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Discussion Starter #1
I recently purchased an HDTV (Toshiba 65HX81). I currently am subscribed to cable, and the incoming signal is being split 4 ways in my house.


The signal was not very good, so I went out to radio shack and bought a 4 way amplified splitter. Some channels now are just plain awesome, for example HBO and ABC. However, some channels, notably CBS and NBC have a noticeable pattern on the screen (I think I would describe it as a herringbone pattern). It isn't terrible, but now that I notice it, I REALLY notice it.


The radio shack splitter lets me adjust the gain, and it seems best when I have it on the minimum setting. Increasing the gain makes things look worse.


There is also another switch on the unit (I forget what it is called), which the manual suggests using if there is a herringbone pattern, but the problem persists with either setting.


Does anyone have any suggestions (other than simply removing all splits - my wife would kill me)? Is there a better amplified splitter on the market? Is there another option?
 

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An amplified splitter is not usually required to split a cable signal 4 ways. It can often add more problems than it fixes. Splitters vary a lot in quality as do cables. You need to run a few tests to determine exactly where the problems are. Take your primary set and connect it directly to the cable. You should receive all channels clearly with no herringbone. If not you either have bad cable or there is a problem with your incoming signal (unlikely). A high quality 1:4 splitter should say that it is good to 1 GHz or even 2 GHz. (1 is more than sufficient. All of the lines need to be connected when using a splitter or you need to have a 75 ohm termination (available at Ratshack) attached on the unused lines. These are cheap so buy some to help run your tests. Take a close look at the cable you are using in the house. If it is not a high grade of RG-6, then consider redoing the cable. Connectors should be crimped onto the cable and not the screw on variety. You may have to purchase a Crimping tool at Home Depot or Radio Shack. The Crimp tool is about $15 (a lot less than an amplified splitter) and it has heavy black jaws. Do not get the cheap stamped crimping tool. Use the same type of connectors the Cable company uses.


Normally a herringbone pattern is caused by an interfering signal at a close frequency. This can come when you have a VCR where you are taking the Channel 3 or 4 output and routing it near other cables. Try turning off various other pieces of gear to determine if one of them is causing the problem. When you find the culprit check its cable and connections. Connections need to be VERY tight. Loose connections cause signal loss which in turn will wind up where it doesn't belong. Let us know what you find.


..Doyle
 

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Sounds like overload to me. The switch is usually for reducing FM interference, might try it, but on the cable it usually isn't an issue.


Radio Shack used to sell a variable attenuator, place this on the input to the splitter (from the cable) and adjust it to the point between where the picture gets "snowey" and the herringbone patterns occur.


Bob Smith
 

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I have used several different R-S signal amplifiers in a very similar situation. One cable or antenna feed and 2 to 4 TV sets. Each split causes a signal loss of at least 3 db. Multiple splits could lose 10 db of signal or more.


Some R-S amplifiers create a herringbone pattern and some don't. This is based on the personal experience of yours truly. This is one area where you don't want to try to save money. I got a R-S low noise cable amplifier (about $60, instead of the $15 to $30 models) and it works perfectly, no herringbone. My guess is that the cheap amplifiers have non-linear behavior. The non linear amplification could cause false signals due to interference between adjacent channel signals in the cable. The experts are probably chuckling at this explanation. But that's my theory.


The good thing about R-S is, if something doesn't work you can take it back.
 

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Discussion Starter #5
Thanks for the replies. It's been a busy weekend and it has taken me a while to get back here.


First, let me say I realized that I gave an inaccurate picture of my cabling in my first post. Here is the real story:


Outside the house the cable is split 3 ways (not amplified). One of these outputs goes to a cable modem, the second goes to the basement, and the third goes to a bedroom that is inaccessible from the basement.


The line to the basement is the one on which I now have the amplified (four way) splitter. One of the output lines from this basement splitter is the one that goes to the big TV that I really care about.


First I tried terminating the one unterminated output from the (amplified) splitter. No change.


Next, I tried removing the second (amplified) splitter, and configured the cable so that the line that comes into the basement then goes directly to the big TV. With this situation the picture is snowy. Not terrible, but still unacceptable.


Next I tried sending the cable directly to the TV, rather than through the VCR first. No difference, still snowy.


So then I went back to Radio Shack and got a variable attenuator. So far, it looks like this may do the trick. I haven't had a change to play with it much yet, but with just a little effort I have been able to adjust it so the herringbone pattern is gone (or very minimal - I haven't been able to detect it yet).


I'm not sure the picture is quite as crisp as it was without the attenuator though. I haven't been able to do enough tests yet to tell if this is my imagination or not.


However, for whatever reason my Cinemax reception still stinks. It is very snowy. It is the only channel that has any problem. I should point out that I am not paying for either Cinemax or HBO, they just showed up a while back, even though I never ordered them. HBO looks great, but cinemax looks lousy. I assumed that this was due to the splitter issues, but it could be something else.


So anyway, this is where I am at now. I will continue to play with the attenuator to see if I can optimize the image.
 

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If my understanding is correct, you get one channel very badly and all the rest OK. If so, your problem is not your wiring, amplifier or attenuator. It is the signal on that channel. Perhaps I am stating the obvious.
 

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Discussion Starter #7
Quote:
Originally posted by Mike2567
If my understanding is correct, you get one channel very badly and all the rest OK. If so, your problem is not your wiring, amplifier or attenuator. It is the signal on that channel. Perhaps I am stating the obvious.
No, the problem is not (just) the signal on the one channel, as I will explain below.


Note, I was also having problems with several other channels. The attenuator/amplifier solution seems to have fixed those problems fairly well.


As best I can tell, the one problem channel is Cinemax. The following is a summary of the best picture I can get with the configurations I have tried.


This is a summary:


No Attenuator/Amplifier:

Cinemax - Slightly snowy. But quite watchable.

Other channels - range from good to moderately snowy


Amplifier only:

Cinemax - slight herringbone. Still watchable.

Other channels - mostly very good, but a couple important ones

with slight herringbone.


Amplifier with attenuator:

Cinemax - very snowy. Not watchable.

Other channels - pretty much all good


The last data point above was the most surprising. All the other channels look decent. The herringbone on the other channels is gone. But Cinemax goes to crap. This is true regardless of the setting on the attenuator.


If I have to live with my current options, I will probably opt for the amplifier only. I think I will try your advice and see if I can get a better amplifier. It seems like there is probably a (near)perfect gain setting for my situation, I'm just not quite getting it with the current equipment.


Oh well, the quest for the perfect picture continues...
 
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