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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.

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:
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:
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?
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