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Upstream level fluctuations

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cablelady
Upstream level fluctuations

I have a node that is having a strange problem. All upstream levels are fluctuating constantly. These are anywhere from 5-10 db fluctuations. We have replaced all jumpers, splitters, combiners etc. in the headend. We have also changed lasers and fiber jumpers and took traces of the fiber from headend to node. All seem to be fine. The node type is an Antec LXR400 Gemini 870Mhz. I don't see any noise on the return path. I've isolated each leg off of the node also. The problem appears on all legs. If anyone has any idea I would be most grateful.

cmcaldas
Frequencies, levels, carrier

What do you use for a cmts? is it configured for frequency agility? if the return is fixed to be 32Mhz for example, what is the average modem transmit level and cmts receive level? constant carrier on the return. example a carrier at 41Mhz and 18Mhz at a termination point and monitor the carrier over time. does it too change by 5-10 dbmv? as for the change, does it just change or change from morning to evening? what area is the cable plant located? southern Florida or northern Maine?

~Carl

cablelady
We use a CASA Systems C2200.

We use a CASA Systems C2200. Not configured for frequency agility (although I have moved the return frequency with no joy). The average transmit level is 35-45 (on all other nodes, I can't get a good reading on this particular node right now). No constant carrier. The fluctuations happen every 5-10 minutes or so. I am in northern Ohio. The temperature is not fluctuating very much from day to night at this time of year, maybe 10-15 degrees. I am going to audit all grounding today (I already have at the node). Do you think that the grounding could cause this type of issue?

cmcaldas
doubt grounding issue

happening on all the cmts receiver ports or just one? if it's port 0 for example, if you swap it with port 1, does the problem stay with port 0 or does it move to port 1? what's the upstream channel width and modulation? are you doing upstream channel bonding as well?

cablelady
Not happening on all ports.

Not happening on all ports. Only one node area ( I tried different upstream ports on the CMTS the problem stays with that physical area). Channel width is 3200000 modulation is QPSK. No channel bonding. I only have approximately 18 cable modems off of this node.

cmcaldas
node power supply?

Know I'm drawing at straws here, but the issue stays with the same node. cmts has nothing to do with it since it's been ruled out. I'm thinking back to my old cable tech days and a bad ground at the power supply from the secondaries caused an issue as well. you've replaced the node and optical receiver, thinking you need to check the power source next.

cablelady
We switched the power feed

We switched the power feed from one leg to a different leg, so unless we have two bad power supplies...Although the power company has been re-spacing the pole lines in that area.

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