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What cable modem signal levels are considered good ?

Cable modems often have a diagnostics web page that can help view the cable signal details (signal strength, upstream/downstream power levels, SNR, etc.). This information can be very useful in troubleshooting common connection issues. For Motorola/Arris cable modems, the stats page is at: For other models, refer to our broadband hardware database with over 3500 listed devices. You can use the values below as a guideline as to what good "signal levels" are.

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. You can also use a tap (directional coupler) to get a cleaner signal to the cable modem instead of a splitter.

Upstream Power (37dbmV to 55dbmV)
The lower this number is, the better. Above 55dB will most likely cause problems, over 57dB and you probably won't be able to connect. Ideally between 42 and 50dB. Lower than 42 may start introducing some packet loss (especially if you have much noise on the line). If you hit 58 the modem will likely drop the connection and resync.

Signal/Noise Ratio (SNR , >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. This is true for both the "Downstream SNR" and the "Upstream SNR", which may be different values. Typically, cable modems show the Downstream SNR, the Upsteram SNR can only be calculated at the remote end of the coax (usually at the node). Just remember that higher SNR means cleaner signal. A value well over 40 may mean you have too much power.

Note: Different brand modems may represent the information a bit differently, and may react a little different to exact power levels.

See also: Should I use a Cable Amplifier ?

  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?
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.
by anonymous - 2014-12-12 01:52
^ correct. 10 year tech. Up levels for us now should be no higher then 49. Down, closer to 0 the better but between+5 -8 is the range. Signal to noise 34 and up.
by anonymous - 2015-09-20 06:39
Why would you strat to see packet loss with a lower signal rate. The information is being sent the same way no mATTER WHAT. jUST BECAUSE THE RATE DROPS DOES NOT CHANGE THE WAY THE TRAFFIC GOES IN AND OUT. iTS JUST LESS OF A SIGNAL. sINCE YOU D=SAY THAT ONE WOULD ASSUME THAT THE HIGHER THE SIGNAL RATE THE BETTER AND FASTER THE PACKET??? i CAN SHOW YOU GREAT SIGNAL STRENGTHS AND LOTS OF PACKET LOSS. i DONT SEE THIS BEING TRUE AT ALL ACCORDING TO SIGNAL STRENGTH. There no way thet the signal strength effects packet loss. If im wrong then prove it. Im am IT tech and you have your hands full here. Especially with cable internet. Theres no such thing as slow speeds, wiat for it, as if there really was there would either be an outage of a very large area effected due to cable being a shared network. I get a lot of cals saying my speeds are slow on cable, Funny that thers probably 25 people on that node but the dude calling in thinks he the only one with the issue. Cable slow speeds on an individual bassis is either a software problem, or a hardware problem, unless the ISP is having issues Just my 2 cents!!!
by anonymous - 2015-10-12 13:09
Well, you are clearly no English professor, but here is why it matters IT guru. If you have too low of signal, your modem is going to try and find another carrier that may have better signal to transmit the data. If it is being overpowered with signal, the same thing will happen. Modems now a days are not dumb, but can sense when there is a problem happening. I hope to never accidently hire you O_o
by anonymous - 2015-12-07 17:32
90 % of speed problems as a phone tech for comcast was router related always do a direct connection to modem with a computer power down modem for at least a minute. After connected again run a new speed test. Modern routers are garbage if you don't know how to buy them by chipset.
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