation you would have found problems such as low or marginal signal level and/or an abortion of cables and splitters. Something like that just can't happen when things are done correctly even with unterminated runs. This is why I stress test equipment and knowing what to look for. Judging proper operation with only a TV and no knowledge of proper design is not going to cut it.

I also see this a lot on CCTV systems with unterminated loops...

Different story, that's video and all loop through ends have to be terminated.

-Hal
Posted By: jeffmoss26 Re: Cable TV issues - 02/01/07 04:52 PM
Yeah I am still not sure what the problem is...the TV guy came today and gave us another amp to try. I put it in, and the signal was still horrible. Took the amp out, and it was fine.
Posted By: anthonyh Re: Cable TV issues - 02/01/07 05:44 PM
Jeff did your school upgrade to digital cable? Just a thought maybe the amp is not passing the entire bandwidth
Posted By: jeffmoss26 Re: Cable TV issues - 02/01/07 07:14 PM
We just have regular cable everywhere.
Posted By: Rover88 Re: Cable TV issues - 02/02/07 06:12 PM
One of the problems we find is that sometimes tha amps are pumping too much power into the system. A 40db amp can be cranked to put out 46 db or better at the output. The length of your cable run will attenuate the signal somewhat, but without a signal level meter you're just guessing. I'm not sure of the exact number (I'd have to ask my son), but I suppose you want to have 10db or less at the set. We've tried to bypass the amp to clean up the signal temporarily (before we bought a signal level meter) and it sort of works with analog sets. Won't work with digital, which are much more particular about their level.
Posted By: hbiss Re: Cable TV issues - 02/03/07 05:18 AM
Rover is correct. Too much signal is just as bad as too little. Also, the position of the amp is important. It needs to be at the begining to "push" not where the signal already down in the dumps and it's noise figure comes into play.

The range you want each set to see is 0 to +10db. Actually "digital" is much more forgiving. An analog set will gradually turn to snow as the signal is decreased and is subject to interference. Digital will maintain the same picture quality down to a point then it will pixilate then nothing.

-Hal
Posted By: Jeff E Re: Cable TV issues - 02/03/07 06:46 AM
We always targeted for a +3db at the end of the customers drop since our company (in the old days) charged for extra sets connected to the system. That way if the customer installed a splitter and multiple runs of coax they had lousy signal. This was done by installing the correct tap at the mainline splitter.
Posted By: hbiss Re: Cable TV issues - 02/03/07 02:20 PM
We always aimed for +10 so that we could install a 4 way if necessary.

-Hal
Posted By: Jeff E Re: Cable TV issues - 02/03/07 06:12 PM
We charged for a 4way, back in the bucket I went laugh
Posted By: CCSGINC Re: Cable TV issues - 02/04/07 12:45 PM
Jeff,

As a response to your posting regaurding the FIX.

I wanted to mention the Input signal to the amp. If you were able to bypass the amp totally and feed out to the TV's and get good pictures, your problem was probably "Overdrive" at your amp.

Too much signal hitting any "Active" device will cause a worst picture than LOW signal.

Also, as mentioned, with proper signal meters and sweep equipment, these problems can be identified fairly quickly.
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