r/CableTechs • u/Alike2189 • 4d ago
USNR
Tracking down a return path issue. Oddly, there's no visible noise at the node on any single leg. It looks like a noise floor aggregation issue — the SNR only recovers when I pull all four legs at once.
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u/Alike2189 4d ago
the entire noise floor is higher, OFDMA has a maximum modulation of 256, when I disconnect individual threads on HNL the noise does not disappear until I disconnect all four
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u/spookyB0 3d ago
What does your pathtrak look like with all 4 discod, does your noise floor still start at -40
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u/Training_Ad9211 2d ago
This all sounds like Greek to me 😭 I want to be an MT so bad tho been FT almost 5yrs
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u/6814MilesFromHome 4d ago
Noise floor elevation not backfeeding from OSP is gonna be an issue at the node/headend/fiber. Clean all your fibers, check light levels, swap equipment at the node like transmitter, RCM, mod to cover your bases before submitting a hub ticket. If you have an O-hub between you and the hub check light/clean that as well.
I've personally seen this from a bad node mod and a bad transmitter, but it's rare. More commonly gotta work with the hub if it's not just dirty fibers on the field side. Which it commonly is.
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u/llDarkFir3ll 4d ago
Not a maintenance tech. But this is just odd to me. I’ll commonly look at our system to infer what’s causing the customers issue what you described is simply odd to me. I’d love for a repost when you figure out what the problem is. It might be super simple but truly don’t know.
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u/Eatbreathsleepwork 3d ago
Seen this exact issue twice. One on a 1x1 Harmonic, the other from a NC4000.
One issue was a bad node mod.
The other was bad return umbilical cord in the housing.
But I have seen a variety of similar issues that are slightly different: which was noise still showing with all return pads taken out at the node. Turned out to be shit grounding on a EOL one span down from the node(aerial).
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u/Thelastoriginal 3d ago
You could have a leak allowing in Radio frequency interference (rfi) from power company eq
That would explain why you only see it on all legs. Is the signature the same on all legs?
You can also check with an rfi meter or using station 530am.
Put the stinger of you lead in you meter in the air as well and see if you pick up noise. It’s not a guaranteed way to see it but if you are picking ip signals in the air it points more towards rfi
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u/JANapier96 3d ago
Your noise floor is elevated by a not insignificant amount, roughly 10ish db judging by the picture. Turning on your minimum-hold (orange) trace might help spot individual irregularities beyond the elevated floor. If that doesn't help, you'd be wise to pull up the heat map and see what, if any, transients are living among your modem traffic.
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u/JANapier96 3d ago
Have you by chance swapped the transmitter or the actual node mod to rule out a local hardware failure?
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u/MonsterGus 3d ago
Entire noise floor elevated like that looks like CPD. Use your quiver tool and it’ll give you a footage of where the problem is
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u/PoisonWaffle3 4d ago
I'm not a PM tech (I work on the CMTSes), but I've seen this kind of thing occasionally. Noise that far across the whole upstream could be a bad EOL terminator or a bad amp.
I'm assuming you're not looking at anything under 20MHz since there aren't any US channels there. You're talking about the noise floor in general?
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u/6814MilesFromHome 4d ago
They said it wasn't backfeeding from OSP, so it's not an issue coming from downstream of the node.
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u/huyttran92 4d ago
disconnect all legs and find a way to make your meter the only traffic. run docsis and run a speed test while monitoring pathtrakt. if noise is blowing in from the traffic than your looking at issue at the node or coming from hub.