# SNR presence with not plugged it



## dlongnecker (Dec 31, 2006)

I've been trying to troubleshoot the problem with my new Roamio not getting authorized for about 3 weeks. While both Tivo and Comcast are trying to be helpful, its not going anywhere. (I'm getting all channels but the premium ones and VOD freezes.).

Tivo claims my SNR is too high. Its at the 42 level. Tried putting attenuators in place, to get it down to 36, but then I lose my internet connection.

For grins, I wanted to see what my SNR on the TIvo is when absolutely nothing is plugged into it but the HDMI cable and Power. Right now, SNR is 19. Switched cable cards, it is 19. This is with nothing plugged into the coax. All other electronics, except for the TV turned off.

Does it seem unusual that I start out with a 19 SNR level with nothing plugged in?


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## kbmb (Jun 22, 2004)

Where are you putting the attenuators and what is losing internet....the Tivo or the whole network?

-Kevin


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## StevesWeb (Dec 26, 2008)

No, when the input to an amplifier is open it is going to sit there amplifying noise.

I am deeply skeptical of claims that a superior signal to noise ratio will cause a TV tuner to malfunction. I believe what is actually happening in some cases is that the signal level is too high. Adding splitters reduces signal level. Adding more noise to a signal is not an improvement, whether the data being modulated is analog or digital.

So, when a TiVo tech says the SNR is too good I consider an indication of his ignorance of what the term means and how it relates to TV tuner performance. Maybe the peak to peak signal level is too high.

It will often be the case that strong signals also have high (desirable) signal to noise ratios, this may be how this false correlation got started.

Ignore the SNR, it is a red herring.


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## CrispyCritter (Feb 28, 2001)

StevesWeb said:


> So, when a TiVo tech says the SNR is too good I consider an indication of his ignorance of what the term means and how it relates to TV tuner performance. Maybe the peak to peak signal level is too high.
> 
> Ignore the SNR, it is a red herring.


I agree with most of your analysis, but you left out an important adjective phrase. The TiVo tech is saying the SNR *as reported on the TiVo* is too good. We don't know that the TiVo SNR is a true signal-to-noise-ratio and I strongly suspect it isn't. It's some mixed up number that has a strong signal strength component.

There have been many folks in this forum that have been helped by reducing the signal strength (either attenuators or getting the cable company to fix it) after noticing the the SNR as reported on the TiVo is that high. In practice it seems to be a quite valuable diagnostic number, even if it shouldn't be called "SNR".


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## shamilian (Mar 27, 2003)

Just use the Signal Strength value.

Get it in the mid to high 90s and that should be good.
(over 100% and your signal may be clipped)

The SNR value is not useful and no one knows how it is computed.


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## StevesWeb (Dec 26, 2008)

CrispyCritter said:


> I agree with most of your analysis, but you left out an important adjective phrase. The TiVo tech is saying the SNR *as reported on the TiVo* is too good.
> 
> In practice it seems to be a quite valuable diagnostic number, even if it shouldn't be called "SNR".


Good point. It does seem what is really helping in such cases is reducing signal level. It certainly is possible to overdrive the input on a tuner.


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## dtivouser (Feb 10, 2004)

The Tivo rep had me unplug the coax from my Romaio. When it still showed 15db, he said that's a defect and RMA'ed my Tivo. The replacement fixed almost all of the problems I was having. 

Call Tivo and tell them about this.


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## lgnad (Feb 14, 2013)

Where were you putting the attenuators? Where your signal comes into your property, or right "in front" of the tivo?

Some alternate ideas:

Getting all channels but premium could be a pairing/authorization issue. It took the cablecard hotline group THREE tries to get my Roamio right a few days ago. First call got me con:, second val: the third try got me my full channel lineup.

Does on-demand freeze immediately after starting, or randomly?
If it freezes right away, there have been threads about needed ing to add authorization to your account with Comcast. Something about adding it under the "bolt-ons" section... Search for the thread on here.


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## triftraf (Jan 26, 2006)

I am having problems where my new roamio stops tuning all channels on all 6 tuners. First time I called TiVo they told me to get attenuators cause my signal strength is 100 and SNR is 45. I have not done this cause I had a premiere on the same coax and never had any probs. 

It has happened a couple times now for me on the roamio. My SNR is 11 when no coax attached. Anybody know what the acceptable value is when no coax? I assumed it should go to 0. 

The premier which is now relocated to a different area of the house drops from 35SNR and 90% SS to 0 when the coax is pulled.


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## kbmb (Jun 22, 2004)

triftraf said:


> I am having problems where my new roamio stops tuning all channels on all 6 tuners. First time I called TiVo they told me to get attenuators cause my signal strength is 100 and SNR is 45. I have not done this cause I had a premiere on the same coax and never had any probs.
> 
> It has happened a couple times now for me on the roamio. My SNR is 11 when no coax attached. Anybody know what the acceptable value is when no coax? I assumed it should go to 0.
> 
> The premier which is now relocated to a different area of the house drops from 35SNR and 90% SS to 0 when the coax is pulled.


On my Roamio Basic, with coax I get roughly 92-99% signal and ~38 dB SNR. When I pull the coax, signal goes to - and SNR is either 9 or 15 dB.

With the coax in, the OOB SNR is ~400 dB (no ideas why this number is so different on the Basic compared to the Pro)

Without the coax the OOB SNR is ~45 dB

BTW...haven't had any tuning problems. I'm on Comcast NE with NO tuning adapter.

*EDIT:*
Checked my Pro:

With coax, signal levels 94-100%, SNR 37-40 dB. OOB SNR 32 dB.

Without coax, signal levels -, SNR 11-22 dB. OOB SNR 124 dB ?!?!

Haven't had tuning issues with this one either.

-Kevin


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## CrispyCritter (Feb 28, 2001)

triftraf said:


> I am having problems where my new roamio stops tuning all channels on all 6 tuners. First time I called TiVo they told me to get attenuators cause my signal strength is 100 and SNR is 45. I have not done this cause I had a premiere on the same coax and never had any probs.


There are major differences between the Roamio and Premiere response to signal strength. The Roamio is much more sensitive. People have said that the Roamio has an internal amplifier to split the signal over the 6 tuners.

Lots of people have been helped with attenuators when their SNR is that high; it's a reasonable thing to try.


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## CrispyCritter (Feb 28, 2001)

Duplicate post, sorry.


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## kbmb (Jun 22, 2004)

triftraf said:


> I am having problems where my new roamio stops tuning all channels on all 6 tuners. First time I called TiVo they told me to get attenuators cause my signal strength is 100 and SNR is 45. I have not done this cause I had a premiere on the same coax and never had any probs.
> 
> It has happened a couple times now for me on the roamio. My SNR is 11 when no coax attached. Anybody know what the acceptable value is when no coax? I assumed it should go to 0.
> 
> The premier which is now relocated to a different area of the house drops from 35SNR and 90% SS to 0 when the coax is pulled.


I would at a minimum, throw a 2 or 3-way splitter in front of the Tivo to bring the SNR down under 100. Once you find how much you need, then you can order attenuators.

-Kevin


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## triftraf (Jan 26, 2006)

I did call TiVo again about this today. This tech says I may have fried my unit with too much signal. Since I'm within my 30 days on my Roamio Pro - they are RMA-ing it...

After getting off the phone - I did put a 2way splitter on it (-3.5db) - and it reduced signal to high 90's and lowered the SNR a little. So, I'm wondering do I even need an attenuator if I just add a splitter?

The TiVo rep suggested I wanted signal in the 70's... Which I know on Premier or older boxes sometimes I had issues when the signal was in the low 70's... So that sounds pretty low...


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## steve614 (May 1, 2006)

triftraf said:


> The TiVo rep suggested I wanted signal in the 70's... Which I know on Premier or older boxes sometimes I had issues when the signal was in the low 70's... So that sounds pretty low...


You can't compare the signal as reported between different model TiVos. They may not be using the exact same parameters in measuring the signals.


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## kbmb (Jun 22, 2004)

triftraf said:


> I did call TiVo again about this today. This tech says I may have fried my unit with too much signal. Since I'm within my 30 days on my Roamio Pro - they are RMA-ing it...
> 
> After getting off the phone - I did put a 2way splitter on it (-3.5db) - and it reduced signal to high 90's and lowered the SNR a little. So, I'm wondering do I even need an attenuator if I just add a splitter?
> 
> The TiVo rep suggested I wanted signal in the 70's... Which I know on Premier or older boxes sometimes I had issues when the signal was in the low 70's... So that sounds pretty low...


Well according to this page on Tivo, the unit should have protected itself if signal too high:

http://support.tivo.com/app/answers/detail/a_id/150



> NOTE: If your signal strength is at 100 and the video looks fine, this is not an error. The signal strength meter sets 100 as a safe threshold. If the signal is at this threshold or a bit beyond, your picture quality should be excellent. *If the signal strength is well beyond the threshold, it will still register as 100, but you might experience poor picture quality, as some DVR components cycle in and out of "protect" mode to prevent damage*.


As for the splitter, as far as I know it's doing the same thing an attenuator would do.....so if it's working for you, just leave it on.

-Kevin


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## mae (Dec 10, 2001)

kbmb said:


> As for the splitter, as far as I know it's doing the same thing an attenuator would do.....so if it's working for you, just leave it on.


If you use a splitter as an attenuator, you should cap any unused ports with a 75 ohm terminator to avoid other problems.


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## dlongnecker (Dec 31, 2006)

kbmb said:


> I would at a minimum, throw a 2 or 3-way splitter in front of the Tivo to bring the SNR down under 100. Once you find how much you need, then you can order attenuators.
> 
> -Kevin


From the outside wall to my tivo, it goes through three splitters. I have tried various attenuators in different locations, but no success. I am now on my sixth cable card and about my 20th call to comcast. I do call the comcast CABLECARD number...once in awhile it is connected to someone who obviously doesn't know what he is doing, so I hang up and call again.

So right now my two problems are. 1 no premium channels and 2 VOD freezes after 5 seconds. I have asked all the questions about things turned on, etc. but no help.


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## boulderskies (Aug 23, 2013)

How do I find the SNR on a basic Roamio?



dlongnecker said:


> I've been trying to troubleshoot the problem with my new Roamio not getting authorized for about 3 weeks. While both Tivo and Comcast are trying to be helpful, its not going anywhere. (I'm getting all channels but the premium ones and VOD freezes.).
> 
> Tivo claims my SNR is too high. Its at the 42 level. Tried putting attenuators in place, to get it down to 36, but then I lose my internet connection.
> 
> ...


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## jmbach (Jan 1, 2009)

dlongnecker said:


> From the outside wall to my tivo, it goes through three splitters. I have tried various attenuators in different locations, but no success. I am now on my sixth cable card and about my 20th call to comcast. I do call the comcast CABLECARD number...once in awhile it is connected to someone who obviously doesn't know what he is doing, so I hang up and call again.
> 
> So right now my two problems are. 1 no premium channels and 2 VOD freezes after 5 seconds. I have asked all the questions about things turned on, etc. but no help.


What cableCARD are you using. (brand and firmware version) I have read in different threads that the VOD freeze after 5 seconds is a "feature" option that needs to be added on at the head end. ( http://www.tivocommunity.com/tivo-vb/showthread.php?p=9809508#post9809508) The no premium channel problem is a pairing problem. I have Charter and when I have replaced the drive in my TiVo(s) with a new image, I lose the pairing. In my area they use Motorola M-Cards. These cards have a habit of generating new data ids when the drive is replaced or if you eject the card and reinsert it. The Charter techs check the S/N, Host ID, and cableCARD ID which does not change. All they want to do is send hits to the card and have me reboot the TiVo. I tell them about the Data ID and they either tell me it does not matter or lie to me that it is the same. Then they want to roll a truck. In the end I either call back or ask for the next supervisor above the person I am talking to. Eventually I get to someone who listens and does check the Data ID. Why I know they lie? Because when I finally get someone to check the Data ID, it is different and as soon as they change it to what my M-Card Data ID is, I am back up, paired, and have all my premium channels.
From what I have read in the threads, the Cisco/Scientific Atlanta cards don't have this issue.


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## L David Matheny (Jan 29, 2011)

dlongnecker said:


> I've been trying to troubleshoot the problem with my new Roamio not getting authorized for about 3 weeks. While both Tivo and Comcast are trying to be helpful, its not going anywhere. (I'm getting all channels but the premium ones and VOD freezes.).
> 
> Tivo claims my SNR is too high. Its at the 42 level. Tried putting attenuators in place, to get it down to 36, but then I lose my internet connection.
> 
> ...


My 4-tuner Roamio sometimes has trouble with a local PBS channel that has severe multipath problems. Right now DVR Diagnostics show something like:

Signal Strength: 50%
Signal Lock: Yes
Program Lock: Yes
...
SNR: 20dB
RS Uncorrected: 2164260735
RS Corrected: 0

Uncorrected errors are not incrementing (much), and reception is fine. But earlier today I saw a V53 error and diagnostics something like:

Signal Strength: -
Signal Lock: No
Program Lock: Yes
...
SNR: 19dB
RS Uncorrected: 2160000000 [millions less, but I don't remember]
RS Corrected: 0

And even with no (useable) signal, the uncorrected errors were climbing wildly. It appears that if the signal goes away, some of the other items just don't get updated, but errors are still counted even though they're meaningless. It doesn't make sense to say that there is no (useable) signal and synchronization with the transmitter has been lost, but yet the unit is locked onto a transport stream and able to count errors and calculate a SNR.

IOW, if you disconnect your cable, any SNR shown is just a bogus artifact. And I will mention again that I have never seen the Roamio show any count of corrected errors. TiVo needs to clean up their software.


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## nooneuknow (Feb 5, 2011)

L David Matheny said:


> IOW, if you disconnect your cable, any SNR shown is just a bogus artifact. And I will mention again that I have never seen the Roamio show any count of corrected errors. TiVo needs to clean up their software.


I've found that most of the time, *if a Tuning Adapter is involved*, that corrected and uncorrected stay at zero in DVR Diags, but can be found under Tuning Adapter Diags.

It's usually oddball situations, like you describe, where the uncorrected just keeps going forever, and everything else is also wonky in DVR Diags.

I'm guessing that since a TA takes over tuning all channels, not just SDV, that it either makes sense that the cablecard entries in DVR diags are usually always at zero corrected/uncorrected (and is technically correct), or it could just be TiVo being lazy in carrying over the values. Perhaps it isn't as easy as one might think to carry over the values...

Could you please educate me on what "multipath problems" are? It sounds like something I should know about.

I'll probably find it with google, but I'd appreciate it in your own context.


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## andyf (Feb 23, 2000)

MultiPath is where the source signal (transmitter) bounces off objects (such as high rise buildings etc) such that the receiver (your antenna) receives multiple signals but off phase which can cause ghosting (in analog TVs) or interference.

I'll let the experts explain better.


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## L David Matheny (Jan 29, 2011)

nooneuknow said:


> I've found that most of the time, *if a Tuning Adapter is involved*, that corrected and uncorrected stay at zero in DVR Diags, but can be found under Tuning Adapter Diags.
> 
> It's usually oddball situations, like you describe, where the uncorrected just keeps going forever, and everything else is also wonky in DVR Diags.
> 
> ...


I think cable tuning is done by the cablecard, with the tuning adapter translating channel numbers so that the cablecard tunes the right physical channel and shows the right virtual channel number. In any case, I'm OTA only, so of course I have neither. If the tuner/demodulator chipset in my 4-tuner Roamio is operating correctly, I would think that there surely should be some correctable errors, yet none are ever shown in DVR Diagnostics, so maybe the TiVo isn't reading some chipset register correctly. And even if the chipset makes the mistake of continuing to count uncorrectable errors when no data is passing through it, the TiVo software should know to ignore those errors as meaningless.

The multipath I was referring to is multipath interference, which can cause intermittent fading of broadcast signals, leading to signal strength fluctuation and digital dropouts. It can be static (from nearby buildings, bridges, hills, etc) or dynamic (from passing planes or trucks, moving tree branches, etc). Modern digital tuner/demodulator chipsets use digital signal processing to recognize and cancel out multipath signals within limits, but if the reflected signals are too strong or the delay is too great, the capabilities of the chipset can be overwhelmed. I'm no expert, but you can Google it for more. I believe some of my signals suffer from much static multipath, but little dynamic multipath.


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