Hello Experts
I am a bit new to the cable industry of which my friend is more advance. The problem that is being experienced is that he has a Docsis 1 CMTS with 50 modems connected and working and he purchase a Docsis 2 CMTS system of which he wants to have both on the same network. One has a 357MHz frequency while the other has a 459MHz frequency.
Question, can you use a splitter and merge the two upstreams (ctms1 and cmts2)? when the upstream is connected to the Docsis 1 CMTS alone the upstream SNR is 30.9DB; however when he tries to merge both upstreams, the upstream SNR drops to 15.2 DB which is way too low, looking for over 30DB for proper functionality.
What solution or advise you can give. I thank you in advance.
Docsis 2 - Arris C3
Docsis 1 - Cadant
Grato
Hi,
In theory it is possible, as long as you configure unique downstream and upstream frequencies for each CMTS.
In your case, it seems that both CMTS are configured with the same upstream frequency. As one CMTS doesn´t know what is going on with the other, any upstream transmission from modems connected to a CMTS will look like noise to the other.
If you adjust that, it probably will solve your problem.
Hope it helps.
MS
Thanks Msarmento
I realize that both CMTS upstream was 26.75MHz and 28 MHz respectively and that was creating noise. I asked the technician to change the frequency on the new CMTS to 32 MHz I then got two modems to lock on Amplifier 1, however when I went to Amplifier 2, the modems were not locking, its finding downstream but not upstream. As I mention I am new to the business, so we turn down the amps by 14 dB then it locked on the new CMTS but throughs off the others modems that were locking on the existing CMTS. When I checked the server log on the new CMTS, it is showing that my upstream SNR is 16.5 dB while downstream is 32.5 dB.
It seems that the more modems is connected the upstream values goes lower, what could be wrong? Is it the CMTS (bought used)? or is it the the configuration, should we change the upstream frequency of power level from 32 Mhz to about 34 Mhz and the power level from 17 to about 20. Please advise. Thanks.
Hi,
kind of guessing since I don´t know your exact configuration.
Things to check:
1) What is your channel width? If it is 3.2MHz, moving to 32MHz is ok, but if it is 6.4MHz, you are still in conflict. If your return path is 42MHz, use the higher frequencies, less ingress on that region. Remember that you are configuring the CENTER frequency of the channel on the CMTS.
2) Configure both CMTS with the same Input Power Level of the original CMTS for the return path. If it was working before, there is no need to change. Once you are (probably) splitting the return between the original CMTS and the new one, max additional loss will be 3dB.
Regards,
MS