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Cable TV picture is snowy on 1/3 chnls on only ONE of my TVs

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Cable TV picture is snowy on 1/3 chnls on only ONE of my TVs

Postby VEFF on Mon Mar 07, 2005 6:57 pm

I have cable TV.
I have a 4-way splitter (1 in, 4 out) in the garage.

In the master bedroom, there is another 2 way splitter, that leads to a third splitter (15 foot cable length).
From this third splitter the cable (6 foot length) goes into my DVD recorder (pass through) into my bedroom TV. This TV's picture is basically excellent for all cable channels.
Of this same splitter (that the master bedoom TV, which has an excellent picture) there is a 40 or 50 foot cable that runs up the bedroom wall into the attic and then most of the length of the house to another splitter in the attic then back down to living room.
About 1/3 of the channels in the living room have snowy pictures.
All the other rooms are fine...

I could replace the attic cable, BUT
1) that is a bit tedious, although definitely doable.
2) there is no guarantee that the cable at fault isn't the one that runs from the attic down into the living room, in between the wall and the siding (i.e. inaccessible to me).

I was thinking (saw these at Radio Shack) of possibly trying one of the following:
1) a signal attenuator (i.e. amplifier)
2) a signal weakener (for stations that are too strong).
3) signal inteference reducer

Any tips would be appreciated!

Thanks
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Postby smartin4 on Mon Mar 07, 2005 7:26 pm

Not sure if you know anyone who may have one or not, but you may want to put a tester on the line first.

If not, maybe run a length of cable through the house (down the hall or whatever is the most direct route) directly to the living room to see if the cable in the attic is the culprit. Of course, that would pnly be a temporary run to see if the cable in the attic is bad.

You may also want to check all of the connections at all of the splitters & at the tvs. A loose connection or even a bad end on the cable has been known to cause more than a few problems.
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Re: Cable TV picture is snowy on 1/3 chnls on only ONE of my

Postby cfitz on Mon Mar 07, 2005 8:35 pm

VEFF wrote:1) a signal attenuator (i.e. amplifier)
2) a signal weakener (for stations that are too strong).
3) signal inteference reducer


a) An attenuator makes signals weaker. It is the opposite of an amplifier. You probably meant to type:

1) an amplifier
2) an attenuator
3) a signal interference reducer

b) I'm not sure what you mean by a signal interference reducer. Do you have a link?

c) Attenuators and amplifiers are generally broad band and not tunable by channel, at least as far as consumer level products. Thus, you won't be able to apply gain or attenuation to just selected channels. It will be all or none. However, there may be products that have gradually sloping gain curves (higher gain at higher frequencies, lower at lower frequencies) that could help. I would have to check.

d) With the number of splitters you have, I doubt you need more attenuation. Each 2-way splitter reduces the power by half (-3 dB), and each 4-way by one quarter (-6 dB), not even counting parasitic losses. After going through the 4-way in the garage, the 2-way in the bedroom, another 2-way (?) also in the bedroom(?), and finally the 2-way (?) in the attic, you have knocked the power down at least 15 dB to 3% (yes, that is 3/100) of what it was when it entered your home, not counting all the cable loss and parasitic losses in the splitters. Conservatively add another 5 dB for parasitic and cable losses, and your are down to at most 1% of the original power by the time it reaches your TV

e) Snow is indicative of too weak a signal. Interference would show up as ghosting, rolling lines, etc.

f) Putting an amplifier at the TV end of the cable won't help since it will amplify the noise as much as the signal. Putting an amplifier at the input in the garage would help the most, except the power may be too high to amplify there without saturating the amplifier and, thus, distorting the signal. Your best bet may be midway though the cable run in the bedroom.

g) I would first try checking all the connections and cables, as smartin4 advised. I would then attempt to get rid of as many splitters as possible, and make the cable runs as short as possible. Only after exhausting those options would I try amplifiers.

h) You said 1/3 of the stations are noisy. Which stations are they? I am guessing the higher-numbered channels.

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Postby VEFF on Tue Mar 08, 2005 12:21 am

Thanks a lot for the advice guys!!! I really appreciate it.

Here is my feedback (no pun intended :) ):


- Yes, the higher-numbered (i.e. cable such as Comedy Central, which is one of the worst) channels are affected by the issues, although also some lower ones (i.e. some of the VHF 2 - 13 channels) are affected

- Some lower channels do show lines (not really rolling, but almost like a flickering effect and relatively minor snowiness).
Some of the higher (cable) channels come in very well.

Here is some more info (and here are some more questions):
- The attic splitter is feeding two lines, but since I found it to be disconnected, I can get rid of this splitter and just use a coupler connected to the cable droping down into the living room instead (i.e. I didn't miss whatever the other cable coming from the attic splitter was connected to in the house; probably the second family room cable jack, which I don't need or use.
(Note: I originally didn't realize that the cable going to the attic wasn't being fed (i.e. was disconnected); the cable guy tested the TV in the living room on the day I moved and everything seemed / was fine.
I think he only checked a few channels, all of which must have been VHF OTA (2 - 13).
Therefore, when I noticed poor reception (I once again initially checked channels 2,4 7 etc; not even thinking that it might be getting signal OTA)
last weekend, I thought it might be the cable end.
I stripped it and attached the end etc.
I then realized this weekend (after noticing I wasn't getting anything above 13 (other than UHF channels) that something was wrong, went into the attic and saw that the cable wasn't connected.

The strangest thing of all (unless I am going crazy) is that the piece of cable that was cut in the attic was tied to the IN terminal of the 2-out/1-in splitter); therefore when I connected (via a coaxial cable extension) the cable hanging from the attic into the bedroom to the bedroom splitter coming from the garage, I was suprised to see that the TV in the living room started to work with respect to reception of cable channels, even though the wire in the bedroom was connected to the OUT terminal, not the IN terminal of the splitter AND the living room cable was connected to the other OUT terminal of the SAME splitter!!!!!!!

I will take the end (in the attic) of the cable coming form the bedroom (source / in) and connect it to the IN terminal of the splitter (disconnecting the piece of cable that has been cut and is currently attached to that IN terminal); leaving the cable that runs from attic into living room attached to the OUT terminal.

But if BOTH the source and destination are connected to the OUTputs, something seems very wrong - i.e. I should be getting any cable in living room with the way it is connected???


Sorry for the lengthy post; hopefully it makes sense.
Feel free to ask more questions.

I am still puzzled by the "two cables BOTH being connected to the OUT" on the attic splitter.
If that is the case, simply using a coupler, or connecting the one coming from the bedroom to the IN terminal may solve everything.

If not, I could swap out the attic cable (coming from the bedroom) with a new one and hope that was the problem since, as I stated, the one going from the attic down into the living room is impossible to replace without professional assistance; not even sure how cable guy would go about that one).

Note:
I stripped the wire (outer jacker and inner insulation) and attached a new cable end (inside the wall plate) myself (as mentioned earlier in my post) - speaking of the cable end inside the wall plate coming down from the attic, in the living room.
Maybe that wasn't done well enough; I did it as well as I could though.

If only I could ALSO easily replace that one (i.e. not buried behind wall - I know I could pull it up, but if I drop a replacement cable down from the attic, I don't know how I would get it to end up exactly in the right spot without being blocked by beams or other wall hardware, insulation etc. etc. etc).
I know I would be able to solve my problem by replacing that living room cable (behind wall coming down from the attic and/or the attic one coming from the bedroom).
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Postby cfitz on Tue Mar 08, 2005 1:18 am

It is getting hard to visualize how you have everything hooked up from verbal descriptions. You may need to draw and post a diagram at some point.

Anyway, it is possible for the signal going into one output of a 2-way splitter to appear (attenuated) at the other output. Splitters are passive devices and can be equally well used as combiners where you apply signal 1 to "output" 1, signal 2 to "output" 2, and get the sum of signals 1 and 2 coming out of the "input".

For clarity of discussion, I will hereafter refer to the "input" port of your splitter as port S, and the two "output" ports as ports A and B. This reflects the fact that splitters work equally well as combiners, and removes any confusion caused by labeling ports as "inputs" or "outputs", since any of the ports can be either inputs or outputs depending on whether you are using the device as a splitter or a combiner.

Usually splitters/combiners are designed to have good isolation between ports A and B so that even when cabled as a combiner you don't see much of the signal on port A at port B. However, some designs offer better isolation than others, and even high-isolation designs will fail when all ports are not properly terminated.

For example, if you had nothing at all (no cable, no terminator) connected to port S on a 2-way splitter, you effectively have infinite impedance at port S rather than the designed 75-ohm impedance, resulting in total internal reflection of the signal at that port. Essentially, a signal applied to port A travels through the device to port S, bounces off and goes back out port B, losing about 6 dB of power in the process (not counting parasitic losses).

I'm guessing that is the situation you found in up in the attic. So, instead of the 3 dB of loss I estimated earlier, you actually had 6 dB of loss. Add in some parasitic losses and you probably end up with the power at your living room TV being easily below 1/2 of 1 percent of the power coming into your house. And it could be even worse if you have poor cabling, other unterminated devices, etc.

The same advice still holds: clean up your distribution network, get rid of unecessary splitters and cable runs, verify cable and connector integrity, and (I didn't mention this earlier) make sure any unused ports on any splitters are properly capped with 75-ohm terminators.

cfitz

P.S. The easiest way to replace existing cable is to attach the new cable to the old cable with a barrel connector, and then pull out the old cable. Since the new cable is connected to the old cable, it will be pulled into place as the old cable comes out. This isn't foolproof, since there might be kinks or small diameter holes that would catch the barrel connector at the splice between the two cables, but it is a start.

A little electrical tape wrapped around the barrel connector to cover sharp edges can sometimes make it less likely to catch on something half-way down the interior of the wall. It also helps to have two people on the job, one pulling the old cable out at one end and the other feeding the new cable in at the other end. Still, you have to be prepared for potential problems that would require you to break out a drywall saw.
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Postby cfitz on Tue Mar 08, 2005 8:05 am

By the way, when checking the cables, unless you see physical damage (kinks, crushes, nicks, cuts, etc.) it is unlikely that a cable itself has gone bad just due to age. More likely problems include connectors that were never installed correctly in the first place, have loosened with age, or have oxidized on the mating surfaces. Your strategy of refreshing the cables by trimming off the end of the cables and installing new connectors can be good to overcome these kinds of issues.

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Postby CowboySlim on Tue Mar 08, 2005 5:23 pm

Veff,

I've just gone through a mess of trouble somewhat similar to your with three TVs downstairs (one with some marginal channels), two upstairs (one with some marginal channels), and plenty of splitters. Well, then I wanted to add a third upstairs and put a digital box at the downstairs TV with the worst reception and then everything got worse after the cable guy came out to put in the third line upstairs.

The pictures upstairs got worse. Only the closest to the street TV downstairs retained a good picture. Well cable guy didn't have an amplifier with him so he said he'd note that and another guy would come out with him. I didn't notice till after he left that two of the new digital channels didn't come in at all!

Well to more cable guy visits to sort it out. The last guy knew what he was doing. He cleaned up connectors and replaced the splitters. That helped the downstairs TVs and got the missing digital channels back as one of the original splitter was completely the wrong type but didn't do that much harm to analog channels. When he put in an amplifier everything was good after that.

Short message, Veff: Quit screwing around with it yourself and call the cable guy. You've got to have that db meter to see what you've got and where and what to do. Also, I looked at that Radio Shack stuff and backed off - it's a nightmare waiting to unfold. An amplifier is $60 at an electronics store and the cable company provides it for free if needed.

Cfitz has a good feel and good advice but unless he can drop buy with meter..............

Good bye and good luck,
Slim
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Postby VEFF on Thu Mar 10, 2005 8:51 am

Thanks Slim. Good luck!! :)

I am not going to go crazy since it isn't worth it.
However, I will check a few things out and maybe make a few adjustments. I'll check the results.
If it doesn't work I'll call the cable company and see what happens.

I am curious what they (Cablevision) will charge (I hardly use the living room TV - understatement of the year - since I have the bedroom one and the nicest one is in my family room. In addition I might be selling the house this spring to move closer to my new office) and, last but certainly not least, I am also not sure HOW he would get a cable from the attic to the living room BEHIND the walls?

It can't hurt to call them though, if my simple changes, that I already have in mind, don't work.
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Plextor PX-716A same TLA

LiteOn 52246S 52X CD-RW
LiteOn 52246S (another)
LiteOn 52327S 52X CD-RW
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Postby VEFF on Thu Mar 10, 2005 2:11 pm

Update:

Great news:
1) I replaced the splitter in the attic with a coupler (RS gold-plated $1.99; last coupler [gold-plated or otherwise] they had), since it was only connected to one output anyway.

2) I bought an amplifier 10dB ($31) (one input, one output) and connected it via a splitter to the master bedroom AND living room TVs (needed to connect it to both, since they shared one input (and hence a splitter) to begin with.

The picture is very good now for the channels that were the worst (i.e. those that were snowy enough to be annoying before adding the amplifier). The rest are (still) excellent :)

I suppose I could get the 4-way amplifier ($50), to avoid using a splitter which obviously downgrades the signal slightly, but since the 4-way is 8dB as opposed to 10dB for the one-way amp, it may not make any difference.
Any thoughts?

The best part is that it was easy and quick to make these two changes.
Burners only:
Pioneer DVR-115D
Pioneer DVR-111D
Plextor PX-716A TLA0304
Plextor PX-716A same TLA

LiteOn 52246S 52X CD-RW
LiteOn 52246S (another)
LiteOn 52327S 52X CD-RW
TDK 40X USB 2.0 CD-RW
TEAC CD-W540E 40X CD-RW
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