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Author Topic: Voltages on the metallic path facility  (Read 627 times)

Weaver

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Voltages on the metallic path facility
« on: November 29, 2020, 03:37:41 AM »

This seems like a stupid question but I realise that I have never known the answer. In DSL, if you measure the potential differences between the A conductor and true earth (the planet) and the B conductor and earth, what will those potential differences (voltages) be? Iím wondering if A = X Volts and B = -X Volts ? Or whether one side is 0 V or what ?
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JGO

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Re: Voltages on the metallic path facility
« Reply #1 on: November 29, 2020, 08:22:49 AM »

With PERFECT balance,  one side is  at V volts wrt earth and the other is -V.  In practice they wont be exact, With care the out of balance component (ie same on both sides) is typically - 30 dB probably better is possible at audio frequencies.
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roseway

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Re: Voltages on the metallic path facility
« Reply #2 on: November 29, 2020, 10:07:44 AM »

Assuming that you're talking about the on-hook DC voltages, then the A leg is at ~0V relative to earth, and the B leg is at -50V.
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  Eric

Weaver

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Re: Voltages on the metallic path facility
« Reply #3 on: November 29, 2020, 03:22:07 PM »

And the signal voltages, on top of dc? Are at +V and -V ?
« Last Edit: November 29, 2020, 10:16:20 PM by Weaver »
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tubaman

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Re: Voltages on the metallic path facility
« Reply #4 on: November 29, 2020, 03:42:55 PM »

Out of interest I've just measured mine with respect to mains earth (which is connected to a long copper rod in the ground at the side of my house).
I got A = +3.5V, B = -53.3V.
 :)
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burakkucat

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Re: Voltages on the metallic path facility
« Reply #5 on: November 29, 2020, 04:23:13 PM »

Sand the signal voltages, on top of dc? Are at +V and -V ?

With xTU transceivers connected (and operational) at either end of the link the RF voltage present is miniscule. It is impossible to measure with the average DVM. Perhaps with a high quality, high bandwidth, oscilloscope something might be seen . . .
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Weaver

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Re: Voltages on the metallic path facility
« Reply #6 on: November 29, 2020, 10:47:04 PM »

@tubaman: thank you very much!

@burakkucat: Agreed. :-) Iím not sure what the signal voltage at the ATU-C end is in my case but downgrading that by 64 dB is going to have an impressive effect, 1V reduced down to 0.631 mV, according to my calculator.

I was wondering if the signal voltages were antisymmetrical.
« Last Edit: November 29, 2020, 10:49:17 PM by Weaver »
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