Question for the TV cabling gurus

[nsafreak]

Ok I'm trying to figure out just what's wrong with my cabling setup as it is right now. As it stands right now the TV sets in my house are getting a good signal and a good picture. I want to add my PC to the mix as I do have a TV tuner card for it. There is a cable outlet near it but currently there is not a signal being fed to it. The main reason being it used to be fed from a splitter which I have removed from the loop. If I added the splitter the signal is too weak and the picture on my TV that's on the other part of the split goes to crap, if I run it straight through though the picture is of course fine. I thought about splitting from the VCR since the TV isn't too far from the computer and I'm running the composite out from the VCR to the receiver for video & audio. The problem is that when I attempted to run a coax from the TV out of VCR to the TV card I saw a nice blue spark (quite large) when I was about to hook the cable into the tuner card. That obviously won't work as it'll surely fry the card and damage my PC. So what is my best option here?

• -Add an in line amplifier before the splitter? If so how strong of an amp should I use?

• -Use some kind of amplifier/splitter combination instead of the one I have now?

• -Get a better splitter? The one I have now looks decent, it's made by a company called Regal

• -Some alternative method?

Your help with this is appreciated folks.

 

[morkinva]

I'm concerned with the spark; is the pc properly grounded? If the cable line was installed properly it will be grounded to a water pipe. Either way you're gonna have to hook up to the pc card, so I'd address that first.

You can buy one of those outlet tester things at home depot for about $5.

 

[nsafreak]

As far as I know the PC is properly grounded. I run the critical PC components (PC itself, monitors and network equipment) into a TrippLite SMART 1400 UPS and the non critical components run into a surge protector. Both the UPS and the surge protector show that they are grounded. I should also mention that I recently had an electrician out to the household to do some wiring checks, he replaced a few outlets and did check to make sure they were grounded, these outlets include the ones in the PC area. I'm not sure where to check for grounding on the cable though. It comes from the ground into one junction box, from there it runs to various lines & splitters throughout the house. Is there a place where I can use a tool to check if the cable is grounded? Also one other thing I should note is that a few months ago I lost the cable to my TV set and this other outlet. The cable tech that came out ended up replacing the splitter that used to be present and putting a new connection on one of the cables. He said that another one of the TVs in the household was sending extra voltage down the line and that was what fried the splitter. He said he put in a splitter that had a higher impedance (I think that's the proper term) so that it couldn't happen again. Is there some kind of test to find out which TV is doing this or is he feeding me a line of bull?

 

[Crusty]

What frequency range is noted on your splitter?

 

[nsafreak]

Here's what the splitter has on it:

Frequency range: 5-1000 Mhz
120dB EMI Isolation
2-Way splitter

 

[Crusty]

That's a fine splitter, shouldn't have any problems with that. That is unless it is all corroded and crap.

 

[nsafreak]

Nope splitter looks like it just came out of the package, nothing on any of the ends. Seems like I'm dealing with a weak signal going into it though.

 

[Mday]

some questions:

are you using digital cable or sat?
why am i asking this? frequency response of the splitter must match the signal. also, digital cable requires duplex communications, which can get screwed up if you use an amplifier.

are you using a separate decoder box for the PC+tuner?
why am i asking this? if you do get a separate decoder, the cable company will supply you with a proper splitter (which may or may not have to be returned to them) as well as do any work necessary.

is the cable split anywhere inside your apt\house?
why am i asking this? this leads to splitting a split connection (that's bad). it's better to replace the splitter with one that can ouput more (non used ports should get terminators)

those 3 questions are independent, and solutions to each can interfere with others.

if everything is "fine and dandy" here's how the wiring typically goes:
cable into your house goes into a amplifier with multiple outputs or before the splitter if using a single output amplifier.
any ports NOT BEING USED in any splitter should be terminated.

an alternative:
if you're using a single tuner for both the PC and the TV, use the video cables (svideo or composite) to transfer video if the tuner on your PC has such an input. also, reminder that a tuner is not a decoder. and make sure everything that should be grounded IS grounded properly

 

[nsafreak]

are you using digital cable or sat?
why am i asking this? frequency response of the splitter must match the signal. also, digital cable requires duplex communications, which can get screwed up if you use an amplifier.

Plain old analog cable. When I do get satellite I plan on eliminating the splitters entirely.

are you using a separate decoder box for the PC+tuner?
why am i asking this? if you do get a separate decoder, the cable company will supply you with a proper splitter (which may or may not have to be returned to them) as well as do any work necessary.

Nope just using the built in tuner on the card

is the cable split anywhere inside your apt\house?
why am i asking this? this leads to splitting a split connection (that's bad). it's better to replace the splitter with one that can ouput more (non used ports should get terminators)

To the best of my knowledge there are a total of 3 splitters in the household. Although I may be missing some that I cannot see.

There is one in the main junction box, one on the outside of the house with a feed from the junction box (two way splitter) and one down in the basement which is another two way splitter. All of the ports on the splitters are being used currently so there is no need for terminators on them. Is there an outdoor amplifier that you would recommend using?

Also is there some way to test and see if the cabling is grounded when you can't visually see where the cable is grounded?

 

[morkinva]

This is the thing I have near where my cable comes into the house. From one of the screws is a green wire than goes to a clamp strapped around a water pipe.

I suppose you could take a voltmeter between the metal connector on the incoming cable and the water pipe and you should get close to zero volts.

edit>> I've seen them outside of houses as well

 

[nsafreak]

That's an idea, I'll take a look at where the cable comes into the household in the morning and see if there's something like that present.

 

[nsafreak]

Ok I think that the system is grounded although I'm not 100% sure of that. Here are some pics of the junction box and what I believe is the grounding wire.

Junction box
Ground wire

I noticed the connection was loose when I opened the box so the cause of the sparks may now be fixed. However that doesn't give me a stronger signal from the splitter. I have also looked in depth as to how many splitters there are, there are 2 splitters from the junction box total. Unfortunately I cannot remove them at this time. Ideas how to best improve my signal strength?

 

[nsafreak]

Anybody?

 

[Pepsi90919]

 

[TechnoKid]

Read this: Cable FAQ

That three way splitter is, at the least, losing 5db per leg, thats if it is a balanced splitter. If it isn't a balanced splitter, then you would have one leg with a loss of about 3.5db, and the rest are higher. The cable company will use an unbalanced splitter because say you have two tvs and one cable modem; the cable modem needs the least loss (the -3.5db leg).

If you need to add an amp, you'd want to do so before any other splits in the signal. If you have a cable modem, run the signal from the street into a two way splitter, and one of the two ports use for the cable modem and one of the ports use to hookup to an amp, and the output on the amp hookup to a splitter. This way, the signal to the cable modem has less insertion loss. There is an amount of insertion loss for everytime you split the signal; even if you add an amp to boost the signal after many splits, the cable modem wouldn't work because all those splitters have added return loss, which is basically loss on the return signal from your cable modem.

That FAQ should answer all you questions, and gives several wiring examples.

 

[nsafreak]

Well I'm having NO luck with the amplifier unit here so I'm wondering if I would benefit from using a different splitter. The splitter that's outside has a db loss of 3.5 on one leg and 7db on the other two legs. Where would I purchase a 3 way amplifier with 3.5 (or less) db loss per leg? Because I purchased a 25 db amplifier put it before one of the other splitters where I'm getting a clean signal before hand and it doesn't boost it enough.

 

[Vette73]

Just because the splitter looks good doe snot mean it is. Try another one or even 2.

 

[nsafreak]

Do you mean the two way I'm working with now? I guess I could do that although I'd be suprised if the splitter is no good since it's no more than a couple months old.

 

[bmacd]

here's my suggestion even though you won't do it:

1) put a 2 way splitter on the line that comes into the house. Run one of the split ends directly to your computer. The other end should run to an amplifier. From the amplifier, hook it up to a distrobution block. Then split your coax off as needed.

-=bmacd=-