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Cable modem signal levels

What do signal levels and SNR mean ?
2003.06.24 08:45 by evrensen


What is a good "Signal Level" ? What is "Upstream SNR" ? What is a good signal strength ? If you want to know the answers to those and other similar questions, read on.

The basic information about your particular brand of modem can probably be found at the manufacturer's website... The most taled about issue when having problems, and the first thing to analyze, is the status of the signal to your cable modem, so what does it mean ?

On your cable modem manufacturer's page you might find terms such as: downstream SNR (signal to noise ratio), downstream power level, upstream SNR and upstream power level. Here's what all those mean, and a general guideline of what constitutes a problem:

Downstream SNR shows the strength of the signal to your cable modem as compared to the noise on the line (signal/noise). If the noise level increases the SNR value decreases. So, then high levels are good for the SNR. This number should be at 30 or more. If the SNR goes below 30 than you will probably start to experience some  problems, such as intermittent connection, packet loss, etc.

Downstream Power shows the power of the signal your cable modem is getting. The level of the downstream power should be -15 to 15 dB according to most manufacturers' specs... However, it is best for that level to be in the -8 to 8 range.

Upstream SNR shows how much signal the head end is getting from your cable modem, compared to the noise level. "Head End" refers to the point of reference that is the central point of the local network of your service provider. Anything above 29 is good. Just like the download SNR if the noise level increases the upstream SNR decreases.

Upstream Power shows the level of the signal from the cable modem to the provider. This number should be lower than 55dB. The lower the number, the better your connection.

All those numbers can aid in determining many potential problems with your cable modem connection...

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by anonymous - 2007.02.03 13:10
Pretty good technical info but how can all the signal levels be measured without special equipment? I have a new cable modem with service from time warner cable and have not had reliable connectivity yet. I get a popup balloon with win XP in the lower right corner of the screen advising me of limited connectivity at least once per 15 seconds or so. Very annoying.
by Philip - 2007.02.04 09:29
Many modems have a private administration IP address that's accessible through a browser. You can generally see the signal levels in the admin pages.

For example, if you have a Motorola 5000/5120 cable modem, the address you'd type in your browser is: http://192.168.100.1

For more information on other cable modems, check our broadband hardware database: http://www.speedguide.net/broadband.php
by anonymous - 2009.05.13 20:36
Hey some updated info for all of you, if you have Comcast and Comcast in your area is offering docsis 3 signals is going to be a lot pickier. Comcast says all modem must meet following specs or your modem may reset or give you limited or no connectivity:
Signal to Noise Ratio (SNR): 32dB-50dB
Power Level: -5 to 5
Upstream Power: 32dBmV-50dBmV
All levels should be within the ranges
If you are not sure if you are in a docsis 3 area call Comcast Or go on their web site and see if they offer any speeds over 20 mb in your area.
by frustrated - 2009.11.18 10:43
I also have Time Warner's cable modem and service, and I too have constant problems - I've complained more than once but all they do is tell me they're sorry and send me another month's bill... I STILL have to reboot their modem 4-5 times per day when I get kicked offline. How can those of us with Time-Warner service stop the headaches they ignore?
by anonymous - 2009.12.09 10:42
Also having verrry sloooowww experiences with TWC...
by mike - 2010.01.23 22:34
what is your signal entering the house? have t/w check . If you are using wireless your problem could be with modem or internal wiring, especialy if it is amped. 1st guess is bad signal from pole or pedestal.
by anonymous - 2010.04.11 01:19
If you are having Internet connectivity issues due to RF-signals, in addition to having your indoor wiring having checked and/or replaced, make sure that they replace the connectors and cables in their (cable company's) distributor box outside the building. In my case I knew the problem was being caused mainly there (because it would always go away when I went downstairs and wiggled the connectors) but they are always reluctant to accept it, since it's their responsibility to maintain it and do so free of charge. The problem can also be hard to detect if it's an interminent one (mostly good signal but sometimes bad signal) as in my case. So, make sure to have those cable and connectors in the cable-company-owned distributor box replaced as well.
by anonymous - 2010.04.16 15:57
Actually It is up to them to provide free service if the problem is anything outside your house and any of their equiment, but if you have bad wires in your own house they can charge you a fee for rewiring the inside to your house. A lot of companies will run a decated line from the cable or phone box on your house in through the outside of your house to the room you have your modem in. And sometimes run a new line from the pole to your house and then to the room This will give you a deditated line to your modem giving you the best signal you can get.

Anyway regardless most techs will try and fix the problem without charging you, if they are a good tech anyway. Some companies even charge for running a new decated line around the outside of your house in to your computer modem room. But if it is outside or on their side it should be free if it is inside and on your side like bad/old cable/phone lines/jacks there may be a fee to fix these problems.
by anonymous - 2010.05.30 08:50
Most modems have a page you can access by typing in am ip address just like your routers it will show you most of the signal levels. 192.168.100.1 this is the ip for a Motorola surfboard, most of the time your computer needs to be connected directly to the modem without a router in the mix. The only signal level it will not show is upstream SNR
by anonymous - 2010.09.27 12:47
this following is direct from motorola.

The cable modem should be placed in an area where it is closest to the cable tap and one should make effort to avoid additional connections. connection that include splices and additional taps/splitters. also it should be without the presence of an amplifier.

I had my modem put on a fixed (separated) line into the house no splitters no amps no more than 125 feet of cable i used commscope3.0ghz rg6 swept quadshield with messenger cable to allow for the headroom. Cox did not like the idea of using my cable but they did it anyways, shortly after alot of problems just seemed to go away.
by anonymous - 2011.08.01 17:12
Correction to the article

Power levels are given as ratio to a reference level (1 mV or 1 V), the unit of a power level is dBmV or dBV.

For the levels in the article the unit is dBmV.
-15dBmV to 15 dBmV (for the downlink level) are 45 to 75 dBV.
by anonymous - 2011.09.29 22:04
This information really helped me repairing my internetconnection myself... I had suddenly unstable internet connection and the internetprovider kept telling me the signal to the cablemodem was ok...

Finally i got here in search of explaination for the data in my cablemodem i found via another website to acces it and found out that the signal was pretty weak instead: Upstream power was significant more than 55db...

I soldered the cablemodem directly to the main cable that enters the house, without any splitters (i don't use cable tv).

Now i got very good signal levels and i can use my full internetspeed now of 14Mb/sec (120Mbps)... ;)

Thanks alot for the information!

Greetings from the Netherlands
by anonymous - 2012.01.18 17:25
Comcast doesn't know what they are talking about. Its pretty bad when I call with a problem and I have to tell them how to fix it. I would fix it myself but I don't have access to the CMTS's and other headend equipment. As a DOCSIS engineer I can't believe how under-educated comcast employees are in the DOCSIS arena!
by anonymous - 2012.05.10 13:48
How to access Webstar DPC2100R2 hidden pages
If you have Time Warner Cable and perhaps other cable operators as well that use Webstar DPC 2100 modems, and you happen to have one of these modems, no doubt you've become frustrated when you go to check the modem log if troubleshooting a connection issue, only to be greeted with the web page that says that this feature is not enabled. You however can still get at the information you're looking for. I don't understand why these diagnostics pages have to be hidden from us, especially when other modems show us the info we want with no issues. But here are the steps to gain access to the other diagnostics pages on a webstar DPC2100 modem.
First, go to http://192.168.100.1/_aslvl.asp and change the access level from 1 to 2. Enter the password of W2402 and hit submit. You should then be able to access the signal and logs pages with no issues. I've however noticed that the access level after maybe about a minute or so reverts back to level 1, so if while browsing the page, if it refreshes and it suddenly says this feature is unavailable again, just repeat the steps above. Like I said, I wish I knew why so much effort is made to keep us from truly seeing what's wrong with our connections. There's no harm in viewing this info ya know. So there's my hopefully useful tip for today.
by Gordon - 2012.07.15 14:47
Thanks anonymous on 5/10/12! I've had that modem for years, and was always irritated that I couldn't look at more information. I never knew there was an easy way to view it. Awesome!
by Joe in NY - 2013.01.09 15:48
ATTENTION ALL TWC CUSTOMERS!!!! i am too with TWC and i called them up to check my signal. well tried to call. better off using the online chat. anyway the next two guys came to check the signal. they analyzed it and said i needed a booster and installed one for FREE because i was a TWC customer. Internet and phone became much better. then i purchased a Motorola SURFBoard SB6121 Modem. it got rid of the $4 monthly fee and INCREASED MY INTERENET SPEEDS! so get them to check your signal and them purchase the modem from above and your internet will FLY! i hoped this helped. good luck to all!
by Jesse - 2013.05.13 23:31
Information was very helpful. I had issue galore with TWC. I just do not want to bother with their technicians. One of the main reasons I got a Surfboard 6141 was take advantage of 50mps and he diagnostics. Since I purchased this modem I was able to identify a bad cable run and fix it myself.
by domo the gamemaster - 2013.07.24 14:54
best way to get TWC to fix stuff is call every time your internet goes out. i called 2-4 times a day and they finally came out and reduced the upstream power levels and gave me a new modem because the high levels killed the modem.
by anonymous - 2014.05.03 19:12
Same issues here with TWC. They never fix the problem and give credit.
by mauricioqsjr - 2014.05.20 12:07
Very good, thanks from Brazil!
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