This not important ....

[clint_flick]

Hi

Vodafone VOIP adapter, by whatever name ..........

Ignore the orientation.

But it seems that a capacitor is fitted which may make it polarity conscious.

A pair of wires to 2 and 5,  RD & GN although I cannot assign pin numbers to colour.

Otherwise I believe it is a simple pin 4 & 5 OUT US style;   to  2 & 5 UK style IN.

[Jayach]

That's not quite how I read it, the reversal is a reversal, but the circuit won't trigger unless the reversal reaches 15 volts. 

The picture that hasn't been moderated yet is an automatic Bing reply when I searched "British Telecommunications (BT) Standard CDS™ for Calling Line Service" (which is creepy as I was searching Google, but using Edge)

I can see I'm going to have to carry out a test, just to fully satisfy myself.

If I don't take my service down, I'll report back.

[Ripshod]

You'll need an oscilloscope with the trigger set for 20 volts or so.

It's not a polarity reversal. As you'll see it's just a signal reversal. In the case you stated with a dc voltage of 48V, the audio signal is injected on to that voltage. So while the mean voltage remains at 48 the audio swings that by roughly 24V, so the peaks would be at 60V and 36V.

At the receiver (the phone) the dc is filtered to use for power (not usually needed these days) and the audio is filtered off for obvious uses. The signal "reversal" triggers the phone to listen for the data package. 

[Ripshod]

BTW, it's been a long time since BT and openreach split into divisions. That info must be very old. 

[Jayach]

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@Ripshod wrote:

BTW, it's been a long time since BT and openreach split into divisions. That info must be very old. 

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The way the equipment works hasn't changed, just because the name has changed.

[Jayach]

O.K. I'm back, and I was kind of right.

My line sits at -50 V, and reverses to +50V whilst ringing. During the call there is no discernible voltage.

On ending the call it returns to -50V (I thought it would stay a +50 until the next call comes in, so there I was wrong)

At least now I know, just in time for it all to become history. 🤣

[Jayach]

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@Jayach wrote:

My line sits at -50 V, and reverses to +50V whilst ringing. During the call there is no discernible voltage.

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Of course, I may have had the probes the wrong way around.

It would be interesting to carry out the same test on a line that doesn't have CLI.

[Ripshod]

Did you test with a DMM? Unfortunately you never saw the signalling.

I was also given bad information then. I haven't got the time right now to compile a list of documents, but the same as you I think it's a little late to be learning about soon-to-be history. It would be good to revisit in 20 years or so, to mull over the simplicity through moist eyes. 

I just do the connections, the exchanges are openreach's problem. 

[Ripshod]

Standard pair connection in the BT socket are white/orange, the white being the +ve. 

[Jayach]

Yes a DVM, I don't have an oscilloscope,

The cable I connected into the BT socket (see still called BT even though they are now Openreach) was a cable cut off a DSL filter. The wires were green and red. The correct polarity wasn't important as I was only looking to see if it reversed.

[clint_flick]

Hi

Something I made a coupla years or so ago, during lockdown probably .....

Not polarity conscious coming in, and the capacitor is upto 250 volts.

So maybe the router is ""identical"" and the capacitor goes across to pin 3 ???