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Discussion Starter · #1 ·
Hey guys, new to the board and need some help if anyone has time...


Ive just bought a new house and had my cable/internet installed. When i hooked up the HDTV box, the channels didnt look quite as clear as they did at my last place. I went downstairs to see how it was all set up and noticed that there is one main coming in to a 2-way (cheap) splitter. One leg of the 2-way was going to my cable modem and the other to an 8-way (another cheap) splitter.


Through a bunch of research i have landed on this site and have seen that others have had similar problems and have been able to solve them... i have found my way to the modem diagnostics page and have found the following for the setup listed above:


Downstream:

Frequency 663000000 Hz

Signal to Noise Ratio 36 dB

Downstream Modulation QAM256

Network Access Control Object ON

Power Level 4 dBmV


Upstream:

Power Level 46 dBmV


Now, just as an experiment - i switched two of the cables so that my 2-way splitter now feeds my HDTV box and the 8-way, with the cable modem hooked to the 8-way. With this setup, i got the following:


Downstream:

Frequency 663000000 Hz

Signal to Noise Ratio 35 dB

Downstream Modulation QAM256

Network Access Control Object ON

Power Level -5 dBmV


Upstream:

Power Level 55 dBmV


Does anyone know how to interpret these numbers or know if they are good/bad, what i need to make it better? I was looking at getting an electroline 8-way drop amp and hooking everything up to that, or keeping the modem on a 2-way and hooking everything else up to the drop amp... do i even need one? I will have 2 HDTVs, a cable modem which controls my phone as well... and the rest analog TVs. Any help would be appreciated!
 

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Discussion Starter · #3 ·

Quote:
Originally Posted by lorenkoeman /forum/post/12878524


Check this recent similar thread first, if you have further questions I would be glad to help.

Thanks Loren, I appreciate the help... actually, that is the thread that made me turn to this forum... Problem is - i dont really know how to interpret the numbers that i am getting from the diagnostic page. Also, Im not sure if i am just being a "picture snob". Sometimes i sit back and think to myself "ahh this isnt that bad, but other times i look at it and think "man, i know this can look better". Other problem is, i dont know if the drop amp will even make a difference. I have done a lot of research over the last 24 hours and have decided to buy the Motorola BDA-S4. I think i am going to leave the 2-way splitter off the main - with one leg going to the modem and the other going to the 4 way Motorola, since i really only have 4 TVs in the house right now anyway - i am going to cross the bridge of expanding when/if i get there.


Do you think the numbers that i posted earlier merit buying the BDA-S4? Hopefully you say yes, cause i already bought it - haha.
 

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Correct me if I am wrong, but since your HD box is a digital box, you are not going to get a better picture by upgrading the wires. With digital, you either get it or you don't. Sometimes if the wiring is bad the signal can degrade and you might have drop-outs or horrid "digital artifacts", but it's not like analog in which you have many different degrees of fuzziness, etc.


So as long as you are not getting drop-outs and bad pictures, you are getting the best picture you can get from your wiring.


If this is wrong, please correct me.


Edit, I would also like to know how to read the diagnostic (and how to get the diagnostic on my Motorola boxes from Comcast).
 

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You're taking the right route - you should leave your cable modem on as much of a direct line as possible (using the splitter), then make sure that you have a high quality splitter or amp if necessary for the video side. Cable amps, especially ones with modulators, have a tendancy to mess with your cable modem's signal, leading to internet service drops & downgraded service (lower speeds).


I'm not an expert, but the main things you want to look at when interpreting your cable statistics are the signal to noise ratio (higher is better) and power level. If your power level is too low or too high, or S/N ratio is too low, you'll have problems "locking" onto the signal from either your cable box or your cable modem.
 

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Discussion Starter · #6 ·

Quote:
Originally Posted by
/forum/post/12879040


Correct me if I am wrong, but since your HD box is a digital box, you are not going to get a better picture by upgrading the wires. With digital, you either get it or you don't.
[/QUOTE]



is this true??
 

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Quote:
Originally Posted by stateordie /forum/post/12889185


;12879040']Correct me if I am wrong, but since your HD box is a digital box, you are not going to get a better picture by upgrading the wires. With digital, you either get it or you don't.


is this true??[/quote]

Yes it is. Unlike analog digital works either 100% or it works 0%. There are no varying levels of working when it comes to digital.
 

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Discussion Starter · #8 ·

Quote:
Originally Posted by egnlsn /forum/post/12889461


Yes it is. Either it works 100% or it works 0%. There are no varying levels of working when it comes to digital.

no kidding... so if there is a weak connection between the outlet and the coax leading to the box - as long as im getting a picture, it doesn't matter that there is a bad connection, or bad signal/wire, etc?? ... its as good as its gonna get



if so, im confused on why other people have tried drop amps, etc and had success...
 

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Quote:
Originally Posted by stateordie /forum/post/12889489


no kidding... so if there is a weak connection between the outlet and the coax leading to the box - as long as im getting a picture, it doesn't matter that there is a bad connection, or bad signal/wire, etc?? ... its as good as its gonna get



if so, im confused on why other people have tried drop amps, etc and had success...

If there is either too little or too much signal there can be tiling (picture breaking up into little squares), but the pixels that make up the picture itself are either on or off -- no snowiness or fuzziness or any other such noise caused by an in-between state. Kind of like the burners in your furnace -- they are either on or off.
 

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Discussion Starter · #10 ·
interesting... cable tech came out tonight and checked the connection behind the wall plate, tightened it up (he said the installer put the barrel on backwards - not sure how that would matter
) and put a filter on the splitter, and the picture is noticably better than it was before. So the assumption that if you get a picture through the digital box - its as good as its gonna get seems to be incorrect...?
 

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Quote:
Originally Posted by stateordie /forum/post/12901209


interesting... cable tech came out tonight and checked the connection behind the wall plate, tightened it up (he said the installer put the barrel on backwards - not sure how that would matter
) and put a filter on the splitter, and the picture is noticably better than it was before. So the assumption that if you get a picture through the digital box - its as good as its gonna get seems to be incorrect...?

If the picture quality actually did change, it must be an analog channel that the before and after is being compared. The assumption that a digital signal either works or it doesn't is not an assumption -- that is just the way digital works.
 

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Discussion Starter · #12 ·

Quote:
Originally Posted by egnlsn /forum/post/12902663


If the picture quality actually did change, it must be an analog channel that the before and after is being compared. The assumption that a digital signal either works or it doesn't is not an assumption -- that is just the way digital works.

ahh... interesting - i appreciate the time and your responses... thanks for the help!
 

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Quote:
Originally Posted by stateordie /forum/post/12871567



Downstream:

Frequency 663000000 Hz

Signal to Noise Ratio 36 dB

Downstream Modulation QAM256

Network Access Control Object ON

Power Level 4 dBmV


Upstream:

Power Level 46 dBmV


Now, just as an experiment - i switched two of the cables so that my 2-way splitter now feeds my HDTV box and the 8-way, with the cable modem hooked to the 8-way. With this setup, i got the following:


Downstream:

Frequency 663000000 Hz

Signal to Noise Ratio 35 dB

Downstream Modulation QAM256

Network Access Control Object ON

Power Level -5 dBmV


Upstream:

Power Level 55 dBmV

I think you've gotten good advice on your PQ issues, but just for grins here is some info on the modem technical data you posted.

Downstream frequency refers to the channel that your CATV system uses for sending (downloading) data to your modem. "663000000 Hz" is 663 MHz which is in the middle of CATV standand channel 102. They use Quadrature Amplitude Modulation with 256 levels (QAM256) to send the data. For most CATV systems this is the same modulation standard used for both SD and HD digital television too.


You didn't mention upstream frequency, but it typically is in the CATV "return path" sub-band below channel 2, or somewhere between 6 and 54 MHz.

Power Level in dBmV is a measure of signal strength, in decibels relative to a reference level of 1 millivolt (1 /1000 of a volt). For downstream, usable numbers range from around -15 dBmV to +15 dBmV, with something in the 0 to +5 range being ideal. The lower -5dBmV number you got with the 8 way splitter is a little low but should make no difference to either your set top box for digital TV channels or the modem for data transfer. (Analog is another story...)


The Upstream Power Level refers how hard the modem has to work to transmit (upload) a signal back to the headend. Note that via the 8-way, it iwent from +46 to +55 dBmV, or an increase of about 9dB, pretty close to the expected extra 7 to 8 dB loss in a passive 8-way splitter over a 2-way.


The Signal to Noise Ratio is just that, the ratio of the desired signal to the undesired (noise), expressed in decibels and always a positive number. In the 30's is very typical, higher is better, but again with digital devices, operation will probably be OK until this number is very poor, maybe even single digits. Note that the receive S/N didn't change much even though the signal was 9 dB lower.


We can infer that your cable signal strength at the demarc (ground block on the side of the house) is at least +8 dBmV, which is very good to excellent, by adding the 2-way splitter loss of 3.5 dB to your +4 reading. Depending on the length of your in-house coax from the demarc to the first splitter, it may actually be a few dB higher. And since we are talking about +8 dBmV at ch 102, near the very top end of the CATV range, the low channel strength is probably a few dB higher than that, due to the greater loss of coax at higher frequencies.


Have your eyes glazed over yet??


Enjoy your TV.


Mike
 
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