Hi
I want to know what the output power of a cable modem in the coaxial port.
Please help me with your experience if having the modem only connected to the meter, I can know what its output power
This is to determine the status of the modem (good or bad) according to whether the output power is in the expected range.
Please help me with your comments
Hi
Any update on this query
you need to clarify your question and provide information.
example, I don't know what good levels are for modems and how to check them remotely without going to a customers' home with a rf meter to confirm, is that what your asking?
what cmts are you using?
what's the configuration for remote query?
what's in your modem file related to remote query?
what have you found to be the average modem levels?
my basic rules for modem levels are receive at 0 dbmv with a +/- 10 window. docsis spec is +/- 15, but when you get closer to that edge of that spec you tend to have intermittent de-registration. transmit levels should be above 35 and below 50 dbmv. you need to be above the noise floor and not transmit high enough the modem no longer bonds upstream. yes, some modems transmitting at 53 for example are bonded, but as summer temps go up the modems transmit at a higher level and eventually bonding will go from 4 Qams to just 1 Qam and then have issues staying online.
Hi
My intention is to test a modem that we have already used in a laboratory and measure what output power a modem should normally generate through the coaxial port, with the modem turned on and connected only to a meter, that is, test only the connected modem. to a meter in a test environment, do you know if there is a procedure to do this test
since you have a modem online, you need to send the cmts configuration. the modem file it downloads to get online, that you also need to send. in short, on the cmts you configure remote query with an snmp string like the word cable. in the modem file there's a section for snmp to control the modem and in there would match the word cable.
from that, the cmts or an snmp server can talk to the modem and do a get to show you things like power levels and downstream snr.
have good weekend
That will not work, unless your meter can act as a CMTS, when a modem is coming online if first locks on the downstream carrier, so your first hurdle would be your meter would need to generate a qam signal with the right modulation and the MDD (Mac Domain Descriptor) messages. The MDD lists all of the possible frequencies and upstream channel IDs the modem can connect back to the CMTS on. Finally, the modem ranges to the CMTS it will exchange a series of messages back and forth to the CMTS saying essentially can you hear me now, if the CMTS does not respond it increases its transmit power and tries again, this is repeated until the signal that reaches the CMTS at either 0 dB (or the value of power-adjust continue +/- from zero) or the modem cannot increase or decrease its power any more.
The best way to test the output power of the modem would be to create a 6ft cable plant (i.e. connected directly to the US/DS ports) connected to the CMTS with 45 dB of attenuation on it. With a known amount of attenuation you can configure those upstream ports with power-adjust continue of 0 dB, this should allow a 4 upstream modem to properly bond and your transmit power measured at the modem should be 45 dB (modem's web page can confirm) and the receive level at the CMTS should be 0 dB and the modem should be online. As mentioned previously on the downstream you will need attenuation too, the signal reaching the modem should be at 0 dB ideally.