digital cable and splitting in Cable users http://www.dslreports.com/forum/r4206348 en Sun, 08 Nov 2009 21:15:07 EDT Sun, 08 Nov 2009 21:15:07 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4496400 RFtoLitetoRF : Yes, 20-27dB CNR is too low. Consider this...FCC spec for analog carrier CNR is >43dB, so if digital carriers are set 8-10dB below the analog carriers at the headend, corresponding minimum digital CNR would be about 33dB. The margin of headroom here is about 5-8dB, so minimum digital CNR is about 25dB. Less than this and the BitErrorRate begins to climb. This then creates the "tiling" of the picture. If your at 25dB now, any fluctuations is signal strength or purity will surely affect your reception.
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A job worth doing is worth doing right!]]> http://www.dslreports.com/forum/remark,4496400 Sun, 22 Sep 2002 13:21:04 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4496079 BillRoland : Would an SNR of 20-27 be considered too low for a digital cable box? ]]> http://www.dslreports.com/forum/remark,4496079 Sun, 22 Sep 2002 12:33:51 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4335173 anon : Whatever the cable company doesn't want you to do is most likely the best way to do it.]]> http://www.dslreports.com/forum/remark,4335173 Thu, 05 Sep 2002 00:20:35 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4256828 all_in_1 :
said by Raydr:
Troubleshooting can really be a pain without a meter.
Like trying to find the bathroom in the dark.
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You need to set a time when you can be there when the tech arrives so you can show him, and see what he shows for levels at your sets.
FCC minimums for S/N is >43dbmv.
If your S/N is that low (20-30) an amp will not improve it.
IF you feel that you need to buy an amp, please buy one from Charter. At least you will get a quality product.
[text was edited by author 2002-08-27 23:22:14]
]]> http://www.dslreports.com/forum/remark,4256828 Tue, 27 Aug 2002 23:13:43 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4249699 gelbelt : I'm tempted to dig up some 50 to 75 ohm pads and use the network and spectrum analyzers at work to do some testing. That way I could check out my amp and splitters, but I'd have to borrow the SA to check the signal at my house.

If I do the amp myself, is there anything that could come back to bite me in the ass later? Even if the cable company game me an amp inside, I could still have a problem if they ever do fix the signal level on the street. I'll just have to keep an eye on the levels. Really, it looks like I have enough SNR coming into the house to split and amplify. What SNR do techs consider good/bad? With the 14 dB amp, then a splitter going to the set-top box and VCR, I'm seeing -7 dBmV at each unit and SNR in the 20-30 dB range. The picture quality is good on the analog channels, and the digital tuner seems happy.]]> http://www.dslreports.com/forum/remark,4249699 Tue, 27 Aug 2002 10:24:12 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4248794 Raydr : Sorry, I forgot that service calls aren't set up for time frames. My bad. Heheheeh

Anyway, the cable box isn't going to help much with diagnostics, unless you carry it and a TV to each point where you want to test. If you have a cable modem...you probably want to use it instead. I go over this in my FAQ.

Troubleshooting can really be a pain without a meter.
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~Check out my Cable Modem/Wiring Issues FAQ~ Please do not reuse my screenshots without asking! :)]]> http://www.dslreports.com/forum/remark,4248794 Tue, 27 Aug 2002 06:56:13 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4246823 gelbelt : It looks like I have two choices:

1) Call the cable company, set up an appointment, wait for the tech, use all of my patience explaining the problem to him and still not getting it fixed the way I want it, and ending up with an amp going into the set-top box that I don't want and will end up moving anyway. The problem is obviously that there isn't enough signal at the street or else I wouldn't have -10 dBmV at the ground block. He wouldn't acknowledge that and really didn't know what he was talking about. He kept on about the upstream being the problem even though I told him the downstream was -18 dBmV at the set-top box but the upstream there was around 35 dBmV. This indicates the set-top box and modem aren't having to crank up their gains to reach the other end.

2) Do it my way, and live with the poor signal level coming into the house, hoping I have enough SNR and good enough components to add gain myself. I'm thinking about moving all of the cable pulls inside the garage instead of outside, then adding an amp and splitters there along with the new pulls of RG-6 quad shield.

As I said, the Radio Shack amp was just an experiment. I will say that it works well and adds a good amount of gain without badly degrading the SNR. If I decide to do the work myself I'll be returning the Radio Shack amp and getting a more professional one.

By the way, when I called the cable company I was told they'd have a technician out sometime in the next few days, "probably before Monday." Nobody could reasonably expect me to sit at home for the entire weekend waiting on a cable tech. If he was ticked off right from the start he shouldn't be working for Time Warner. Would you rather me have not left a note, so he'd be left with no aids when he got to the house?

Thanks for your help along the way. I did find a tutorial on Scientific Atlanta's web site about using the diagnostic pages, but it mainly talks about the initial setup. It doesn't say anything about troubleshooting signal problems.]]> http://www.dslreports.com/forum/remark,4246823 Mon, 26 Aug 2002 23:19:15 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4243461 Raydr : NO. YOU HAVE JUST DONE SOMETHING THAT ALL CABLE TECHS HATE. TAKE THE RS AMP BACK! NOW!!! GO!!

Okay, you back? Those things are pieces of crap, and you should just go with the one the cable company gives you. Just make sure you're home next time. A cable tech isn't going to listen to a customer over the phone. When you're there, you can actually show him.

P.S.: Sorry, but leaving a note for the cable guy to call you is pretty annoying too. OUR logic is this: We're using up our OWN personal cell phone minutes to talk to a person who didn't bother to wait at home for us. He probably wasn't very compliant because he was ticked off right from the start. :)
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~Check out my Cable Modem/Wiring Issues FAQ~ Please do not reuse my screenshots without asking! :)]]> http://www.dslreports.com/forum/remark,4243461 Mon, 26 Aug 2002 18:28:01 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4236319 gelbelt : Well, the cable tech came out today. I wasn't home, but he saw my note and called me on my cell phone. He said the level at the ground block is OK or marginal. He kept saying the upstream was the problem and wouldn't listen to me about the signal level being too low coming into the house. He did offer to put on an amp, which doesn't make sense since he said the upstream was the problem. He didn't want to install it without me being there, so I'm supposed to call back and setup another appointment.

So, I picked up a bi-directional amp from Radio Shack just to experiment. Without the amp I'm still seing -10 dBmV for 74 MHz and -18 dBmV for digital channels up around 100. With the amp just before the set-top box I can get more than enough level.

Is there anywhere I can get more info on the 3100 diagnostic page? I'm wondering about things like FDC, RDC, etc. just to know what I'm looking at.

Thanks,
Adam]]> http://www.dslreports.com/forum/remark,4236319 Sun, 25 Aug 2002 22:50:06 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4219623 gelbelt : Where's good to buy parts? Radio Shack? Lowe's? PartsExpress.com? I saw the link to accessorywarehouse.com in the FAQ but am wondering about the others. I need a crimper, cable, connectors, and eventually splitters and maybe an amp.

Thanks,
Adam]]> http://www.dslreports.com/forum/remark,4219623 Fri, 23 Aug 2002 21:29:27 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4210295 gelbelt : Well, thanks for the advice. I guess I have to do battle with customer service now. I called a few days ago and was told things like "now, I'm not the one to be asking this" and "if you want to add TV's, the best thing is just to have a tech come and install them for you at $35 per outlet." Since I'm going to have them come out anyway, will I need a filter for other outlets?

Thanks,
Adam]]> http://www.dslreports.com/forum/remark,4210295 Thu, 22 Aug 2002 22:21:03 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4208689 Raydr : and FYI, you want to have between -7 and +12 at the outlets. Shoot for a -7 to 0 for the cable modem outlet first, and worry about the digital box after. Don't amp this line, because it's an outside problem. If they happen to fix it, and you keep the amp on, you'll end up with more problems because of too much signal.

The SNR of 23 or so is pretty bad, it means you have a lot of noise and ingress on the line. I'm guessing you probably have a cut or something like that somewhere outside. You did check the ground block, right?

See my faq for more info:

»Cable Modems and Wiring Issues
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~Check out my Cable Modem/Wiring Issues FAQ~ Please do not reuse my screenshots without asking! :)]]> http://www.dslreports.com/forum/remark,4208689 Thu, 22 Aug 2002 19:55:10 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4208652 Raydr : -10 at the ground block is horrible. Call the cable company and tell them; that's THEIR problem.]]> http://www.dslreports.com/forum/remark,4208652 Thu, 22 Aug 2002 19:52:02 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4208389 gelbelt : I got the splitter loss a little low. I'd end up with about -9 dBmV at the cable modem and set top box, then -15 or so at the other devices. I guess I should get an amp with more like 20 dB of gain since I'll probably be adding more TV's later. Do you think I have sufficient SNR coming off the street (around 30 dB at -10 dBmV level)?

Adam]]> http://www.dslreports.com/forum/remark,4208389 Thu, 22 Aug 2002 19:27:09 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4208319 gelbelt : Thanks for the reply. I'm really glad to know that the set top box has a diagnostic mode. I have an Explorer 3100. It reports -18 dBmV level and 23-27 dB SNR. That's for digital channel 101. The current FDC of 74 MHz has a level of -10 dBmV and approximately the same SNR. This is with a three-way splitter on the side of the house - one to the cable modem, one to the set top box, and one to the VCR.

Before I saw your note I carried the cable modem around and checked levels. It reported -17.4 dBmV on the outlets and -10 dBmV outside before the splitter. The SNR was in the 25-30 dB range.

Do you think I could get the cable company to do anything? The tech was rushed when he did the installation, and I didn't see if he checked levels. If he had -10 dBmV at the house and connected two outlets, with the splitter and cable loss the level at each outlet would be just above -15 dBmV.

Perhaps I should amplify the signal coming into the house since it is low to begin with. If I add 10 dB of gain, I'm up to 0 dBmV. From there I could do a three-way split, giving the cable modem and set top box around -5 dBmV each. Then if I split the last output of the three-way splitter, with a four-way splitter, I could have around -14 dBmV at each the VCR and three analog TV's.

Thanks again for your help,
Adam]]> http://www.dslreports.com/forum/remark,4208319 Thu, 22 Aug 2002 19:19:49 EDT Re: digital cable and splitting http://www.dslreports.com/forum/remark,4206441 Raydr : What type of digital box do you have? Explorer 2000 or higher?

If so, hold down the middle button (in the middle of the 4 other navigation buttons) until the "message" light flashes, and then press "Info".

Down at the bottom you'll have a couple of signal levels. List them here.

Post your cable modem signal levels as well.
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~Check out my Cable Modem/Wiring Issues FAQ~ Please do not reuse my screenshots without asking! :)]]> http://www.dslreports.com/forum/remark,4206441 Thu, 22 Aug 2002 16:12:36 EDT digital cable and splitting http://www.dslreports.com/forum/remark,4206348 gelbelt : Short question: Can I rely on my cable modem's reported downstream signal strength to determine if I need an amplifier for TV in my house?

I just moved into a new house and had cable TV installed. I only had the tech connect two of the seven pulls into the house, but in the coming weeks I'll want to activate additional outlets. I have to pull off the siding to bring cable into a room that doesn't have cable now, but that's another issue...

The cable comes off the street and goes into a two-way splitter. One leg goes straight to the cable modem (Toshiba PCX2500) and the other leg goes to my living room TV's digital cable set top box (Scientific Atlanta Explorer 3100). The cable modem works fine, and the digital cable works OK until I attempt additional splits. I'd like to split the living room cable so I can record on a VCR while watching another channel on the set top box. I'd also like to hook up another TV for football season. If I attempt a split in the living room, the digital cable craps out. I've managed to replace the two-way splitter on the side of the house with a three-way splitter that claims an equal -5.5 dB split among the three outputs. There are actually two cables pulled into the living room, so I've been able to use the extra pull for the VCR. The digital cable works OK now, but it still seems to loose signal briefly every so often. It seems I'm just on the bottom edge of the set top box's tolerance, so -7 dB total is too much but -5.5 dB is OK. I'm going to use the cable modem to measure signal strength in the living room to see what the digital set top box is getting.

I eventually want to move the cable modem into the study, which is why I need to take off the siding for another cable pull. I'll actually want the cable modem and a TV in the study, so I may pull two cables into that room. Within a few months I'll want to have three TV's in the house, the cable modem, and the VCR. I'm thinking of a two-way splitter on the side of the house, one leg going to the cable modem and the other going to a four-way amplified splitter. I may add even more TV's later, so I'm getting into quite a distribution problem.

Oh, one more thing - the tech didn't install a filter, I assume because the digital set top box needs the low frequency return path for PPV and what-not. Should I aim to have filtering on all of the non-digital TVs?

One last thing - if the signal strength is low, which amplifiers and splitters should I use? I know I need a bi-directional amp if the cable modem and set top box will be behind the amplifier.

Thanks,
Adam]]> http://www.dslreports.com/forum/remark,4206348 Thu, 22 Aug 2002 16:04:13 EDT