What causes a bad SNR/How to fix a bad SNR?

AbyssUnderground · 01-08-2008, 00:55

Hello all,

About a month ago we had cable TV installed and ever since the SNR on the modem has been significantly lower than normal, causing random cut offs, mainly around 11pm - 6am period, never other times.

Downstream Receive Power Level : 5.53 dBmv
Downstream SNR : 28.11 dB
Upstream Transmit Power Level : 47.50 dBmv

Those are my levels at the moment. The SNR varies between 26dB and 32dB. Before the TV was installed, we had an SNR of 36dB+

If my broadband hasn't dropped out, you can see live SNR stats on http://m3ezw.no-ip.com:85/routerstats.htm

I have checked the cables and done my own trouble-shooting, and I have done the following:

Removed the TV cable
Removed the splitter
Tried with and without the attenuator on the modem
Replaced the connector on the end of the cable for the modem
Reseated all connectors in their plugs

None of those seemed to have any effect on the SNR level.

Does anyone have any clue as to what else could be causing this problem? It only started when we had the TV installed, yet the TV doesn't seem to have any effect on it (since it was tested with it removed).

If I need a technician out I take it that the call out would be free? I assumed I could correct this on my own but it seems not in this case.

Seems this is goodbye to 6 years flawless service from VM!

All help appreciated.

Thanks.

01-08-2008, 07:43

Quote:

Originally Posted by AbyssUnderground

Hello all,

About a month ago we had cable TV installed and ever since the SNR on the modem has been significantly lower than normal, causing random cut offs, mainly around 11pm - 6am period, never other times.

Downstream Receive Power Level : 5.53 dBmv
Downstream SNR : 28.11 dB
Upstream Transmit Power Level : 47.50 dBmv

Those are my levels at the moment. The SNR varies between 26dB and 32dB. Before the TV was installed, we had an SNR of 36dB+

If my broadband hasn't dropped out, you can see live SNR stats on http://m3ezw.no-ip.com:85/routerstats.htm

I have checked the cables and done my own trouble-shooting, and I have done the following:

Removed the TV cable
Removed the splitter
Tried with and without the attenuator on the modem
Replaced the connector on the end of the cable for the modem
Reseated all connectors in their plugs

None of those seemed to have any effect on the SNR level.

Does anyone have any clue as to what else could be causing this problem? It only started when we had the TV installed, yet the TV doesn't seem to have any effect on it (since it was tested with it removed).

If I need a technician out I take it that the call out would be free? I assumed I could correct this on my own but it seems not in this case.

Seems this is goodbye to 6 years flawless service from VM!

All help appreciated.

Thanks.

You need to call Tech Support to report your problem as the is no way that a user can adjust SNR, they will check you details and run some tests and probably book an engineer visit.

----------------------------------------------------------------------------
Tech Support is open 24/7 on the numbers below.

For help with your TV or Phone and for Broadband Technical Support:

Call Product Support/Faults on 151 from your Virgin Media Phone. It's absolutely free.

Or call 0845 454 1111 from any other phone line.

Kymmy · 01-08-2008, 10:38

SNR (Signal to Noise Ratio) is caused by one of three things..

Too low a signal (power needs jacking up at the box int he road)
Interference (again power needs raising to get over it)
Too high a power causing distortion and noise (The power needs to be lowered at the box unless it's already at low power, this is where the attenuator comes into play but it's hard to get right)

WhydoIneedatech is perfectly right in saying that a tech should be prought in to adjust it as it's ever so easy to think you've cured it only for a slight fluctuation to suddently make it worse. A tech who does his job correctly should get your levels mid-range so variance wither way will NOT effect the signal.

jonifen · 01-08-2008, 12:53

Apologies for hi-jacking this thread as it were, but as the topic is about SNR, what is an "optimal" SNR to have on a SACM?

For info, I only have 1x STB and 1x SACM connected.

AbyssUnderground · 01-08-2008, 16:23

Thanks, I think it is time to call out a technician then. I'll speak to my Dad and get him to call (being the account holder he has to).

01-08-2008, 17:24

Quote:

Originally Posted by jonifen

Apologies for hi-jacking this thread as it were, but as the topic is about SNR, what is an "optimal" SNR to have on a SACM?

For info, I only have 1x STB and 1x SACM connected.

Ideal level around 40dB not to high not to low.

eth01 · 01-08-2008, 17:25

Quote:

Originally Posted by whydoIneedatech

Ideal level around 40dbmv not to high not to low.

... (ignore, wrong thread)

01-08-2008, 17:28

Quote:

Originally Posted by eth01

... (ignore, wrong thread)

01-08-2008, 17:31

Quote:

Originally Posted by whydoIneedatech

Ideal level around 40dbmv not to high not to low.

Thats a signal level not an SNR?

Did you mean 40dB?
A very high SNR with an acceptable signal level would be best.

01-08-2008, 17:48

Quote:

Originally Posted by Losttheplot

Thats a signal level not an SNR?

Did you mean 40dB?
A very high SNR with an acceptable signal level would be best.

40dB is optimum and nicely in the middle, and yes I put mv in error.

eth01 · 01-08-2008, 17:48

Quote:

Originally Posted by whydoIneedatech

lol hiya mate

AbyssUnderground · 01-08-2008, 18:56

I just phoned up and the guy said because its working to call back when it wasn't! So I phoned back anyway and got another guy who has booked me an engineer because he knows there is a problem.

Amazing how some know how to do their job and some don't eh? The first guy said ex NTL was capable of working on an SNR down to 20dB! He might be right but its certainly not working that low for me.

I have an engineer booked for Monday anyhow so that should be fixed quickly. I just hope the engineer is not a "thickie" (sorry to all techies!) and actually knows what he's doing and listens to me when I tell him what is wrong instead of dismissing everything and claiming its fine!

I will have graphs to prove the SNR randomness and as of today I am going to record all the times it disconnects.

Lets hope it gets fixed!

jonifen · 01-08-2008, 21:09

Quote:

Originally Posted by whydoIneedatech

Ideal level around 40dB not to high not to low.

Thanks whydoIneedatech. That helps me, now to check if mine tallies up. It was 42 the other week, and was 33 last night... oddly enough, I've not knowingly had any problems.

Rep++

01-08-2008, 21:13

Quote:

Originally Posted by jonifen

Thanks whydoIneedatech. That helps me, now to check if mine tallies up. It was 42 the other week, and was 33 last night... oddly enough, I've not knowingly had any problems.

Rep++

Mine is 38dB at present and is rock solid.

Ignitionnet · 01-08-2008, 22:39

No 'high' limit to SNR for best performance though when it gets too high it's probably a misreading.

33dB+ is ok but higher the better.