News Glossary of Terms FAQs Polls Cool Links SpeedGuide Teams SG Premium Services SG Gear Store
Registry Tweaks Broadband Tools Downloads/Patches Broadband Hardware SG Ports Database Security Default Passwords User Stories
Broadband Routers Wireless Firewalls / VPNs Software Hardware User Reviews
Broadband Security Editorials General User Articles Quick Reference
Broadband Forums General Discussions
Advertising Awards Link to us Server Statistics Helping SG About
The Broadband Guide
SG
search advanced
 Username:
 Password:
Register
 forgot your password?
 search
FAQs Categories:

What cable modem signal levels are considered good ?

Downstream Power (-15dbmV to +15dbmV)
Most modems are rated from -15dB to +15dB, however it's best to have it between +8dB and -8dB. Anything less or more than that and you may have quality issues. You can remove splitters on the line if you need to raise and clean up your signal level a bit.

Upstream Power (37dbmV to 55dbmV)
The lower this number is, the better. Above 55dB will most probably cause problems, over 57dB and you probably won't be able to connect. Ideally between 42 to 50dB

Signal/Noise Ratio (>30dB)
SNR is best over 30, (the higher the better, might work well with as low as 25 at times). Anything less than 25 will cause dropped connections, packet loss, slow transfers, etc.


  User Reviews/Comments:
    rate:
   avg:
by jstric2608 - 2008-02-09 15:50
The sweet spot for the upstream power is 48 to 52. If it gets to about 36 or 37 a Motorola 5100 will drop offline. Over 55 is a problem too.

Jim, data services tech
by helter - 2008-02-10 09:49
Wouldn\'t that be 38 to 52 then? ;)

Yeah, 35 and lower is pretty much a node problem in my FFO.
51 is our cutoff for upstream though for installs, it will run at 52, but on an install you better have a sub with 3 daisy chained splitters, etc if you leave it like that without a escalated call to adjust the plant if there is no other fix available.


Dan the cable man. C o m c a s t.
by anonymous - 2008-10-07 00:23
You gotta be a little careful about how to read the levels, as different brands of modems are a little different.

The Motorola's are a good average equipment, they are widely deployed and seem to sit about the middle in terms of where their 'sweet spot' is, relatively.

Generally your upstream should be in the low to mid 40's minimum, as lower than this could start introducing some packet loss (especially if you have much noise on the line) and is best if it doesn't not get above the low 50's. 55 is getting kinda iffy, and most of the time if you hit 58 the modem will start dropping the connection and re-synching.

The downstream receive should ideally be 0, but is almost always a little towards either side. Within +/- 10 is best but even +/- 15 isn't usually a big deal.

The modem status will show the downstream SNr (signal to noise ratio) which usually should be above 30, mid to upper 30's is good, over 30 usually means you've got too much power anyhow, and under the 25-30 range you're gonna start losing packets.

In all cases, filters & pads on the line will affect your signals, but the more stable they are the better. A rock-solid upstream of 57 will run better than one that varies between 40 and 50 rapidly.

If you're wondering, the upstream SNR can only be calculated at the remote end of the coax, usually at the node, but ideally it will also be stable in the low to mid 30's.
by anonymous - 2009-01-06 16:05
I have good cable modem signals, but my upstream is way to high its 61, any of u techs out there have a fix for it? Because ive been told thats why my internet is so slow =(
by Philip - 2009-01-08 07:25
Your signal levels are not ok if your upstream power is 61, you should call your cable company and have them work on the line to fix it.
by Joe - 2009-04-14 12:41
This is all good, but how do you get the current ratings of your signal? I have looked at the connection on the computer and this info is not listed.
by Philip - 2009-04-14 13:20
Many current cable modems have a web interface showing signal levels. It is often as easy as pointing your web browser to the IP address of your cable modem.

For a list of common modems and their default IPs, check our hardware database: http://www.speedguide.net/broadband-list.php
by anonymous - 2011-10-14 15:07
will 35 power cause my internet to come in and out, and be very slow when it is working? I am getting about .50 to 2.07 download mbps right now.
by JOGJAMEDIANET - 2012-05-21 13:18
On my Motorola SB5100i at midnight till morning SNR is 30 dB, it's no more bandwidth. If SNR reach below 29 dB, modem is disconnected. At daytime is the best, SNR reach above 35 dB.
by Pavithra - 2013-12-18 04:19
what is the min and max acceptable SNR, attenuation, voltage lavels in Unified Gateways 500 and unified gateways 200 ?
by geek1ab - 2014-01-18 13:42
I have an account with Comcast and have recently been experiencing frequent slowdowns and disconnects. My modem is a fairly new Cisco DPC3008. It has 8 downstream and 4 upstream channels. The power level on all downstream appears to be good (1.5-3.3). However, the power level on 1 of the upstream is 0. Also, the signal to noise ratio is 0 on one of the downstream channels (between 38.3 and 39.0 on all others.) Is my modem broken?
by anonymous - 2014-11-13 23:12
I know, you asked the question many months ago, but just in case anybody else has a similar question. DOCSIS 3.0 can use eight downstream channels. This does not mean your cable provider is using all eight. If they only run seven, you will only see seven and the eighth will show as zeros.

As far as upstream goes, it's how much signal your modem has to pump out to reach the head end through the cable system. If there is a lot of amplification on the return, your upstream will be low, like in the 30's. That's not good because at the lower limit, most cable modems don't do too well. I could go into a technical discussion of why this is, but suffice it to say, you want your transmit or upstream to be somewhere between 42-48.

It was previously said in this thread that the upstream level could only be read at the head end. This is not/has never been true about the transmit levels, but is commonly thought to be so, even by people who SHOULD know better. Signal to Noise on the upstream the only reading that must be taken at the head end. The head end (and CMTS) is only able to measure the levels it is receiving. When a cable modem starts to lock onto an upstream, it adjusts it's levels until the head end is receiving at close to 0. When return levels are within range, the head end tells the cable modem it's good and the number you see on your diagnostic screen is the modem telling you how much amplification it is using to achieve this. The reading cannot be taken until the connection is made, but it is still from the modem. Upstream signal to noise, however, is the S/N ratio at the other end, so THAT cannot be determined by the modem, itself and is reported by CMTS to the modem. With signal to noise ratios, the higher the better. I've been working with these since 2000, btw.
comment top