# Need help to lower SNR TiVo says its to high



## Jed1 (Jun 18, 2013)

I received another response back from TiVo Support as they are helping me out with the black screen issue.
They stated that my incoming signal is in an ideal range at 88 to 92% but my SNR of 36db to 37db is to high and I need to get it down to around 32db. 
The only problem is they did not tell me how to do this. I did email them back and asked them what the SNR is and how to reduce it but it may take a few days to get a response. 

Can anybody give me some advice on how to do this? I will be greatly appreciated as I really want to get this issue behind me.


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## Dan203 (Apr 17, 2000)

Just use a splitter. Every leg of a splitter loses 3.5db so that should get you close. If it's not enough you can use a 3 or 4 way splitter, then you'll lose 7db. (if you use a 3 way make sure to use the leg that says -7db on it)


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## Phantom Gremlin (Jun 20, 2002)

Jed1 said:


> They stated that my incoming signal is in an ideal range at 88 to 92% but my SNR of 36db to 37db is to high and I need to get it down to around 32db.


TiVo has been making this claim for many years. I know they made it with the HD, do they still make it with the Roamio? I don't see you mention the box you have.

It's probably not complete ********, but it's also probably not entirely accurate. My HD is upstairs, but I'm in front of my Roamio. I will give you the following for each of 6 tuners:

tuner, frequency, signal strength, SNR, RS uncorrected, RS corrected, time since signal lock

sorry about the formatting, there is probably a way to make it pretty but you'll get the idea anyway.

0, 291000, 100%, 40 dB, 0, 15, 18136
1, 423000, 100%, 40 dB, 0, 15, 18190
2, 297000, 100%, 40 dB, 0, 22, 18212
3, 435000, 100%, 40 dB, 0, 3, 18242
4, 387000, 100%, 40 dB, 0, 16, 18264
5, 531000, 99%, 39 db, 0, 0, 18300

As you can see my signal strength and SNR are much higher than TiVo claims is good, and yet my errors are non-existent.

I'm not sure why all my times are so close to each other, I didn't reboot the box recently.

Edit: here are the values from my TiVo HD. Also quite high, no errors.

0, 321000, 100%, 36 dB, 0, 0, 38707
1, 201000, 100%, 36 dB, 0, 0, 25925

Both the Roamio and the HD are fed from the same splitter. The arrangement is something like this:

Comcast cable ->
1:2 splitter (other split to cable modem) ->
15 dB Motorola signal booster ->
1:4 splitter ->
up to 4 TiVo boxes

The cable modem I have lets me read signal strength received and it's about -5 dB. So that means that as supplied by Comcast my signal is about 0 dBmv.

Each TiVo sees (roughly)
0 dBmV from Comcast
-4 dB splitter
+15 dB amp
-8 dB splitter
-2? dB coax losses

0 - 4 + 15 - 8 - 2 = approx 1 dBmV at the coax input to the TiVo box.

Anyway, that's just some data. I'm sure there are real problems that many people have, but I'm also sure it's not just signal strength and SNR that are the magic solutions. It's possible that poor home coax or poor splitters or high intermodulation distortion from a cheap amplifier are causing your problems. Or it could be some other problem, I'm certainly not an expert in this area.

One thing I would try if at all possible: Take the TiVo into the garage (or wherever your cable comes in). Plug in directly there, ahead of any house wiring or splitters. Does it work OK? If so, that's a starting point.


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## Wil (Sep 27, 2002)

Trying to improve signal to noise ratio by simply attenuating the signal, e.g. with a splitter, is not going to work. The splitter will reduce both signal and noise, proportionately, with no beneficial effect on the ratio; in fact the splitter and its connections are going to add noise even if perfectly shielded (impossible) so the ratio declines (gets worse). This is an oversimplification because the splitter's effect on signal is not flat over the entire bandwidth so the impact will be less at certain specific frequencies but the signal to noise CAN'T improve on average over the range.

You have to increase the signal while increasing (unavoidably) the noise less than proportionately. There's no magic; that's it. Better aiming of the antenna, a better antenna, a high grade low noise preamp. If you're dealing with a cable signal your provider needs to measure their tap to your location and tweak.

EDITED TO ADD: BTW a signal to noise ratio is a number, a ratio or less often a percentage, no units like db, which apply to the signal and the noise themselves, respectively. Sometimes the DIFFERENCE between signal and noise is expressed in db's but that's pretty meaningless without the signal level as a reference.


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## JoeKustra (Dec 7, 2012)

Jed1 said:


> I received another response back from TiVo Support as they are helping me out with the black screen issue.
> They stated that my incoming signal is in an ideal range at 88 to 92% but my SNR of 36db to 37db is to high and I need to get it down to around 32db.
> The only problem is they did not tell me how to do this. I did email them back and asked them what the SNR is and how to reduce it but it may take a few days to get a response.
> 
> Can anybody give me some advice on how to do this? I will be greatly appreciated as I really want to get this issue behind me.


TiVo is strange. Anyhow, my Premiere with a cable card records almost daily. Its numbers:
ch 515 159MHz (I record with this tuner)
81%
36 dB SNR
848 RS Corrected
51960 RS Uncorrected
460k seconds since tune start
ch 564 513MHz
89%
36 dB SNR
0 RS Corrected
5 RS Uncorrected
615k seconds since tune start
Box was powered on about a week ago and has also recorded ABC twice. OOB SNR is 2 dB.

My Roamio diagnostics can't be trusted. My cable modem still gets about 500 to 1000 bad blocks (almost) daily on 507MHz only.

I agree with the previous posts. You probably can't alter your SNR only your signal %.* I have a variable attenuator if you want to try*. There are probably few things you haven't tested, but if I had this problem here are a few thoughts.

Does the TV indicate lack of signal? Do the tuner counter(s) reset to zero? Does it ever happen during playback? Is this a frequent problem? I would gladly let you use my basic 320GB Premiere for a while if you feel it would help. I only use it for a few hours in the morning and it does have a cable card but no premium channels. I don't know if SECV would be happy doing it either. I'm glad to help if you think of something.


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## snerd (Jun 6, 2008)

Wil said:


> Trying to improve signal to noise ratio by simply attenuating the signal, e.g. with a splitter, is not going to work. The splitter will reduce both signal and noise, proportionately, with no beneficial effect on the ratio; in fact the splitter and its connections are going to add noise even if perfectly shielded (impossible) so the ratio declines (gets worse). This is an oversimplification because the splitter's effect on signal is not flat over the entire bandwidth so the impact will be less at certain specific frequencies but the signal to noise CAN'T improve on average over the range.
> 
> You have to increase the signal while increasing (unavoidably) the noise less than proportionately. There's no magic; that's it. Better aiming of the antenna, a better antenna, a high grade low noise preamp. If you're dealing with a cable signal your provider needs to measure their tap to your location and tweak.


You're right, but TiVo CSRs are saying the SNR needs to be reduced. Which means either the CSRs don't know what they are talking about (often true) or the SNR that the box lists doesn't really mean "Signal to Noise Ratio".

It is possible for signal strength to be too high, and in that case attenuation is the correct remedy.

Clueless CSR seems most plausible to me. There is no way that decreasing SNR can have any benefit.


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## snerd (Jun 6, 2008)

Wil said:


> EDITED TO ADD: BTW a signal to noise ratio is a number, a ratio or less often a percentage, no units like db, which apply to the signal and the noise themselves, respectively. Sometimes the DIFFERENCE between signal and noise is expressed in db's but that's pretty meaningless without the signal level as a reference.


Actually, dB is often used to express a ratio. SNR = log(S/N) is a perfectly acceptable way to express SNR, and every increase of 10 dB means a factor of 10 increase in SNR, so 40dB is an SNR of 10,000.


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## Dan203 (Apr 17, 2000)

snerd said:


> the SNR that the box lists doesn't really mean "Signal to Noise Ratio".


I think this might be the case, because several people have had success attenuating the signal and when they do the value on that screen drops.

I still think he should try the splitter. If it doesn't help then he can go back to support and ask for annother possible solution.


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## Wil (Sep 27, 2002)

Dan203 said:


> I still think he should try the splitter.


Attenuating a signal that's too hot sometimes helps (I'm just saying NOT for signal noise improvement). Also if there's multipath the crudity and variation of the attenuation effect over the range can sometimes match up well with your problem and you get lucky.

Some cable company contractors carry attenuators tuned to various specific ranges along the spectrum and if you can persuade one to give you a bunch they're useful for experimenting. A reasonable approach to some problems is to put in a very low noise amp on the signal then apply the attenuators trial and error to try to bring back down any channels that become amped up too hot. Of course if you've got a meter you can be a lot more organized about it but they're very expensive.


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## snerd (Jun 6, 2008)

Dan203 said:


> I still think he should try the splitter. If it doesn't help then he can go back to support and ask for annother possible solution.


Can't hurt to try. In order to use a splitter as an attenuator, it is important to place 75-ohm terminations on the unused outputs of the splitter.


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## Jed1 (Jun 18, 2013)

Dan203 said:


> Just use a splitter. Every leg of a splitter loses 3.5db so that should get you close. If it's not enough you can use a 3 or 4 way splitter, then you'll lose 7db. (if you use a 3 way make sure to use the leg that says -7db on it)


Well this did not work. I tried a 4 way first and nothing really changed at all as the SNR stayed at 36dB to 37dB. 
By adding in another 2 way for -12dB the only change was the signal strength dropped to 82% to 88%.
Taking out the 2 way and adding another 4 way for -16dB, it did manage to drop the SNR to 34dB on some channels but I lost a little more signal strength and I had some channels that were tiling and had audio dropouts. Those channels had corrected and uncorrected errors. I also found a couple of channels that did not work and had a V52 error. The signal strength was in the 70% range.
By adding in the 2 way again for a total of -20dB I finally got all the channels down to 32dB but a lot of them were not working and getting V52 errors. The channels that were working was tiling and getting a lot of corrected and uncorrected errors. The signal strength was in the high 60% to low 70% range. 
I did use those terminators that were mentioned.

It seems that up to -12dB nothing affects the signal, then after that it is like the signal falls off of a cliff and just gets worse as more or the signal is lost.


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## unitron (Apr 28, 2006)

Saying that your Signal to Noise Ratio is too high is saying that there's not enough noise in the signal, that the quality of the signal is too good.

Which is kind of like saying that there's not enough poison in your drinking water.


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## Dan203 (Apr 17, 2000)

Jed1 said:


> Well this did not work. I tried a 4 way first and nothing really changed at all as the SNR stayed at 36dB to 37dB.
> By adding in another 2 way for -12dB the only change was the signal strength dropped to 82% to 88%.
> Taking out the 2 way and adding another 4 way for -16dB, it did manage to drop the SNR to 34dB on some channels but I lost a little more signal strength and I had some channels that were tiling and had audio dropouts. Those channels had corrected and uncorrected errors. I also found a couple of channels that did not work and had a V52 error. The signal strength was in the 70% range.
> By adding in the 2 way again for a total of -20dB I finally got all the channels down to 32dB but a lot of them were not working and getting V52 errors. The channels that were working was tiling and getting a lot of corrected and uncorrected errors. The signal strength was in the high 60% to low 70% range.
> ...


You don't want to use terminators. Those essentially negate the drop introduced by the split.


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## Wil (Sep 27, 2002)

snerd said:


> Can't hurt to try. In order to use a splitter as an attenuator, it is important to place 75-ohm terminations on the unused outputs of the splitter.


Yes; any time there is an unused output on a splitter (a similar-looking "tap" has other characteristics), whether being used as an attenuator or not. The terminator puts a load at that output, otherwise you're going to get signal echo, impedance issues and other stuff that's not going to do any good at all! It has nothing to do with attenuation itself and whether the attenuation happens or not; always use a terminator.


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## snerd (Jun 6, 2008)

Dan203 said:


> You don't want to use terminators. Those essentially negate the drop introduced by the split.


No, they don't. Terminations prevent reflections from causing fluctuations in signal strength throughout the system. A 2-way splitter with a termination on one output port will have about 3.5 dB insertion loss, just as it should. Similarly, a 4-way splitter with three terminations will have about 7dB insertion loss.

Oops, sorry for the smeek, I agree with Wil.


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## Dan203 (Apr 17, 2000)

Ahh OK, I thought the terminators were used to prevent the loss on unused ports.


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## JoeKustra (Dec 7, 2012)

Dan203 said:


> Ahh OK, I thought the terminators were used to prevent the loss on unused ports.


A good supply. I think 10 will last a while. http://www.amazon.com/Type-75-Ohm-T...ie=UTF8&qid=1445884142&sr=8-1&keywords=75+ohm


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## Dan203 (Apr 17, 2000)

I have a bunch already, I just apparently didn't understand their exact purpose.


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## aaronwt (Jan 31, 2002)

Jed1 said:


> I received another response back from TiVo Support as they are helping me out with the black screen issue.
> They stated that my incoming signal is in an ideal range at 88 to 92% but my SNR of 36db to 37db is to high and I need to get it down to around 32db.
> The only problem is they did not tell me how to do this. I did email them back and asked them what the SNR is and how to reduce it but it may take a few days to get a response.
> 
> Can anybody give me some advice on how to do this? I will be greatly appreciated as I really want to get this issue behind me.


 Pick up an attenuator. I got this 6dB attenuator from Amazon for my Roamio Pro on FiOS. It's only $2.99 right now and is an Amazon Add On item.

http://www.amazon.com/gp/product/B004C5P9MI?psc=1&redirect=true&ref_=oh_aui_search_detailpage


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## slice1900 (Dec 2, 2005)

It is impossible for the SNR to be "too high". The signal power could be too strong, though at 88-92% while you're at the top end of what the AGC can handle you should be fine. I think Tivo is making up excuses for a problem they haven't figured out yet.


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## aaronwt (Jan 31, 2002)

slice1900 said:


> It is impossible for the SNR to be "too high". The signal power could be too strong, though at 88-92% while you're at the top end of what the AGC can handle you should be fine. I think Tivo is making up excuses for a problem they haven't figured out yet.


The attenuator solved my problem with a specific channel.. The channel shows a strong signal and a high 37/38dB SNR with a Black screen. As soon as I put the attenuator on the input I get a picture back. I remove the attenuator the picture goes to black again. I put the attenuator on and the picture comes back.


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## Wil (Sep 27, 2002)

snerd said:


> Actually, dB is often used to express a ratio.


Isn't that Signal to Noise Margin? Not exactly the same as the ratio (but higher is still better)? Long time out of school.

Maybe when Tivo is talking about reducing SNR they really mean reduce the Noise itself?


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## Dan203 (Apr 17, 2000)

I think they are just saying the signal is too hot. Maybe they assume a SNR that's over 32 indicates a hot signal.


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## dlgamble (Oct 3, 2015)

My new Roamio Plus shows a signal level of 100% on all channels. Should I add an attenuator or wait and see if any issues arise?


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## JoeKustra (Dec 7, 2012)

dlgamble said:


> My new Roamio Plus shows a signal level of 100% on all channels. Should I add an attenuator or wait and see if any issues arise?


Please wait. My basic Roamio is 87/90 on all channels and a 35/36 dB respectively. I once saw 92 I think. If you have a cable signal giving you 100 it's either a new version of "something", or we have a new issue.

Also, what's your SNR and MBT? Thanks.

Also, you said all channels. Is it all tuners too?


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## kbmb (Jun 22, 2004)

dlgamble said:


> My new Roamio Plus shows a signal level of 100% on all channels. Should I add an attenuator or wait and see if any issues arise?


Don't touch it unless you have problems. TiVo doesn't have a clue of what they are doing. To make matter worse, signals on the Plus/Pro are completely different than the Basic. So in TiVo's world.....I can put a Basic on my line and have perfect signals.....but a Plus on the same line the signals are too high. That's not my line TiVo....that's YOUR box!

I just imagine first line TiVo tech support a bunch of robot zombies reading off a script......SIGNAL.....TOO......HOT........MUST......REDUCE!!!

-Kevin


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## JoeKustra (Dec 7, 2012)

kbmb said:


> Don't touch it unless you have problems. TiVo doesn't have a clue of what they are doing. To make matter worse, signals on the Plus/Pro are completely different than the Basic. So in TiVo's world.....I can put a Basic on my line and have perfect signals.....but a Plus on the same line the signals are too high. That's not my line TiVo....that's YOUR box!
> 
> I just imagine first line TiVo tech support a bunch of robot zombies reading off a script......SIGNAL.....TOO......HOT........MUST......REDUCE!!!
> 
> -Kevin


You are right about that. I didn't realize there was so much difference between the models. Thanks for the information.

However, none of this helps Jed1 since he has Premieres. In case you have not noticed, Jed1 and I are about 6 miles apart with the same cable company.


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## kbmb (Jun 22, 2004)

JoeKustra said:


> You are right about that. I didn't realize there was so much difference between the models. Thanks for the information.


My Basic with get the typical 92-95 signal with 35/36 dB SNR.

On the same line my Plus needs to be attenuated to get 99-100 signal and 40 db SNR.

I can switch them and the signal levels follow the box.

-Kevin


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## dlgamble (Oct 3, 2015)

JoeKustra said:


> Please wait. My basic Roamio is 87/90 on all channels and a 35/36 dB respectively. I once saw 92 I think. If you have a cable signal giving you 100 it's either a new version of "something", or we have a new issue.
> 
> Also, what's your SNR and MBT? Thanks.
> 
> Also, you said all channels. Is it all tuners too?


The SNR is 40. That is all channels and all tuners. I don't remember the MBT. (Not at home right now.)


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## dlgamble (Oct 3, 2015)

kbmb said:


> Don't touch it unless you have problems. ...
> 
> -Kevin


Thanks. That's what I thought. I did notice that my old P4 has lower signal strength numbers on the same cable. I have never had any problems with it. I guess that the meter is more sensitive in the R+.


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## thefisch (Jul 25, 2015)

kbmb said:


> My Basic with get the typical 92-95 signal with 35/36 dB SNR.
> 
> On the same line my Plus needs to be attenuated to get 99-100 signal and 40 db SNR.
> 
> ...


I get the same results if I switch the same line between my plus and basic.


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## Dan203 (Apr 17, 2000)

I think the Plus/Pro has a built in amp while the basic does not, so the built in amp might over amp the signal if you have a strong signal going in.


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## kbmb (Jun 22, 2004)

Dan203 said:


> I think the Plus/Pro has a built in amp while the basic does not, so the built in amp might over amp the signal if you have a strong signal going in.


Nothing like having TiVo tell people to attenuate their signals just so their crappy amp can bring them up again. 

-Kevin


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## aaronwt (Jan 31, 2002)

Dan203 said:


> I think the Plus/Pro has a built in amp while the basic does not, so the built in amp might over amp the signal if you have a strong signal going in.


That certainly explains the signal results seen between the Pro/Plus and the Basic/Bolt.


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## Jed1 (Jun 18, 2013)

OK. TiVo Support says that I must use attenuators instead of splitters. I got a very confusing reply but I think they wanted me to change the coaxial cable coming into the TiVo. That made no difference. I did borrow some attenuators but I got the same result.
I normally do not post email replies but I will do so in this case as it is some what confusing.


> Instead of operating with a splitter to lower that SNR value, try adding a signal attenuator. If the signal continues to drop below 80% while the incoming SNR range is at 32-34dB, *you may try swapping the coaxial connection in use to level the amount of noise and manage the signal strength.*


I have also noticed that there is at least five different people who are replying to my emails. I do not think they are all on the same page.
The good thing to report is I got my cards back in proper operation this morning after the Thursday three way call debacle.


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## HarperVision (May 14, 2007)

Dan203 said:


> Ahh OK, I thought the terminators were used to prevent the loss on unused ports.


No, they're basically just "dummy loads". We used to have giant ones that could take our 10KW TV transmitter outputs when we were testing or couldn't transmit while over land. They simulate a real 75 ohm device like a video display or tuner, etc.


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## HarperVision (May 14, 2007)

slice1900 said:


> It is impossible for the SNR to be "too high". The signal power could be too strong, though at 88-92% while you're at the top end of what the AGC can handle you should be fine. I think Tivo is making up excuses for a problem they haven't figured out yet.


Agreed. I've been saying this for years and to this day don't know why they say this.


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## dlfl (Jul 6, 2006)

slice1900 said:


> It is impossible for the SNR to be "too high". The signal power could be too strong, though at 88-92% while you're at the top end of what the AGC can handle you should be fine. I think Tivo is making up excuses for a problem they haven't figured out yet.





Dan203 said:


> I think they are just saying the signal is too hot. Maybe they assume a SNR that's over 32 indicates a hot signal.





HarperVision said:


> Agreed. I've been saying this for years and to this day don't know why they say this.


This. TiVo circuits/software must not actually measure SNR. No one has ever explained why a signal strength of (for example) 95 with a SNR of 33 dB is better than the same signal strength with 37 or 40 dB SNR. In other words, why less noise with the same signal strength is bad.


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## Jed1 (Jun 18, 2013)

I want to admit that I was being a bit disingenuous when I started this thread. I am actually in the know when it comes to the engineering and operation of cable TV.
I started down his road when I again had enough of the black screen issue with my TiVo's. Of course I had to go in for another abusive round with TiVo Support and I got bombarded with this SNR is to high nonsense. So that call did not go well so I decided to go the email route and then go through the actual steps they wanted me to. The one caveat was I already had the exact power and noise readings for my entire downstream spectrum.
This is the meter that was used to get those readings. This analyzer is $6000.
http://www.viavisolutions.com/sites/default/files/technical-library-items/dsam6300-ds-cab-tm-ae.pdf
http://www.viavisolutions.com/en/pr...docsis-eurodocsis-capabilities#fndtn-overview
http://www.acternacablenet.com/downloads/dsam/DSAM_Manual.pdf

Now I do want to state that one poster in this thread got it right and that was Wil. He gets the gold star. Also when you are dealing with digitally modulated signals it is MER (modulation error rate) that is used. SNR or CNR is mainly used for analog signals. MER is actually the same thing as SNR so the terms are interchangeable.
https://en.wikipedia.org/wiki/Modulation_error_ratio
https://en.wikipedia.org/wiki/Carrier-to-noise_ratio
https://en.wikipedia.org/wiki/Signal-to-noise_ratio

Here is the official definition of SNR:


> Signal-to-noise ratio is also called as SNR or S/N, is defined as the ratio of signal power to the noise power corrupting the signal. The Signal to Noise Ratio (SNR) is the defining factor when it comes to quality of measurement. *A high SNR guarantees clear acquisitions with low distortions and artifacts caused by noise. The better your SNR, the better the signal stands out, the better the quality of your signals, and the better your ability to get the results you desire.* SNR measurement is commonly used in the field of science and engineering. A ratio higher than 1:1 indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can be applied to any form of signal.


The one thing that I can state is the signal strength meter on the TiVo is unreliable and not accurate. Since I knew what my exact readings are I could not correlate what the signal strength was a percentage of. Nothing made any sense. Since SNR is a ratio reading I could not figure out what two measurements was being used to get that reading. My TiVo's is under reporting the SNR by about 4dB. My SNR readings are around 40dB across the down stream spectrum.
My signal is relatively flat across the down stream spectrum and may vary by 4dBmV. I readily knew how much attenuation I could apply that would start causing some channels to tile and have audio drop outs. After that pint it was predictable what channels would stop working as more signal loss was applied.

Another frustrating thing I came across with TiVo Support is they never asked what the frequency of the channel they were taking the readings from.
I kept asking the support person if he was sure he did not need it. The reason I kept asking was all 4 of my tuners were tuned to channels in the mid band to high band VHF spectrum. The channels were with in 60 Mhz of each other.
When I was going through Support by email they never even asked for readings for any specific channel. They stated that my SNR was to high and I needed to lower it. I gave them an average SNR of 36dB and they insisted to lower it to 32dB for optimum performance. They stated my 88% to 90% signal strength was good.

If you want to properly trouble shoot cable TV signals you first need a channel frequency chart and always use the frequency of the channel to locate the actual portion of the spectrum you are dealing with. Here is two charts that are pretty accurate.
This one is pdf document so you can save it for reference:
http://eaglecomtronics.com/Cable_Television_Channel_-_Frequency_Chart.pdf
This chart is for cable and over the air frequency:
https://en.wikipedia.org/wiki/North_American_television_frequencies#Cable_television

The sad thing about all this is it is damaging to TiVo themselves because at the end of the day sending customers on wild goose chases only frustrates the TiVo customer. People telling the cable operators that the SNR is to high just results in them not taking TiVo seriously. Cable Television in North America is engineered to one standard some all traditional HFC operators work the same way. If TiVo's are not built to the standard then it is TiVo's issue alone.
My intent here is to set the story straight and get everybody working on the same page. This can only benefit TiVo in the long run. So if you really care about TiVo please stop spreading this nonsense about the SNR is to high.


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## HarperVision (May 14, 2007)

Jed1 said:


> I want to admit that I was being a bit disingenuous when I started this thread. I am actually in the know when it comes to the engineering and operation of cable TV.
> I started down his road when I again had enough of the black screen issue with my TiVo's. Of course I had to go in for another abusive round with TiVo Support and I got bombarded with this SNR is to high nonsense. So that call did not go well so I decided to go the email route and then go through the actual steps they wanted me to. The one caveat was I already had the exact power and noise readings for my entire downstream spectrum.
> This is the meter that was used to get those readings. This analyzer is $6000.
> http://www.viavisolutions.com/sites/...-cab-tm-ae.pdf
> ...


Amen brutha!

Could that 4db difference you're seeing be maybe a normal signal drop or loss at the TiVo's RF coax input but when you use your meter it's not connected to that of course?


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## Jed1 (Jun 18, 2013)

HarperVision said:


> Amen brutha!
> 
> Could that 4db difference you're seeing be maybe a normal signal drop or loss at the TiVo's RF coax input but when you use your meter it's not connected to that of course?


I actually took the readings from the coax that feeds the TiVo. When I look at my notes I see that the average SNR is around 39dB. I do have 40dB on the 16 downstream DOCSIS channels. According to TiVo I guess my internet and phone is not working either.
The TiVo reports 36dB to 37dB for SNR. So the TiVo is reporting about 2dB to 3dB less. But I have no idea on what power readings the TiVo is using to arrive at the SNR reading.
When I had the -16dBmV attenuation applied the TiVo was reporting a power reading of 80% on some channels that were starting to fail or failing. This made no sense at all as the meter was showing the signal power around -12dBmV to -16dBmV.
What I am having a hard time figuring out is I had a 90% reading when the meter was showing around+4dBmV and then a 80% reading when I applied 16dB of attenuation. There is no logic to the TiVo signal strength reading.


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## JoeKustra (Dec 7, 2012)

Jed1 said:


> There is no logic to the TiVo signal strength reading.


You're being too kind.


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## BobCamp1 (May 15, 2002)

dlfl said:


> This. TiVo circuits/software must not actually measure SNR. No one has ever explained why a signal strength of (for example) 95 with a SNR of 33 dB is better than the same signal strength with 37 or 40 dB SNR. In other words, why less noise with the same signal strength is bad.


The Tivo power measuring circuits aren't ideal. That circuit probably has an expected range of what it can realistically measure. If you get an unrealistic measurement from that circuit, even if it's unrealistically high, then something could be wrong with the signal.

If my minivan's computer said it got 75 mpg on average, I wouldn't believe it even though higher mpg is better. I would instead think something is wrong with the car or the gasoline I put into it.

Using splitters to reduce the signal means you're only as good as your terminators, and I've seen some bad terminators. One wants to make sure they're actually 75.0 ohms and that the center pin is neither too long nor too short.

The problem is that usually in these scenarios, the MSO's cable box works just fine. The Tivo's receiver is simply not as good.


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## jonw747 (Aug 2, 2015)

I have to mention that when I bought my Roamio, I was seeing pixelaition on certain channels and not others. My FIOS DVR connected to the same 1:2 spliiter had no issues. The readings on the TiVo were all very strong, but adding attenuation (mild or severe) did not help.

What helped was replacing the RG59 house wiring with a RG6 homerun left over from when I subscribed to DirectTv. In other words, what helped my Roamio was an even stronger/cleaner signal. 

I added a 6dB attenuator just in case it was too strong of a signal for the box, but what we want first and foremost is a clean signal.

Don't believe anything the TiVo is reporting other than detected errors and by all means check various frequencies/channels.


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## Bigg (Oct 31, 2003)

Dan203 said:


> I think the Plus/Pro has a built in amp while the basic does not, so the built in amp might over amp the signal if you have a strong signal going in.


That would make sense since it has more tuners, and the Basic has to handle OTA whereas the Plus/Pro doesn't. I'd be interested to know if anyone with HFC cable has ever had an issue, or if it is only people with a FIOS/Cnici Bell type of setup. I've only ever had the opposite issue on HFC systems with high noise and poor signal quality.

My TiVo was at one point on a 1970's era 625mhz Comcast system, with most of the wiring in that neighborhood from the late '90s, and that system had all sorts of issues. At one point, the SNRs dropped about 10dB, and the channels went haywire. It cleared up a day later, so either Comcast did something, or it was weather related. The SNR readings mean _something_, but I think it's abundantly clear that whatever definition of SNR TiVo is using doesn't align with the rest of the universe, and is thus really unhelpful in comparing to other cable equipment.


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## JoeKustra (Dec 7, 2012)

Bigg said:


> That would make sense since it has more tuners, and the Basic has to handle OTA whereas the Plus/Pro doesn't. I'd be interested to know if anyone with HFC cable has ever had an issue, or if it is only people with a FIOS/Cnici Bell type of setup. I've only ever had the opposite issue on HFC systems with high noise and poor signal quality.
> 
> My TiVo was at one point on a 1970's era 625mhz Comcast system, with most of the wiring in that neighborhood from the late '90s, and that system had all sorts of issues. At one point, the SNRs dropped about 10dB, and the channels went haywire. It cleared up a day later, so either Comcast did something, or it was weather related. The SNR readings mean _something_, but I think it's abundantly clear that whatever definition of SNR TiVo is using doesn't align with the rest of the universe, and is thus really unhelpful in comparing to other cable equipment.


Dan has just scratched the surface. For comparison, I have a Premiere and a Roamio, both basic models, that get the same wiring except for the last three feet. The Roamio has a signal level of 87/90 with a SNR of 35/36 and those numbers always pair up even while watching. The Premiere can vary from 75 to 87 and SNR is 35/36. I have regular old cable and over the last two years I think every part has changed, including the headend equipment. I guess you could say I have a very open cable company. When I had clear QAM, they published the channels and their frequencies. My HD channels go from 141MHz to 681MHz, so it's not the frequency. If anything, it's the network feed which is all optical (locals) or satellite. So TiVo should get the diagnostics to where people can trust them, then educate the CS people that OTA is not the same as cable, and a basic Roamio is not the same as a Plus or Pro. Someday.


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## snerd (Jun 6, 2008)

Dan203 said:


> I think the Plus/Pro has a built in amp while the basic does not, so the built in amp might over amp the signal if you have a strong signal going in.


They all need a built in amp. Video equipment virtually always includes an AGC (adjustable gain circuit) as part of an internal amplifier. This is vital because the input signal strength can vary over a very wide range. A change of 10dB corresponds to a factor of 10 in RF power. However, every AGC circuit will have a limited range, so any receiver will have problems if the signal is too strong or too weak.

TiVo claiming the signal is "too hot" may mean that TiVo screwed up some of their designs by not allowing enough range on the "low gain" end. On the other hand, cable installers sometimes add amplifiers when they aren't really needed, or make other installation errors that result in a signal that is too strong, and this can be completely beyond TiVo's control.

Unfortunately, somewhere along the line TiVo CSRs have been taught the goofy notion that SNR can be "too high" when it is really signal strength that is the issue.


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## samccfl99 (Sep 7, 2013)

Dan203 said:


> I think the Plus/Pro has a built in amp while the basic does not, so the built in amp might over amp the signal if you have a strong signal going in.


I read this whole thread. I got a 3 and 6db attenuator from the comcast truck when it was in my complex. I have a Roamio Pro I got in 11-2013 and my SNR is 100% and 40-42db on all or most channels, as most people are reporting. Putting the 6db on, I only got 3db less and adding the 3db, I only got another 1db less. Why, is the first question and the other question is why have they totally stopped working after a month or so? So strange. Also they are hot to the touch. I then talked to a different comcast tech and this one told me the unit just runs hot because it is constantly on and nothing will fix it and make it "perfect" as far as Tivo support is concerned...

As stated before in this thread, the XL4 I had before, and they were once side by side using the same cable with a 2-way splitter, showed what Tivo wants to see and the Roamio Pro shows it as hot. They are constantly saying this stuff about SNR and SS. I wish they would tell the real story. If there ever is a problem and we tell them about the high signals, they always point to that and that's that.


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## Dan203 (Apr 17, 2000)

What's hot to the touch? The attenuator? Or the TiVo?


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## dlfl (Jul 6, 2006)

And what failed? TiVo(s) or attenuators?

One thing that could make an attenuator get hot (and it couldn't be the video signals) could be spurious DC coming in on the cable. A few volts on 75 ohms will make a small device like that hot. Why DC on the cable? I have no idea.


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## samccfl99 (Sep 7, 2013)

Dan203 said:


> What's hot to the touch? The attenuator? Or the TiVo?


The attenuator. The RP i never really touch. it is in a good open area. Do you have any idea why it only lowers it a bit and why they stopped working? I am confused after talking to the second comcast guy. I mean, I do not really have any problems with the box, never really had. Oh, it does little pixilations sometimes, which are normal, but not really a problem. I hardly call tech support and when they want me to go thru diagnostics with this, I say No Thank you...LOL. I missed another comcast truck yesterday. I wanted to get some more attenuators from them just to see if they would start/stop working again. I do not know if any of this is worth it. So what is your opinion Dan?

*THANKS*


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## BobCamp1 (May 15, 2002)

dlfl said:


> And what failed? TiVo(s) or attenuators?
> 
> One thing that could make an attenuator get hot (and it couldn't be the video signals) could be spurious DC coming in on the cable. A few volts on 75 ohms will make a small device like that hot. Why DC on the cable? I have no idea.


Then a DC block (a.k.a. series capacitor) for a type F connector would block that DC. $2 part. He can measure it first using a multimeter to see if there really is DC on that line. Note that it could be coming from the Tivo or something else on the cable system.

That DC could also be interfering with the Tivo's SNR measurement. Though I have no clue why the Tivo doesn't already have a DC block in its circuitry. Unless that's the part that failed. Capacitors (used for DC blocking) usually fail as a short, so a failure could allow the DC on the line.

It could be the RF section of his Tivo is broken. But I'd figure out if there's DC on the line before getting another Tivo.


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## dlfl (Jul 6, 2006)

dlfl said:


> ......
> One thing that could make an attenuator get hot (and it couldn't be the video signals) could be spurious DC coming in on the cable. A few volts on 75 ohms will make a small device like that hot. Why DC on the cable? I have no idea.





BobCamp1 said:


> Then a DC block (a.k.a. series capacitor) for a type F connector would block that DC. $2 part. He can measure it first using a multimeter to see if there really is DC on that line. Note that it could be coming from the Tivo or something else on the cable system.
> 
> That DC could also be interfering with the Tivo's SNR measurement. Though I have no clue why the Tivo doesn't already have a DC block in its circuitry. Unless that's the part that failed. Capacitors (used for DC blocking) usually fail as a short, so a failure could allow the DC on the line.
> 
> It could be the RF section of his Tivo is broken. But I'd figure out if there's DC on the line before getting another Tivo.


I realized later that AC (60 Hz power) on the cable could cause the same heating problem -- so check for that too. The desired cable signal is small and probably too high frequency to register on a multimeter, so if you see several volts of either AC or DC it's not right.


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## dlfl (Jul 6, 2006)

samccfl99 said:


> ....... I got a 3 and 6db attenuator from the comcast truck when it was in my complex. I have a Roamio Pro I got in 11-2013 and my SNR is 100% and 40-42db on all or most channels, as most people are reporting. Putting the 6db on, I only got 3db less and adding the 3db, I only got another 1db less. Why, is the first question .......


Attenuation should have little or no effect on SNR. SNR is by definition the ratio of signal power to noise power and both are reduced by the same factor by an attenuator. However it's widely suspected that the SNR number reported by TiVo is not a correctly computed SNR, and does vary (incorrectly) with attenuation. No one (outside TiVo at least) knows what exactly it does indicate -- but your results are not surprising.

BTW 42 dB SNR (that is, the bogus value reported by your TiVo) is generally regarded as an indicator of too hot a signal, definitely by TiVo support, and also by user experience. The most common symptom is pixelation but supposedly the continued running with too hot a signal can do permanent damage to the tuner.


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## samccfl99 (Sep 7, 2013)

dlfl said:


> -- but your results are not surprising.
> 
> BTW 42 dB SNR (that is, the bogus value reported by your TiVo) is generally regarded as an indicator of too hot a signal, definitely by TiVo support, and also by user experience. The most common symptom is pixelation but supposedly the continued running with too hot a signal can do permanent damage to the tuner.


Well you know that comcast thinks the levels as they calculate it are correct and as I said before, the XL4 ran within "tivo specs" on the same cable and cable card when I had them side by side during my transition. My SNR did go down when the attenuators first were put on, along with the SS. My RP does not really have any problems and it has been like this since I got it. WHY have they stopped working??? I missed the comcast truck today. Can't always wait for them to come out of the job they are on...LOL. I wanted to get new ones just to see if it would go back down again. I do not even know if it really matters. DOES IT???


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## krkaufman (Nov 25, 2003)

Jed1 said:


> The sad thing about all this is it is damaging to TiVo themselves because at the end of the day sending customers on wild goose chases only frustrates the TiVo customer. People telling the cable operators that the SNR is to high just results in them not taking TiVo seriously.


As I know you're aware, here's a great example thread demo'ing TiVo's wild goose chase approach:

http://tivocommunity.com/tivo-vb/showthread.php?t=533815

Months of problems owing to a mis-cabled tuning adapter, but with TiVo instructing the customer to fix their signal/SNR.


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## snerd (Jun 6, 2008)

dlfl said:


> Attenuation should have little or no effect on SNR. SNR is by definition the ratio of signal power to noise power and both are reduced by the same factor by an attenuator.


That is not quite right. SNR can be impacted by an attenuator in two different ways. Roughly speaking, the signal comes from the antenna or cable, and the noise comes from the tuner and amplifiers in the TiVo. A "noiseless" attenuator (which doesn't actually exist) would decrease the signal without changing the noise, so the SNR would degrade by exactly the dB rating of the attenuator.

There are conditions under which attenuation can have little effect of SNR, as you describe. For example, if the SNR at the input to the TiVo is 40dB and the signal has been amplified prior to reaching the TiVo, then the amount of noise added by the TiVo can be small compared to the noise added by stuff upstream from the TiVo.

Many electronic components (resistors, transistors, diodes) add noise. Attenuators are constructed from resistors, so a small amount of noise will be always be added when an attenuator is added to the system, but this is likely to be negligible compared the the decrease in signal level relative to the noise inherent in the TiVo.


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## foghorn2 (May 4, 2004)

Rent is too high, SNR is too high, O'llama is too high

forget Trump and Carson, we need this guy:


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## dlfl (Jul 6, 2006)

foghorn2 said:


> Rent is too high, SNR is too high, O'llama is too high
> 
> forget Trump and Carson, we need this guy:


Don't misquote him. The rent is too *damn* high!


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## dlfl (Jul 6, 2006)

snerd said:


> That is not quite right. SNR can be impacted by an attenuator in two different ways. Roughly speaking, the signal comes from the antenna or cable, and the noise comes from the tuner and amplifiers in the TiVo. A "noiseless" attenuator (which doesn't actually exist) would decrease the signal without changing the noise, so the SNR would degrade by exactly the dB rating of the attenuator.
> 
> There are conditions under which attenuation can have little effect of SNR, as you describe. For example, if the SNR at the input to the TiVo is 40dB and the signal has been amplified prior to reaching the TiVo, then the amount of noise added by the TiVo can be small compared to the noise added by stuff upstream from the TiVo.
> 
> Many electronic components (resistors, transistors, diodes) add noise. Attenuators are constructed from resistors, so a small amount of noise will be always be added when an attenuator is added to the system, but this is likely to be negligible compared the the decrease in signal level relative to the noise inherent in the TiVo.


I agree. I was assuming the dominant noise came in on the cable, rather than being generated in the TiVo circuitry itself. Do we know for a fact that the latter is the case? Of course it could be that both components are important.


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## Jed1 (Jun 18, 2013)

It took a while but I finally found the white paper that explains how SNR is done with analog signals and then how SNR (now MER) is done with digital signals.
It is important to note that a high MER number is good and a lower MER number is bad so the idea that you have to lower the MER number is going to lead to the TV signal to fail.
http://docsis.beckitrue.com/documents/cisco/CNR_SNR_MER_Cisco.pdf
The explanation starts on page 16:



> The SNR of a Demodulated Digital Signal: RxMER
> 
> The solution is to define a new quantity to represent the SNR of a digital baseband signal: receive
> modulation error ratio. RxMER is defined as the ratio of average constellation symbol power to
> ...





> More About Modulation Error Ratio
> 
> Modulation error ratio is digital complex baseband SNR - in fact, in the data world, the terms
> "SNR" and "MER" are often used interchangeably, adding to the confusion about SNR, especially
> ...





> In effect, MER is a measure of how "fuzzy" the symbol points of a constellation are. Table 4
> summarizes the approximate ES/N0 range that will support valid MER measurements for various
> DOCSIS modulation constellations. The two values in the table for the lower threshold correspond
> to ideal uncoded symbol error rate (SER) = 10-2 and 10-3, respectively. The upper threshold is a
> ...


Table 4 is on page 23 of the document.

As you can see by the chart and using best practices you want to keep the minimum threshold for MER (SNR) at least 36dB or more. Being at 40dB for MER is ideal. Since the 4 tuner Premieres, the Romio series, and the Bolt series are digital only then the SNR is actually the modulation error rate (MER).


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## dlfl (Jul 6, 2006)

Interesting technical detail but I assume you're not saying any of that explains why TiVo keeps saying things like


> SNR of 36db to 37db is to high and I need to get it down to around 32db.


(Quoted from the first post in this thread.)
Correct?

In other words, call it SNR or MER, how TiVo defines it is unknown, and what they say about it is inexplicable.


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## krkaufman (Nov 25, 2003)

dlfl said:


> Don't misquote him. The rent is too *damn* high!


And no need to get a weak tea imitation from SNL, go straight to the source...


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## Jed1 (Jun 18, 2013)

dlfl said:


> Interesting technical detail but I assume you're not saying any of that explains why TiVo keeps saying things like
> 
> (Quoted from the first post in this thread.)
> Correct?
> ...


Yes that is what TiVo tried to tell me but TiVo is absolutely wrong. There is only one engineered standard in North America for cable television. So in order for TiVo to be right then the entire cable TV industry is wrong and the $6000 cable spectrum analyzer I was using is junk.
One of the big problems with TiVo is it appears that the units are not reporting these numbers correctly. Secondly there is no such thing as a to high of an SNR/MER reading. The higher the number the better the quality of the signal and the lower the number the worse the quality of the signal is.
The article I just posted is a cable TV industry standard.
I have no idea how TiVo Support came up with this nonsense but they are using it as a one size fits all excuse to a number of problems people are having with their units. I was surprised that they said that the SNR on my Premiere units was to high as this is a complaint with the Roamio units.


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## snerd (Jun 6, 2008)

dlfl said:


> I agree. I was assuming the dominant noise came in on the cable, rather than being generated in the TiVo circuitry itself. Do we know for a fact that the latter is the case? Of course it could be that both components are important.


Good question that I don't have an answer for.

For OTA signals, I'm guessing that the TiVo would set the noise floor so that SNR would depend on the signal strength from the antenna. A good antenna can make a big difference, depending of the distance to the transmitter and the transmit power.


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## krkaufman (Nov 25, 2003)

This one's for you, Jed1; it has to be one of the funniest cases of "your SNR is too darn high" I've come across.

The punch line comes in post #5.

see: http://tivocommunity.com/tivo-vb/showthread.php?p=10522484#post10522484


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## snerd (Jun 6, 2008)

krkaufman said:


> This one's for you, Jed1; it has to be one of the funniest cases of "your SNR is too darn high" I've come across.
> 
> The punch line comes in post #5.
> 
> see: http://tivocommunity.com/tivo-vb/showthread.php?p=10522484#post10522484


Yup, apparently the SNR in the TiVo was so high that the OPs Mini couldn't boot up. Now *that* is too damn high!


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## Jed1 (Jun 18, 2013)

krkaufman said:


> This one's for you, Jed1; it has to be one of the funniest cases of "your SNR is too darn high" I've come across.
> 
> The punch line comes in post #5.
> 
> see: http://tivocommunity.com/tivo-vb/showthread.php?p=10522484#post10522484


I am wondering if the legalization of pot in Colorado has anything to do with this. Maybe the CSR's are the ones a little to "high" and not the SNR!


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## Jed1 (Jun 18, 2013)

I was reading a few tweets today for TiVo Support and I came across this juicy nugget.
https://support.tivo.com/articles/T...oamio-Series-Premiere-Series-and-Series3-DVRs
It is the trouble shooting procedure TiVo Support uses. The last call I had to them the CSR had me follow this to the T. 
Under checking signal lock and strength they had me start a recording on each tuner and I asked why and they stated this is to lock the tuners. I stated there is no need to do this as this is not what locks the tuner on the channel.

One of the major problems is there is no such thing as to high of an SNR. Also cable systems like to see the SNR reading at or above 36dB to guarantee that the signal will not have any issues.


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