VDSL crosstalk, no vectoring

arctan

any ideas how to combat vdsl xtalk on a non vectored line, xtalk from other non vectored line

fat-tony

How do you know it's crosstalk? I would think that you should report issue to ISP/eircom for investigation and resolution rather than resolving it yourself.

lucernarian

arctan wrote: »

any ideas how to combat vdsl xtalk on a non vectored line, xtalk from other non vectored line

Would changing one of the lines to a different pair make a difference?

arctan

you can see the streams on a bare line (just the copper pair, nothing either end), on a spectrum analyser

fat-tony

More info please! Is this inside your house? If you know how to use a spectrum analyser you probably know the reasons why crosstalk occurs and how to mitigate - physical separation of cable pairs, proper twistrate. What effect is this crosstalk having on actual modem performance?

arctan

200, to 100 , to 50 pair cable, approx 200 m section in total (2 joints in route)

changing pairs hasn't worked, capacitive balance fine (not split), cable section is testing fine insulation resistance wise

crosstalk is suspected for intemittent sync issue

lucernarian

Crosstalk should be a quasi-fixed constant. Unless the offending line happens to serve another customer who switches on and off their modem regularly.

I'd wonder if crosstalk is the cause if sync issue is intermittent. I'm prone to suspecting electromagnetic interference given the number of things found in modern homes that could cause sync loss.



Am I right in saying that the other customer should be equally affected if crosstalk is the issue? Is it possible to check if the problem exists somewhere else in the vicinity?

arctan

im more inclined to the rfi reason myself, although can't find any sort of sync loss pattern and had a sweep of the area with an RF meter and nothing showed up really

cross talk signal on the completely bare copper line is circa 40- 50% the amplitude of the signal that is to go down the line, so it may be significant enough to disrupt sync...

fat-tony

@arctan - this thread is quite surreal - normally technical help requests come from home users, but you seem to be dealing with an actual VDSL install such as would be done by an eircom tech. I'm struggling with the context

lucernarian

50% of the amplitude of the original signal in another cable is not even physically possible due to induction alone, to the best of my understanding of these things. I.e. it would require some kind of resistive breakdown aka short circuit.

I'm at a loss to explain this. I assume the spectrum analyser has some kind of scale setting. Hate to patronise you but was the machine definitely on the right scale?

arctan

sorry, used to explaining this scenario to people who use the spectrum analyser visually ... on a dBm scale

tx signal is circa -30 to -20 dBm

where signal on bare cable (I've tried two pairs both similar) is around -70 to sometimes -50 dBm

at a loss myself, especially as everyone else is working fine (another reason I suspect a sporadic rfi source)

ED E

I suspect you're KN Networks staff or an Eircom FST OP, no other reason to be asking this. Very interesting all the same.

arctan

I'm actually neither