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Old 06-15-2014, 08:41 AM   #1
drawz
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Pixelation on TiVo when uploading over cable modem?

I'm having a bit of an unusual issue. I noticed seemingly random pixelation on FoodHD (854 on Comcast Boston/Brookline) for several months and finally investigated. Other channels seem fine.

From DVR diag:
  • Signal level is 98-99% with SNR 39dB
  • Some RS uncorrected errors on this channel only (241149 in 8 hours)
  • Lots of RS corrected on this channel only (3004420 in 8 hours)

Equipment:
  • Roamio Pro
  • Motorola SB6121 cable modem
  • 2-way splitter to cable modem/Roamio Pro

The interesting part is that running a speedtest causes the uncorrected errors to sky rocket during the upload phase of the test. This also instantly causes terrible pixelation. I get 3260 uncorrected and 4986 corrected errors during a single speedtest, all uncorrected and the vast majority (99%) of corrected errors occurring during upload. I suspect that the seemingly random pixelation I've been getting coincides with random upload bursts from the various computers and other internet connected devices in the house.

Even without the speedtest involved, I get some uncorrected errors on this channel, but 0 on others that I checked. Doesn't seem to matter which tuner is used. I did get random pixelation on the same channel with my old Premiere XL4, but it seemed much less common. I never tested the upload thing since I just stumbled upon that last night.

Any ideas what might be going on here? Anything else I should check?

Last edited by drawz : 06-15-2014 at 09:00 AM.
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Old 06-15-2014, 05:53 PM   #2
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You might need to add a 5-10 dB attenuator to your cable to bring the SNR down to at least 37dB. Cable source is a bit too strong.
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Old 06-15-2014, 11:29 PM   #3
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Any idea why it would only affect one channel (as far as I can tell)? Or why uploading over the cable modem would make it worse?
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Old 06-15-2014, 11:43 PM   #4
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Any idea why it would only affect one channel (as far as I can tell)? Or why uploading over the cable modem would make it worse?
That depends on the frequency the problem channel is operating on.

Check DVR Diagnostics to find it. Then check what frequencies your cable modem is using. You may find an overlap, or that the frequencies are close to each other.

If not, and a TA is in use, there may be some overlap in the frequencies the TA communicates on.

If one device is pushing too strongly upstream, or one is receiving too high of a signal, it can cause an overpowering interference.

Often, devices will boost power as they are pushed to operate at higher throughput, as opposed to being idle, or operating at low throughput.
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Old 06-16-2014, 12:49 AM   #5
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It could also be a harmonic of the modem's frequency effecting your TV channel's freq.
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Old 06-16-2014, 12:57 AM   #6
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It could also be a harmonic of the modem's frequency effecting your TV channel's freq.
Could be any number of factors, really.

This is a situation where one would want to make sure all unused coax ports on splitters are terminated, and terminators are placed at every unused wall-plate.

That's just best practices, anyway. In the digital age, there shouldn't be any ports or wallplate barrels without a terminator, if not in-use.

The list of possibilities is a long one. This is a good starting point. Unterminated splitter ports allow ingress/egress, and signal reflection (bad). This is compounded when there's a run of coax with an open end.
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Old 06-16-2014, 11:38 PM   #7
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Thanks everyone! I'll try the terminators and/or attenuators first.
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Old 07-31-2014, 06:46 PM   #8
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Finally got around to troubleshooting this some more.

Tried a 6dB attenuator from Smarthome, which knocks down the signal strength to 87-90% and SNR to 35-36dB on the effected channels. Unfortunately, I still get tons of pixelation when running the upload portion of an internet speed test, along with tons of RS uncorrected and some RS corrected errors. The splitter I'm using is from the cable company and appears to be high quality.

Haven't tried the terminators yet, but I do also have those and will try them tonight hopefully.

Any other ideas?

*edit* I now get 75k uncorrected errors with one speedtest run, all on the upload side, although this is in the setting of having my QoS off on my router. With QoS on, slowing down my upload speed by about 5%, I get fewer errors, but still an unwatchable picture.

Last edited by drawz : 07-31-2014 at 07:00 PM.
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Old 08-12-2014, 03:05 PM   #9
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Have you had any luck getting this fixed?
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Old 08-12-2014, 03:18 PM   #10
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The splitter I'm using is from the cable company and appears to be high quality.

Haven't tried the terminators yet, but I do also have those and will try them tonight hopefully.

Any other ideas?

*edit* I now get 75k uncorrected errors with one speedtest run, all on the upload side, although this is in the setting of having my QoS off on my router. With QoS on, slowing down my upload speed by about 5%, I get fewer errors, but still an unwatchable picture.
It seems like you might have a bad splitter. Are you somehow the 1% that uses a single splitter for everything? That rarely works out. I haven't re-read the whole thread to try and extrapolate how everything is hooked-up.

Try the terminators first. Then I suggest it might be time to start replacing splitters and coax, until you find the problem.

It almost sounds like the port isolation of a splitter somewhere is too low, or it could be bad/damaged coax. Are you certain there aren't any splitters inside walls, or in places you haven't looked? Have you traced-out where all coax comes and goes?
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Old 08-12-2014, 11:08 PM   #11
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Wow, I just came to give an update that I thought was brilliant, but nooneuknow beat me to it by a few hours! I think the splitter was a big contributor as it improved SIGNIFICANTLY when I swapped it. I still get pixelation and image break up if I turn off my router QoS, but it looks fine with QoS on. The random pixelation also seems less frequent, but too early to say for sure. I did not add the terminators yet.

For clarification - the coax comes into my condo building somewhere unknown to me, so I'm not quite sure what is going on outside. In my unit, there is a 6-way splitter supplying all the rooms (two drops to most rooms). My TiVo and cable modem are connected via a single 2-way splitter from Comcast and they are the only devices in use in my unit. There is now a 6dB attenuator on the TiVo side of the split. I haven't tried taking the attenuator back out.

I suppose I should terminate the unused ports either at the 6-way splitter or at the open ports in each room. My next move was going to be trying new coax cables in case of a broken shield or bad connector. These were also supplied by Comcast and cut to length by the tech, so I could easily see them failing.

FWIW - this exact set up worked just fine with my TiVo Elite, so the Roamio is more sensitive for whatever reason.

Thank you all for your help! If I get time to play with it any more, I'll add anything useful that I discover.
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Old 08-13-2014, 02:17 AM   #12
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Splitter port-isolation (high=good) is key to stopping crosstalk between OUT ports on a splitter. Used in conjunction with terminators, it can keep things running smoothly. Regardless of how something else worked before, unless the interference is coming in over the network, it seems like your Cable Modem and Cable TV signals need better isolation. You can create more isolation between the two, by using more splitters. You can also attenuate in a much better way, if you use splitters and terminators to do so. This is how Cox does it in my 1GHz market. They no longer install, or allow attenuators. Any attenuation needed must be done by using splitters with excessive OUT ports, and/or daisy-chaining more splitters in-line. I prefer to daisy-chain most of the time, and keep my cable modem as many splitters away from my TiVo, as is possible. When doing this, terminators are NOT optional.

It also sounds like it's possible your TiVo has a defective internal filter for 5-54Mhz frequencies, which cable modems, tuning adapters, and EMTAs broadcast at high power on, to push the upstream all the way back to the cable plant. Here's the fix for that: http://www.wiredathome.com/cables-an...h-pass-filter/
Be warned, the only place this can be used is screwed directly to the port on the back of the TiVo. I used to have to use these with TiVo HDs, due to an issue like yours.

Some comments on splitters:

I recommend 1GHz. If you can get 1.2GHz for a little more, get that. 1000MHz=1GHz. Some splitters will say 5-1002MHz. Those are essentially 1GHz splitters trying to stand-out as better. Make sure it says "digital" somewhere on the splitter itself (not just the box it is in).

Do not get higher than 1.2GHz. Do not pay extra for something that says "MoCA-enabled" or "MoCA-enhanced", etc. It's the same deal as with HDMI cables that cost more, for the brand and enhancements that are BS.

The one real problem is: I can't buy any splitters that won't have problems like you do, from retail stores, no matter what they cost. I either have to get one from a cableco van, the local Cox store, or mail-order them. Nothing Wal-mart, or the likes-of is worth the packaging it's in. Home Depot might have some good ones, if you are lucky.
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Old 08-14-2014, 09:53 PM   #13
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Thanks for the additional info. I happened to have another one from Comcast that seemed to solve the problem. I still have the 6dB attenuator inline with reasonable signal levels. If you go back to my first post in this thread, you'll see the signal was a bit strong to start. I don't think I'm going to mess with it much more at this point since it's working ok, but I'll keep your other tips in mind if issues crop up again.

*edit* the product you linked is very interesting. going to bookmark that one...
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Old 08-14-2014, 11:09 PM   #14
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You might want to keep a eye on the RS corrected and corrected errors. I get less than 100 a day. I had to get the cables in my house perfect to make my original Tivo HD work because of a bug in the internal tunner firmware that did not terminate the line correctly inside the Tivo years ago. That bug was eventually fixed by tivo but taking the time to correct the cable issues means I almost never have internet or TV issues.

You might want to log into your cable mode at 192.168.100.1 and look at the signal tab. The weaker or more noisy signal the modem gets the louder it has to transmit to get back to the mother ship increasing the noise on the line. Dslreports has a good section on what the numbers should be.

In my case I just had to get comcast to replace all the old crimp connectors on my cables with the newer O-ring sealed two part weather tight connectors and removed all the old unneeded taps in my 25 year old house.

Comcast will not care about the errors on the cablecard but you should be able to get them out to fix errors on the cable modem if you have slow internet response and you say the right things.

The quality of internet service is a big deal for me because I work from home. My wife also is quick to point out any issue.
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Old 08-21-2014, 11:12 PM   #15
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So I moved some things around to clean behind my TV and the pixelation is back! Makes me suspicious of bad cables or a bad crimp that was a little positional. Same channels, same cable modem upload issue.
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Old 08-22-2014, 01:38 AM   #16
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So I moved some things around to clean behind my TV and the pixelation is back! Makes me suspicious of bad cables or a bad crimp that was a little positional. Same channels, same cable modem upload issue.
Time to get some new RG-6 "patch" cables. It's not easy (for the typical person) to put new ends on, nor are the tools to strip and secure the ends, cheap (the ones worth using). I have all the tools, know what I'm doing, and still would rather replace the "patch" coax cable, than spend the time to put new ends on one. The ends aren't cheap, either, unless you buy in bulk.
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Old 08-22-2014, 10:11 AM   #17
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I'm on Comcast up in Southern NH. I can tell you that 854 is one of the channels that I've had issues with in the past (along with channels like 832, 872, 823), both on Tivo's and Comcast DVRs. It's something about how Comcast sends the signals for these that I think tends to have them had more issues.

You can certainly try to reduce your SNR if you want, but I know that the Plus/Pro Roamios boost the signal compared to the Basic. I had nothing but problems when I tried reducing my levels (right now I'm around 41 SNR), so I left it alone. Initially when I was attenuating my signal, it's the above channels that consistently had signal issues where none of the other channels did.

In fact, back when I had a Comcast DVR, at one point I would get all the channels except for the ones above where I would get no signal. Comcast tracked it down to a bad coax connector. So I guess I'm saying I think a channel like 854 is more prone to have issues if you have coax/line problems.

I just ran a speedtest while viewing 854 and didn't notice any issues here, so you might want to replace cables to see.

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Old 08-22-2014, 10:50 AM   #18
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What could be of more use to know, is what frequencies the channels you list are carried on, and if any of they share the same frequency. It's also great to know what frequencies any cable modems, TAs, or EMTAs are operating on.

I avoid speaking about channel numbers, and try to focus on what frequency range they are in, if I'm going to bring up problem channels.

I get that a common provider might use the same channel numbers in all markets. Some might even carry the same channels on the same frequencies. It's just not that simple, most of the time.

It's also helpful for newcomers that might find a thread, and think a mention of channel 1018 and/or or TNTHD, will apply the same with them. The only time network channels might help others, is if people in multiple markets are having issues with TNTHD, none on the same frequency, but all seeing a problem. Then, it tends to point to that network channel.
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Old 08-22-2014, 10:46 PM   #19
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Thanks for the tips guys. Any advice on where to get some decent, but reasonably priced, RG6 patch cables? Can I go to my local Comcast office and get some freebies?

I'll look up and post the frequencies for the effected channels later this weekend.
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Old 08-23-2014, 01:11 AM   #20
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Thanks for the tips guys. Any advice on where to get some decent, but reasonably priced, RG6 patch cables? Can I go to my local Comcast office and get some freebies?

I'll look up and post the frequencies for the effected channels later this weekend.
The local Radio Shack, Best Buy, any electronics store, even Walmart or Target.
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Old 08-23-2014, 03:13 AM   #21
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Just beware of false cables, that have RG-6 ends, but the cable is actually RG-59 (the thinner, unacceptable, predecessor to RG-6).

If the cable jacket does not specify RG-6, or has no specification, don't trust that the packaging is being truthful.

Even the Cisco TAs come with a RG-59 patch cable (which is just pure cheapness stupidity). What tends to happen is that any coax connector that has had RG-6 inserted (especially inserted many times), will be unable to grip the thinner RG-59, and causes a bad connection. While RG-59 is nice for being so flexible, it's shielding is terrible, it loses signal much more, and many "fake" RG-6 ends are usually just slipped over the RG-59 conductor, without any assurance there is a good connection between the two.

Also, beware of the slip-on coax, which slides over the threads. It's great for troubleshooting, where you want to save the time of screwing/unscrewing, but should never be left in use. Even though Cox forbids that customers use them, their techs use adapter ends with the slip-ons for their meters/analyzers, and when they are substituting patch cables, while looking for a problem. They don't use cables that have them on the ends. They use good cables that they screw such adapters onto the ends of. This makes sense, given the time it saves over the course of a day. Some techs still eschew the use of them, and would rather get carpal-tunnel, than even test with slide-on ends. I use them for tamper-proof terminators, like the cableco uses, when I'm changing things around, and want to quickly/easily temporarily terminate an open port. When I'm done, I use the special tool to screw them on. Store-bought terminators are not tamper-proof (but aren't free, like those that "fell off" a cable truck).

P.S. If it says "Radio Shack" on it, be prepared for long sighs if you ever have a cable tech out. In my experience, not only is most Radio Shack stuff poor-quality and over-priced, the cableco tends to blame all problems on any of it found in your home.
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Old 08-24-2014, 06:12 PM   #22
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The local Radio Shack, Best Buy, any electronics store, even Walmart or Target.
My experience with cables from all of those places is that they are overpriced and only sometimes decent quality. Maybe monoprice?
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Old 08-25-2014, 01:09 AM   #23
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My experience with cables from all of those places is that they are overpriced and only sometimes decent quality. Maybe monoprice?
I would have said the same thing. Except, monoprice will charge you more for shipping, than what you pay for even multiple cables. Unless somebody has enough they need from monoprice, and keeps adding to their cart, until the shipping cost bumps-up a level, and then takes one item out, the shipping is enough to discourage many, including me. It's unfortunate, since they are the best source for almost all cables, best quality, at the best prices (shipping not factored in).
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Old 08-25-2014, 04:35 PM   #24
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Monoprice is having a special with free shipping for cables, good through 09/08/14. No special codes required.

At least that's what my email promo sub tells me. Knowing monoprice, it's probably limited to certain cables.
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Old 08-31-2014, 12:22 AM   #25
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Thanks for the heads up, will try monoprice and hopefully get free shipping.

I moved things around some more so that none of the RG6 cables are crossing each other or are bent significantly. This has helped significantly, but not completely eliminated the problem. Limiting upload speeds by QoS still is essential (only reduced by about 5%).

For those wondering, the channels in question and their frequencies:
842 (CNN) - 67750 kHz (QAM 256, 97% signal, 39dB SNR)
846 (UHD) - 85750 kHz (QAM 64, 94% signal, 37dB SNR)
854 (FoodHD) - 85750 kHz (QAM 64, 94% signal, 37dB SNR)

Interesting that two are at the same frequency, but not all 3. I wish there were an easy way to find channels on the same frequency.

Signal and SNR are with a 6dB attenuator inline. Using a 2-way splitter provided by Comcast (replaced once already, which I thought did the trick but then didn't after moving things around).
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Old 08-31-2014, 12:49 AM   #26
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Thanks for the heads up, will try monoprice and hopefully get free shipping.

I moved things around some more so that none of the RG6 cables are crossing each other or are bent significantly. This has helped significantly, but not completely eliminated the problem. Limiting upload speeds by QoS still is essential (only reduced by about 5%).

For those wondering, the channels in question and their frequencies:
842 (CNN) - 67750 kHz (QAM 256, 97% signal, 39dB SNR)
846 (UHD) - 85750 kHz (QAM 64, 94% signal, 37dB SNR)
854 (FoodHD) - 85750 kHz (QAM 64, 94% signal, 37dB SNR)

Interesting that two are at the same frequency, but not all 3. I wish there were an easy way to find channels on the same frequency.

Signal and SNR are with a 6dB attenuator inline. Using a 2-way splitter provided by Comcast (replaced once already, which I thought did the trick but then didn't after moving things around).
Those are just above the band that this product http://www.wiredathome.com/cables-an...h-pass-filter/, I described in an earlier post, would filter out for you.

TiVo would tell you that your SNR is too high, and to attenuate more. I'd almost bet that daisy-chaining some splitters, or using one with excess ports, rather than using attenuators, would make a world of difference. But, you clearly seem to have an issue with the cabling you are using. So, you need to start replacing cable, or keep trying band-aid workarounds.

The thing that I think is missing, is a post showing what your cable modem data shows for frequencies it is on, strength, and SNR at the modem, with extra special attention to what the upstream power shows, while doing what causes the problem.

Since you need attenuation, the more splitters you put in, the better the port isolation, plus you get attenuated. But, if you don't use terminators on unused splitter ports, you might make things worse.

This problem seems like it should have been solved a week ago. I recall one person having MoCA issues pulled all his hair out, only to find it was a bad "barrel" connector (like what goes in a wall plate, allowing in-wall cable to screw to the inner nipple, and providing an outer nipple to connect the jumper coax to). If you have any coax that has been bent at sharp angles, it needs to be taken-out, or have the bent part cut-out, and a new connector installed on it. Coax, once bent sharply, will be forever damaged internally, at the site of the bend.
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Old 08-31-2014, 01:41 AM   #27
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Here is my cable modem signal page right after a speedtest (it actually wouldn't load when uploading at full speed, which is when the signal breakup occurs).

http://imgur.com/KNAplbm

Totally agree it should have been solved earlier, but I haven't been home enough lately to fiddle with it. Sounds like starting with new cables and possibly adding more splitters (with terminators) is the first thing to do.

The thing that's weird with all of this is that it worked just fine with my Elite. It does seem like the Roamio is more sensitive from what I'm reading around here.

Thanks again for your help!! I know we don't say that often enough around here!
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Old 08-31-2014, 04:16 AM   #28
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Here is my cable modem signal page right after a speedtest (it actually wouldn't load when uploading at full speed, which is when the signal breakup occurs).

http://imgur.com/KNAplbm

Totally agree it should have been solved earlier, but I haven't been home enough lately to fiddle with it. Sounds like starting with new cables and possibly adding more splitters (with terminators) is the first thing to do.

The thing that's weird with all of this is that it worked just fine with my Elite. It does seem like the Roamio is more sensitive from what I'm reading around here.

Thanks again for your help!! I know we don't say that often enough around here!
I'm not liking your modem readings, too many errors (unless it's been ages since being rebooted). Also, the modem is on the low side (over-attenuated). Can you change the cables so the TiVo and Cable modem are on opposite ports (reversed), reboot things, and see where levels are at? Realistically, unless the act of reconfiguring coax connections corrects a bad connection (which would explain your temporary reprieve, when you swapped splitters), you should wind up golden, reversing the two around, and might not need attenuation on the TiVo. But, I still think you have a bad connector to coax connection, bad cable, or some combination of this.

0.0dB is a perfect signal, and -8dB is on the edge of too low. The modem may be pushing the upstream too hard (too much power), when the problem is happening.

The thing that stands out still is the other TiVo was doing OK. If I had your problem I'd put that filter I mentioned on the tivo coax nipple, as a diagnostic step.

Since you have two splitters, if you have some more coax cables, you could put one splitter as the first split, only connect the modem to it, connect the other splitter to the other OUT port, then connect the TiVo to one of the ports on the second.

But, wait, I keep re-reading your older posts, and you talk about a six-way splitter at the point of entry. Your cable modem should have a direct run to that splitter. It always works best if the cable modem is on the very first splitter, with no more splitters on the way to the modem. Then, if the TiVo SNR is above 36 and the signal at or near 100, add splitters daisy-chained to bring it down. The TiVo only needs a signal of >70, ~80-90 is good, and should not be pegged at 100.

That first six-way sounds like something that should have been the first suspect in all this. If it's under-rated, poor quality, or has been around a while, and has developed issues, nothing else you do is going to band-aid that splitter. If it's been around with open ports, it's probably full of dust, dirt, moisture, and maybe corroded inside.

If you can get a free truck-roll from your cableco, for a signal test, they'll likely wind up replacing that 6-way, and putting on a bunch of new ends. Your cableco should never leave open ports on anything they install (or even anything they touch).

Really it should break down like this:

1. Have the signal test performed, and make sure they test at that first splitter.
2. Be sure the first splitter is good, and unused ports terminated.
3. Get the cable modem working at the right levels with a home-run to that first splitter.
4. Deal with another run to use for the TiVo, if possible.
5. If moving cables behind things causes any changes, replace those cables.

I've recently done other backwards troubleshooting like I've done here. The people didn't want to call the cableco out, and I wasted a lot of time, when it turns out the problem was a defective tuning adapter, which was not the person's responsibility to deal with. New TA provided, all was well again. If I'd pressed harder to just call them out, time and money would have been saved.

No matter how bad your local provider might be, some things are their responsibility, not yours, and they often will replace the ends on your coax as routine procedure, unless you get a complete slacker of a tech.
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Old 08-31-2014, 10:17 AM   #29
drawz
Registered User
 
Join Date: Aug 2011
Posts: 25
Thanks for the advice. Any tips on convincing Comcast to come out and do a *free* signal check? Will the pixelation be enough or will they point at the TiVo and cable modem as being customer-owned equipment?

FWIW - uptime on the cable modem is about 12 days, which is the time since I cleaned behind the TV and swapped the splitter.

*edit* - just looked at the primary splitter - it is actually 3-way and of high quality. No open ports.

Last edited by drawz : 08-31-2014 at 10:45 AM.
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Old 08-31-2014, 03:57 PM   #30
DeltaOne
Mount Airy, MD
 
Join Date: Sep 2013
Posts: 184
Quote:
Originally Posted by drawz View Post
Any tips on convincing Comcast to come out and do a *free* signal check?
Call in a trouble ticket saying you lost TV on every set in your house. Nada, zip - no TV works.

When the tech arrives tell him the TV signal is intermittent and you suspect low signal level. If you're polite and get a good tech -- he'll check the level coming in to your house and at each set.
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