Cable Signal Degredation Question?

E

Elijah

Limp Gawd
Joined
Dec 4, 2004
Messages
175
Here goes.

We have a main cable coming in outside and it is now split into 4 different cables running to different parts of the house.

1 TV
1 TV
1 Internet
1 HTPC Setup.

I am wanting to get the PVR-500 MCE but do not know if I can yet again split the cable I just ran for the HTPC setup.

How does this stuff work? If the 2 tv's arent using a signal will the others have more bandwidth?

The splitter is a generic 5mhz -1ghz.

So If I split the HTPC signal yet again to benefit the 2 channel pvr 500 mce will I just get a crappy picture on both inputs?

Would it be better to just split the original signal into 5 signals vs split 1 of the 4 into 2 ?

Thanks for any input.

Oh by the way I ran quad shield RG-6 if that matters at all.
 
What I am assuming based on the info is that you have one splitter box with four outputs on it. A standard (meaning 99.9% of them) 1->4 splitter has an 7.8 (referred to as 8)db signal loss on all four ports. If you were to further split the line further as you are suggesting with a two way splitter, which would be generally 3.5 (4)db loss on each port, that means the signal coming into your HTPC would be -11.3 (12)db from the original signal.

Visible quality loss on several analog frequencies/channels generally begins around 6-8db (according to my personal experience), so here is the solution - an amplifier. You can get a 5-900mhz (you need one that goes the full range to avoid problems) from any walmart for around $20, and I beleive that one is around +12db (i've got one here, would have to look). You simply place it inline - but the location is vital.

Think of it like this - say you have a TV signal that is 50db, and you run it through the first 4 output splitter, and place the amplifier inline between it and the next 2 port splitter that you added for your HTPC. You have a 42db picture after the first the splitter (8db loss). If it then gets amplified that by +12db, you'll have a 54db signal that only has the quality of 42db. The final 2 way split after the amplifier would take away 4db from that, leaving a 50db signal that has the quality of the 42db signal that existed right before the amplification. The first split permanently cuts into the image quality, because you cannot simply add a better image to the line by increasing the signal strength. Kind of like how you cannot simply re-encode a low quality mp3 to a higher bitrate and expect the sound quality to improve.

Now, if you put the amplifier before the 4 way split (which may be hard depending on location), you'll have a 50+12db = 62db signal with a quality of 50db, identical to the original signal. As it passes through both splits along the way to the HTPC it looses 12db, but you are right back where you started with a 50db signal of full quality - the splitters just knock off the overhead.

So in short - get an amplifier (the better quality the better results, but a cheap walmart one should be fine) and put it before any splitters right at the original line. You might have trouble getting your cable modem to connect if you get a really cheap one, so be prepared to invest a bit more ($50 or so) in a qualtiy one if a cheap one dosen't work out. My walmart one worked pretty well, although I end up ditching it because my wiring layout changed to where it isn't really necessary.

But then again, your cable distro unit in the yard might be stronger than mine, and you may be able to do multiple splits without any fuzzy/bad channels or image problems. But an amplifier is generally considered to be the correct answer.
 
Nice, thanks for the feedback

So now I get a amplifier a $50 one, no prob. Put it before my splitter. Then my line coming into htpc box is still around 50 db. Now I can split it into 2 channels off the same line and it will probably only have 3.5 db signal loss right and that will still give a good picture??

I probably won't be able to see the difference but if I am recording it i want to get the best recording.

Thanks Again for you help.
 
If the signal/picture quality are ok to begin with I wouldn't bother with an amp. Just split the line where you have the capture card. If the signal is crappy after that, then worry about a small signal amp.
 
Yeah as I said, you might be ok - try it first. Only go with the amp if the quality is down, some people end up having strong signals in the first place and not needing one.
 
k1114 - Just wanted to say that is a very good post detailing how to handle splitting a signal. Almost should be made a sticky.
 
I ordered the motorola signal booster anyway, just have to figure out how to get power to it now.

We will be wanting high def pretty soon in everything and we have 2 computers on high speed 3 mbit.

It won't hurt anything and some of our analog signals (channels) are kinda crappy anyways.

Yeah that would be a good sticky.
 
You must log in or register to reply here.
Back
Top