WITHOUT ripping out the drop wire that runs through.

I feel a time related charge coming on.

In reply to a post by Zarjaz:

A damaged cable will give you audible noise, from the resulting earth and battery contacts, low insulation, HR's etc.

We've even had experience of that. The line sometimes clicks during voice calls. Not enough to annoy, but enough to know it is still there. One time last year though, it became bad enough to report, with the following symptoms (pulled off the ticket to Plusnet)

- Clicks on the line during a conversation, with no adverse consequence
- Clicks on the line during a conversation that make the exchange act like a recall button was pressed, putting call on hold
- No dial tone when picking handset up to make outgoing call
- No ringing indication from the phone for an incoming call (the caller hears ringtone)
- Incoming call cannot be picked up (handset being lifted while caller hears ringtone)
- When dialtone is not being given, a white noise can sometimes be heard - a very faint, crackly sound.

The VDSL2 signal survived all of those - it stayed 80/20, with no DLM intervention, and no change to the error rates.

[It ended with no fault found, and has reverted down to just the first symptom]

I wonder if MHC is correct - that certain problems can cause adverse effects on the way the filter works ... and I wonder if it matter what the distance is between problem and filter. That is, whether a line problem near the cabinet would have more effect than one near the exchange, or vice-versa.

I wonder if the OP has unlocked his modem to look at attainable rates ? The audible noise could well be from a mullered E-side, but his drop in sync rate is going to be something D-side related, cross talk or some such.

It would be good if true, but a little late now - there will be no "before" picture to compare against.

In reply to a post by Zarjaz:

WITHOUT ripping out the drop wire that runs through.

I feel a time related charge coming on.

So far so good ... and the span is over 45m across a main road, river and garden!

Removing the Terminating Resistor, creating an Open Circuit, would result in a Standing Wave being produced by reflection from that open end.

The Voltage doubles; and if you follow the Standing Wave back towards the Source, the voltage drops to Zero at one-quarter wavelength back, rising to a similar but opposite phase peak, half-a-wavelength back, passing through zero at 3/4s wavelength and rising again to being in phase at one wavelength back.

Similar occurs with a Short Circuit in place of the Terminating Resistor/Load; but with the zero-volts point being at the short, rising to twice the supply voltage, at 1/4 wavelength back etc.

As you surmise, the effects on operations is similar with a Short Circuit - the Ethernet will not work.

I taught this many times; but had not seen it in practice until about 1992, when I obtained a TDR (Time Domain Reflectometer) for testing Thin and Thick Ethernet installations, amongst others.

Connecting an Oscilloscope to the TDR, I was able to demonstrate all three conditions, Properly Terminated, Open Circuit and Short Circuit, to my colleagues, including the differing phasing of the Short and Open circuits.

The TDR would also measure the time delay for reflections, converting these to a "Distance to Fault" which was accurate to about 1 foot/30 centimeters. Close enough for fault finding.

The TDR could also be used on other cable types, such as mains, twisted pair etc.

A simple description of the TDR would be a"Pocket Radar Set"; and it was about the same size as a typical digital voltmeter.

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Regarding the Doubling of the Voltage, if you have done any electrical loading work, the maximum power in the load occurs when it matches the impedance/resistance of the Source etc; thus the observed voltage in a simple unregulated DC circuit will show the same voltage for the Source and Load.

Remove the load and the voltage at the vacant terminals will double.

Correspondingly if those terminals are now shorted, the doubled voltage will appear in the source, leading to high temperatures etc.

Another way of explaining it is to assume that the DC voltage is an extremely low frequency AC; and that the wavelengths involved are extremely large, particularly compared to the usual DC Load demonstration circuits.

Thanks Yarwell.

All done, all finished. And no need for your services even at that discount rate you would have charged me!

My office now has natural light again!

Better buy some new blinds then.