What should the Copper Phone Line Voltage be ?

[mrflack]

I am trying to test my broadband and want to know what voltage I should ne getting from the outside line, can someone help ?

My broadband is working but drops out, I measure a fluctuating -40mv from the outside wiring.

[Cynric]

@mrflack  The Google search result is here https://en.wikipedia.org/wiki/British_telephone_socket 

[Jayach]

From memory, it should be approx 50V. If you have CLI on, when a call comes in the polarity will reverse.

[mrflack]

Thanks Jayach, would you remember if this 50v is measured across A&B using a standard voltmeter?

[Jayach]

Yes, directly across the incoming pair of wires.

There is a post somewhere on here where I carried out that exact test, to see what happened with CLI, but I can't find it now.

[Jayach]

You may find this helpful https://telephonesuk.org.uk/how-a-phone-line-works/

[Jayach]

Found the original thread, and my post where I carried out the test.

https://forum.vodafone.co.uk/t5/Landline/This-not-important/m-p/2736475/highlight/true#M2898

[mrflack]

Ok from reading your replies I have learn't a hell of a lot and I thank you for your time to explain the telephone system operation to me. What I cannot understand is that from the pole where the phone cable attaches to my house I read +/-40Mv not +/-50V on the twisted pair copper wires.

I have no landline and the voice system has now been disabled by Vodaphone, would that effect the voltage?

I will do a video at the weekend to show what I'm getting, I hope one of you experts can see what I'm doing wrong or if indeed I have an issue.

Thanks again 🙂 

[Jayach]

Personally, if your broadband is working apart from the occasional drops, I doubt the presence or not of the voltage is relevant.

When it's working, do you get the expected sync speeds?

Just how do the drops present themselves, how long do they last and how frequent are they?

Perhaps if you post your DSL stats that may show something.

DSL Status Information

DSL Mode

ITU-T G.993.2_Annex_B (VDSL2)

DSL Uptime

7 days, 6 hours, 50 minutes and 3 seconds

Line Coding

DMT

Status

Connected

Number of Cuts

0

Link Power State

L0

Line Quality

  Downstream Upstream

Current Rate	79188 kbps	20000 kbps
Maximum Rate	81004 kbps	24479 kbps
Signal-to-Noise Ratio	4.3 dB	8.4 dB
Attenuation	DS1 9.0 dB, DS2 21.7 dB, DS3 33.7 dB	US0 2.0 dB, US1 14.9 dB, US2 24.2 dB

[mrflack]

Hi again, my speed seems fine 52-55mbps, the drops are intermittant (hence vodaphone ststing every time the line is fine) it's random and takes a few seconds or so before the signal is re-established. I have a backup from vodaphone with a sim inside and this is suppossed to take over in case of signal loss but this is not instant so when watching a film for instance the film freezes and takes a a good few seconds before it starts again. Sometimes I even have to re-connect the wifi to the router.

Forgive my lack of knowledge but how do I monitor and check my DSL stats?