What cable modem signal levels are considered good ?

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

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.

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.

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 =(

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.

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.

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

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.

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.

what is the min and max acceptable SNR, attenuation, voltage lavels in Unified Gateways 500 and unified gateways 200 ?

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?

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.

^ 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.

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!!!

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

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.

" 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!!!"

You clearly have [no] idea what you're talking about. Talking signal rates between comcast cable and Ethernet are two vastly different things. First, with ethernet, the higher the frequency, the faster and better the signal. However, this only holds true to a certain point (i believe). It also has to do with twists per inch. the higher the count of twists, the faster the transmission.

however, when it comes to cable, like the coaxial cable, it's the opposite. the higher the frequency, the more work the devices are doing to get the signal to the other end. the lower the signal, the less work. Everything about the coax affects how the transmission is done; power, distance, shelf life, etc. You get cross talk for ethernet cable, though i'm not entirely sure about coaxial ( i don't think so).

currently, my downstream signals are all above '651000000 hz'. I've got four. That's horrible. my upstreams are better, but only 3. I'm probably going to have a comcast guy come out and see if they can't re-calibrate those numbers. How can i back this claim up? Last night during an online game, i dropped out literally every 30 seconds. I couldn't play. My internet sucks because of these numbers. I'm paying for 10 Mbps and getting less than 3.

And just because you're an IT guy, doesn't mean didly. I'm an IT guy and i'm always learning new things within the IT field. And when I have to troubleshoot an issue, i learn and read as much as I can about the subject, including all the nitty gritty that i can understand. So a little piece of advice; don't assume you're right and we're wrong when the subject is comparing apples and oranges.

I've always had decent connections when the upstream power level is below 52. Anything higher and my signal starts to drop and re-sync. Nevermind the fact that the downstream is pretty well solid on all levels.

I don't get what's up with these people that work in a call center claiming to know everything. You're getting paid to read a script. Literally.

I've been programming for 15 years in about 6 different languages and I've also been working with networks for years.

Signal strength matters. Too high or too low, you're going to run into problems. It's all about finding that "sweet spot."

I want to get materials about FTTS test for cable modem

Just thought I would supplement what you said with additional info.Yes you can get cross talk to a degree with coax. Don't let anyone tell you different. Whenever there is a conducting metal being used for com purposes, you can get cross talk though not as extreme with telephone or Ethernet wires because of the extra layer of shielding and grounding used in decent quality coaxial. Although coaxial is shielded it can certainly pick up signals. Think ingress ,egress. I've seen it many times on the job whenever there has been a cut in the line and leakage detected.

Additionally there is the issue of bending radius which is very important. Many know of the importance of proper bending radius with Ethernet, but not so much on coaxial. Basically its not wise to bend beyond the recommended radius for good reasons, one of which being the stress on the conductor itself. Copper is malleable but only to a degree which is well documented. During my time as a installer and service tech I've ripped out thousands of feet of bad wiring installed improperly by techs who obviously were never educated on proper bending radius and how it affects the signal.

Also very importantly never run parallel with anything transmitting power. DC is generally ok but not AC. Code is no closer than 6 inches and for good reason. There is a thing called inductance which can not only cause issues with signal but be potentially deadly.Many techs understand when running underground not to run cable with power but then fail to do this in practice within a persons dwelling. I've seen cable run with house wiring many times and have had to reroute the wires safely away from power. The biggest issue with this is because traditionally cable techs weren't required to get low voltage licenses and don't understand electronic theory. There are set practices and codes that have to be observed when your a low voltage tech. Your work is inspected by Labor and Industries and if it fails -your in trouble or have to redo everything. Prior to becoming a service tech for TCI, then AT&T and then years later Comcast I was a low voltage tech doing security systems and a A/V tech prior to that and fully understood and abided by codes. When I stepped into the world of Broadband communications I was stunned to see just how badly they ignored theory and NEC codes. Not all of course but too many don't understand the reasons behind why certain codes are enforced.

I tried to educate my employer on certain issues, but that was a no win scenario. Many times they expected the tech to just dig up a UG bad cable line when in fact you have to get a underground utility locate first before digging and quite possibly exposing or damaging other lines such as power which is legally supposed to be way deeper than cable but many times I discovered was not. I also trained as a utility locator after leaving ATT for awhile and then coming back under Comcast.Once again I tried to warn and educate my employer that there are laws governing what we can or cannot not do in a given situation such as underground cable damage repair, but they just pushed the techs to risk their lives anyways. However once word got out because I informed my coworkers of reasons why I was saying no to the company many techs woke up and realized just how dangerous the situation was and many started to quote laws and code as a result.

Obviously I stirred up some trouble but I really didn't care. My coworkers safety came first and company profit last. Many customers sided with the techs once they realized how dangerous and foolish and greedy this was. It's not as if being a broadband tech really makes you wealthy. Many companies have frozen rapid advancement and many are stuck doing what they've been doing for years. Of course many leave and go to the phone companies to be paid more and have union protections. I'm glad I don't work for one of the most hated companies in America anymore, but I certainly feel for my former coworkers who are stuck doing the same thing day in and out with no opportunity for advancement, no real respect or recognition by their employer and way too much pressure and stress and then danger to top it off. Things would be so much better if Comcast was an employee owned company with technicians making decisions and not over greedy sales motivated bean counters who care nothing for their techs out risking their lives.

For one to try and determine what the best [upstream power] levels are for their cable modem using a service such as this, its rather moot. Comcast says 38-49, another provider says 45-55, another one would say, 33-60, and so on and so on. The reason is, no company (including different markets within the same company i.e. Comcast Denver and Comcast Chicago) is identical. The actual "sweet spot" for a cable modem to best work at is what we call "The X-Level", and it is system specific. Now someone will say, well if you said a modem can run at 60, why is it when I get to 56 I drop offline. Because, 56 won't work in your plant. Older optical nodes, older optical transport, etc. isn't designed to run that high. Also, you have to figure in the CMTS (Cable Modem Termination Service). An Arris C4 will run differently than an Arris E6000, which will be different from a CASA Systems, or a Blonder Tongue, or a Cisco UBR, etc. Also, if your modem is out of "company" specifications. They already know. Almost every provider has some sort of monitoring in place. Smaller companies might use something like BBX / Momentum. While Comcast uses Einstein, HIC tools and Scout Flux. Time Warner uses Node Slayer, I think Cox uses Drum. The last three, monitor every aspect of their plant. If a modem is out of spec, you're on the watch list. Also, some of the big guys, have gotten extremely anal retentive on watching levels. Comcast for instance, at this time, their automated system will not let the technician close and complete a job, if anything is out of spec.
But if you want generalized levels, that almost all providers can agree on, working well within their plant: Downstream Power Level -5 - +5 dB, Upstream power 42 - 47 dB, Upstream SNR 38-42, Downstream SNR 36-42.

Most cable modems are incapable of transmitting higher than 51 dBmV (upstream power). For example, I've read the specifications sheets for the Arris SB6183, SB6190 and TM822. They all have a maximum upstream power of 51 dBmV. If you need to boost your upstream power and your cable provider can't resolve the issue (besides suggesting you rewire your house), I highly recommend this return amplifier sold on Amazon: Electroline ERA 4100 Reverse Path Amplifier.

I'm looking at the status page of my SB6190 and it's showing 54dBmV for Upstream power.
Are you just shilling for that Amazon item? You're certainly mistaken about cable modem specs.

The SB6190 has different specifications. It's max upstream power is 56 dBmV (54 dBmV with 2 upstream channels, 50 dBmV with 3 or 4 upstream channels). See: https://www.dslreports.com/r0/download/2240221~a63e0a17e7c869c8bd5f02fae8096393/SB6190%20Data%20Sheet.pdf

are these good levels:
Downstream Bonded Channels
Channel Modulation Channel ID Frequency Power SNR
1 Locked QAM256 9 507000000 Hz 0.8 dBmV 43.3 dB 910448170 5 0
2 Locked QAM256 1 459000000 Hz 0.8 dBmV 43.7 dB 909266507 0 0
3 Locked QAM256 2 465000000 Hz 0.8 dBmV 43.6 dB 909271703 0 0
4 Locked QAM256 3 471000000 Hz 0.8 dBmV 43.7 dB 909275358 0 0
5 Locked QAM256 4 477000000 Hz 0.8 dBmV 43.5 dB 909277974 0 0
6 Locked QAM256 5 483000000 Hz 0.7 dBmV 43.4 dB 909281993 0 0
7 Locked QAM256 6 489000000 Hz 1.0 dBmV 43.7 dB 909286696 0 0
8 Locked QAM256 7 495000000 Hz 0.9 dBmV 43.4 dB 909288933 0 0
9 Locked QAM256 8 501000000 Hz 0.8 dBmV 43.3 dB 909296797 0 0
10 Locked QAM256 10 513000000 Hz 0.8 dBmV 43.3 dB 909300163 0 0
11 Locked QAM256 11 519000000 Hz 1.1 dBmV 43.4 dB 909304209 0 0
12 Locked QAM256 12 525000000 Hz 1.2 dBmV 43.5 dB 909307460 0 0
13 Locked QAM256 13 531000000 Hz 1.1 dBmV 43.4 dB 909312318 0 0
14 Locked QAM256 14 537000000 Hz 1.3 dBmV 43.3 dB 909315818 0 0
15 Locked QAM256 15 543000000 Hz 1.3 dBmV 43.4 dB 909319024 0 0
16 Locked QAM256 16 549000000 Hz 1.6 dBmV 43.5 dB 909323752 0 0
17 Locked QAM256 17 555000000 Hz 1.7 dBmV 43.5 dB 909329083 0 0
18 Locked QAM256 18 561000000 Hz 1.9 dBmV 43.5 dB 909333652 0 0
19 Locked QAM256 19 567000000 Hz 2.1 dBmV 43.6 dB 909337024 0 0
20 Locked QAM256 20 573000000 Hz 2.2 dBmV 43.5 dB 909340541 0 0
21 Locked QAM256 21 579000000 Hz 2.5 dBmV 43.6 dB 909344394 0 0
22 Locked QAM256 22 585000000 Hz 2.5 dBmV 43.4 dB 909348058 0 0
23 Locked QAM256 23 591000000 Hz 2.6 dBmV 43.6 dB 909352151 0 0
24 Locked QAM256 24 597000000 Hz 2.7 dBmV 43.7 dB 909356125 0 0
25 Locked QAM256 25 603000000 Hz 2.7 dBmV 43.5 dB 909359109 0 0
26 Locked QAM256 26 609000000 Hz 2.9 dBmV 43.6 dB 909363180 0 0
27 Locked QAM256 27 615000000 Hz 2.9 dBmV 43.7 dB 909366772 0 0
28 Locked QAM256 28 621000000 Hz 3.1 dBmV 43.6 dB 909371068 0 0
29 Locked QAM256 29 627000000 Hz 3.2 dBmV 43.7 dB 909372960 0 0
30 Locked QAM256 30 633000000 Hz 3.0 dBmV 43.4 dB 909378226 0 0
31 Locked QAM256 31 639000000 Hz 3.0 dBmV 43.6 dB 909378688 0 0
32 Locked QAM256 32 645000000 Hz 3.1 dBmV 43.7 dB 909380018 0 0
Upstream Bonded Channels
Channel Modulation Channel ID Frequency Power
1 Locked ATDMA 5 36500000 Hz 47.0 dBmV
2 Locked ATDMA 6 30100000 Hz 47.5 dBmV
3 Locked ATDMA 7 23700000 Hz 47.0 dBmV
4 Locked ATDMA 8 17300000 Hz 47.5 dBmV
5 Not Locked Unknown 0 0 Hz 0.0 dBmV
6 Not Locked Unknown 0 0 Hz 0.0 dBmV
7 Not Locked Unknown 0 0 Hz 0.0 dBmV
8 Not Locked Unknown 0 0 Hz 0.0 dBmV