55 or 65 dBmV max?
Bookmark this page:
 Yahoo!
 Google
 Windows Live
 del.icio.us
 digg
 Netscape
|
|
||||||||||||||||||||||||||||
|
Posted by Winston on September 5, 2006, 8:58 pm
Please log in for more thread options I've always thought 55 dBmV was the maximum upstream power level cable modems are capable of. Tonight while speaking to a Time Warner / Road Runner tech. support guy, he said he'd seen numbers up to 65 and that his DOCSIS monitoring software showed anything up to 58 as green, up to 62 as yellow, and above 62 as red (I may be off by 1 in those cutoffs, but roughly that, and all the numbers were >55).
Anyone know what the story is? Was I wrong about 55 dBmV being the limit? Are newer cable modems capable of higher upstream power levels? Are numbers >55 some quirk of the DOCSIS monitoring software?
Thanks in advance, -WBE | ||||||||||||||||||||||||||||
|
Posted by Ed Nielsen on September 6, 2006, 10:43 am
Please log in for more thread options You are correct. As specified by DOCSIS, +55dBmV is the max transmit power at which cable modems must work. That does not mean that they won't work above 55. Most will keep on ticking at a bit higher than that, but anything above +55 is pretty much just a safety margin. CIAO! Ed N. Winston wrote: > I've always thought 55 dBmV was the maximum upstream power level cable
> modems are capable of. Tonight while speaking to a Time Warner / Road > Runner tech. support guy, he said he'd seen numbers up to 65 and that > his DOCSIS monitoring software showed anything up to 58 as green, up to > 62 as yellow, and above 62 as red (I may be off by 1 in those cutoffs, > but roughly that, and all the numbers were >55). > > Anyone know what the story is? Was I wrong about 55 dBmV being the limit? > Are newer cable modems capable of higher upstream power levels? > Are numbers >55 some quirk of the DOCSIS monitoring software? > > Thanks in advance, > -WBE | ||||||||||||||||||||||||||||
|
Posted by Winston on September 8, 2006, 8:46 pm
Please log in for more thread options
I posted: # I've always thought 55 dBmV was the maximum upstream power level cable # modems are capable of. Tonight while speaking to a Time Warner / Road # Runner tech. support guy, he said he'd seen numbers up to 65 and that # his DOCSIS monitoring software showed anything up to 58 as green, up to # 62 as yellow, and above 62 as red (I may be off by 1 in those cutoffs, # but roughly that, and all the numbers were >55).
#
# Anyone know what the story is? Was I wrong about 55 dBmV being the # limit? Are newer cable modems capable of higher upstream power levels? # Are numbers >55 some quirk of the DOCSIS monitoring software?
> You are correct. As specified by DOCSIS, +55dBmV is the max transmit
> power at which cable modems must work. That does not mean that they > won't work above 55. Most will keep on ticking at a bit higher than > that, but anything above +55 is pretty much just a safety margin. So then you're saying that there do exist cable modems that can send above +55dBmV? In that case I was wrong, since my impression was that +55dBmV was the limit of what cable modems *can* send. For example, I never saw my Motorola Surfboard 4100 go above +55. Maybe that's just a 4100 limitation? Thanks in advance (again), -WBE | ||||||||||||||||||||||||||||
|
Posted by Andrew Rossmann on September 9, 2006, 10:47 am
Please log in for more thread options
@ubeblock.psr.com.invalid (Winston) says... > So then you're saying that there do exist cable modems that can send
> above +55dBmV? In that case I was wrong, since my impression was that > +55dBmV was the limit of what cable modems *can* send. For example, I > never saw my Motorola Surfboard 4100 go above +55. Maybe that's just > a 4100 limitation? When I was having problems once, I saw my SB5120 trying to transmit at 61dB (my normal is around 45-51). May cable box (Motorola DCT-6412) is transmitting at 60dB, but OnDemand works, so it is working. -- If there is a no_junk in my address, please REMOVE it before replying! All junk mail senders will be prosecuted to the fullest extent of the law!! http://home.att.net/~andyross | ||||||||||||||||||||||||||||
|
Posted by Eric on September 9, 2006, 10:10 am
Please log in for more thread options
Ed Nielsen wrote: > You are correct. As specified by DOCSIS, +55dBmV is the max transmit
> power at which cable modems must work. That does not mean that they > won't work above 55. Most will keep on ticking at a bit higher than > that, but anything above +55 is pretty much just a safety margin. > > > CIAO! > > Ed N. > > Winston wrote: > > I've always thought 55 dBmV was the maximum upstream power level cable
> > modems are capable of. Tonight while speaking to a Time Warner / Road > > Runner tech. support guy, he said he'd seen numbers up to 65 and that > > his DOCSIS monitoring software showed anything up to 58 as green, up to > > 62 as yellow, and above 62 as red (I may be off by 1 in those cutoffs, > > but roughly that, and all the numbers were >55). > > > > Anyone know what the story is? Was I wrong about 55 dBmV being the limit? > > Are newer cable modems capable of higher upstream power levels? > > Are numbers >55 some quirk of the DOCSIS monitoring software? > > > > Thanks in advance, > > -WBE Well, the DOCSIS 1.0 spec stated that a modem must transmit from +8dB to +58dB. I haven't really checked transmit levels in the later specs, so I can't address any changes they may have made. Manufacturers were allowed to have their modems transmit higher levels if they wanted, but the spec says 8-58dB. If the upstream bandwidth is 1.6MHz, QPSK modulation, modems will be able to transmit at a slightly higher level. Some modems show this number, some just show the same level no matter what the modulation. Moving the 3.2MHz QPSK will cost you 3dB, and 16QAM will cost another 3dB. Again, depending on the modem, it may or may not show a change, and the CMTS may take the power level change into account and not need to make the modems transmit higher (Cisco uBRs know that the levels are different, Arris Pizza boxes did not, IIRC). At any rate, your cable tech needs to go through the class again. Any modem transmitting higher than about 55dB should be investigated. Most system designs plan for modem (and STB) transmit levels to be in the mid to upper 40's range. | ||||||||||||||||||||||||||||
| Similar Threads | Posted |
| 55 or 65 dBmV max? | September 5, 2006, 8:58 pm |