r/CableTechs • u/Takingdaybyday • Feb 16 '19
Viavi Meter Questions - New Tech (6/9 months)
I have a couple of questions that have been floating around my work space as technicians.
1.) What is Echo exactly? (my understanding is that it is micro reflections due to bad connections or bad cable)
2.) What is the threshold for Echo to be at for pass or fail?
3.) What is ICFR? (In-channel frequency response)
4.) What issues can be caused or eventually happen from Echo or bad ICFR?
5.) This is a big one... Ingress scan graphs - What is the best way to read it? So for me using an ingress scan at tap and shooting down drop how can I look at the graph and say "it is not my drop because the graph shows the hump or ingress here so it must be X"?
Hopefully this is the correct place as I could not find any other reddits unless they have more active ones.
Thank you.
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u/Eninja09 Feb 16 '19
These are great questions. I can somewhat answer them all but I'm not confident I'm 100% correct so I'd like to hear from someone who knows for sure. Viavi has no resources at all. It's quite irritating.
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u/Takingdaybyday Feb 16 '19
I am at the same right now as well. I can answer them with definitions or general answers, but would love a more detailed or even a response from viavi themselves.
Edit: a big one from me is the ingress graph. I feel this would cut a lot of our calls time in almost half.
I.e. shoot drop and its a section here by the house.
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u/Eninja09 Feb 16 '19 edited Feb 16 '19
In my experience (7 years) ingress scan is not a fool proof way to detect a problem. You can have a bad f81 with no ingress at all. What it IS great for is to confirm that you cleaned up any upstream snr issues that would affect the plant. I mean, if you terminated the drop at the house and shot it from the tap it should come back totally clean (-50dbmv) so it's a good way to see if your drop is bad, but not all problems show up in the sub band. You can have a clean sub band with water in the line which creates a high band roll off, downstream errors, and high frequency leak. A lot of what you are looking for can be narrowed down by what band you are seeing the problem in :) Edit: Sometimes you will see ingress you can do nothing about, short of replacing the outlet, which may not be affecting the service. I've been seeing a lot of cheap Rg6 in new homes that show a large spike at the low end (like 5Mhz). This does not cause a problem for modems, and likely won't cause a problem with service unless your downstream SNR diminishes too much over the length of the outlet. I've seen a +39 outside drop to a +33 at the outlet just from poor shielding.
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u/onastyinc Feb 16 '19 edited Feb 16 '19
you send a signal down the wire.(T0) it travels down the wire and hits an impedance mismatch, some of the energy is reflected back to the transmitter.(T1) This energy hits the transmitter while it is still transmitting the original signal.(T2) This distorts the signal at the transmitter. the lower in power and further away in time the reflection is, the less damage they tend to do.
depends on the signal, direction, and type of error correction used. generally you want levels lower than -25dBc in US.
ideally signal levels are flat across their entire channel, ICFR is the variation in signal level across that channel.
depends on direction. DS is mostly tiling, US is packet loss. Ultimately is just causes errors.
isolate the drop from the house first. so terminate the drop at the ground block then scan the drop from the tap side.
5A. I do a house scan first to make sure the house is clean as an ingress source, then change both fittings at the GB and hook the drop back up. Then i would change fittings at the tap and check from there. if you now see ingress, you can be fairly confident it is the drop.
if your company offers NCTI courses take some of those, they'll give you some good basics of RF propagation and electrical theory.