Telephone

[pwdrive]

Had a thread on UKVRR about a phone problem I had, in a nutshell I plugged a new ASDL/Phone splitter (Tristar) to the phone line's master socket, incoming and outgoing calls ok but no ringer.

Tried another phone, no difference, tried an ASDL micro filter (Tristar) still no ringer.

Tried another ASDL filter (Polaroid) and all now ok.

So there it is.

Lawrence.

[ppppenguin]

Presumably a phone that depends on pin 3, the separate ring wire. Many (most?) phones no longer use it. It's possible that some microfilters don't pass it.

AFAIK the ring wire is very much a UK thing. Don't think it's been used elsewhere.

[Terry]

I would imagine that the ring wire or something similar would have been used in any telephone system that used Loop Disconnect (i.e.: Rotary Dial) dialling.

When you turn the dial, the first thing that happens is that a switch closes placing a short across the bell. This stops the dialling pulses making the bell tinkle as you dial.

Without that interconnecting wire, though, all the bells on other extensions on the same line would tinkle. In the days when the GPO, as it was then, owned all the telephone equipment and wiring which was then rented out to the subscriber, a sure sign when visiting someone's house that they had somehow 'acquired' another phone and wired their own extension was the characteristic tinkle from either phone if anybody dialled a number on the other one!

Anyone with a single phone could look inside the junction box and see that only two of the four wires was connected to the line and duplicate that for their illegal extension but, of course, they didn't know what the other wires were for or how to interconnect them between the two phones - which involved removing (different) links in both phones and knowing which wire to connect where!

Another catch for the unwary was that the bells were 500Ω impedance and up to four could be connected in series to give a total load of 2,000Ω

Modern phones have 2,000Ω bells and up to four can be connected in parallel resulting in the same 500Ω  figure we started off with in the first place!

Inside a good old fashioned GPO telephone you would find two rows of terminals comprising, if my memory serves me correctly, 19 in total via which all the various parts of the phone interconnected.

In the simplified drawing on the left you can see the incoming line, bell capacitor, bell and dial shorting switch. When the dial is turned, the bell is shorted out do it can't tinkle. Note all the links!

Connecting two phones together is a bit trickier as you can see on the right. There is only one bell capacitor used and the two bells are connected in series but either dial switch shorts both bells.

To connect a third and fourth phone the same arrangement is used but with extra wires so that all of the bells are connected in series.

DTMF phones don't suffer from Bell tinkle, of course, so the bell wire has obviously been left out of some devices as Lawrence found out with his ADSL filters. As an alternative to finding a correctly wired filter, replacing the extension sockets with Master sockets would also have worked.

   

[Mike Watterson]

UK phones use a capacitor in the wall socket and more than two wires.
Other countries phones don't.
UK market phones and Faxes don't work outside UK unless you use an adaptor with capacitor. Some BT socket to RJ11 plug adaptors don't have this, so phone never rings and fax never answers. Argos now gives free BT socket to RJ11 jack adaptors with the capacitor in it as they insist in selling UK market phones in Ireland, which will never ring if the cable/plug is simply replaced/adapted. The Traditional RJ11 master socket has no ringing capacitor, the UK BT does. It's always best in UK to have an ADSL master socket that has a decent ADSL filter internally and then on phone side the BT type master with the capacitor.

Two additional "gotchas"
1) Israel uses (or did) the BT jack, but instead of two outer pins being Tip & Ring (the live pair), it's the same layout as RJ11, so a crimped straight cable RJ11 (on phone) to two inner wires BT plug <-> Wall Socket. Thus imported UK phones don't work AT all.
2) Some Faxes or POTS sockets on a Cable Modem, while having RJ11 sockets, are wired both the two inner and outer (Presumably so a UK BT plug crimped STRAIGHT to RJ11 works, otherwise you have swap outer & inner wires at one end, awkward). Often connecting a Fax or phone to PABX or POTs that has RJ11, you have to cut the two outer wires of the flat RJ11 <-> RJ11 patch cable. Otherwise it doesn't work at all.

[ppppenguin]

I've fallen victim to the Israel problem. Don't know why they chose the UK connector (and with different pin outs) rather than RJ11 to replace their antique concentric connector.

One day I might disconnect the ring wire at the master socket and see how many of my assorted phones still ring.

[pwdrive]

Maybe it's just me but I can't quite see the need for a separate ringer wire in this modern age?

Lawrence

[Mike Watterson]

I worked in a telecom company before encountering Israel, so I sorted a lot of phones for bemused UK <-> Israel travellers.
I heard a Bezeq explanation of why they didn't use RJ11. I forget what it was. I also heard in 1970s an explanation as to why the UK didn't go for RJ11 (I forget what that was, but it wasn't convincing). There is nothing wrong with RJ11. Originally the inner pair on RJ45 were not used for Ethernet, so people used to use CAT5 and RJ45 sockets for phones and ethernet, as the RJ11 fits in the middle. Then patch in the comms room. Modern 1Gbps ethernet does use all four pairs.

[Crackle]

I may be wrong, things could have changed over the last 10 or so years, but it was my belief that a "legal" telephone installation should only have the one ring capacitor, i.e. one master socket. All extension socket should NOT have a ring capacitor fitted e.g. snipped out, and make use of the 3 wire system.
The purpose of the single ring capacitor I was told is to limit the load on the exchange.

Mike

[AlanBeckett]

The modern requirement is that a Telephone shouldn't 'Harm the Network'. It doesn't actually have to work.
Whether multiple Ring Capacitors meet the above is open to interpretation.

Alan

[Terry]

I don't think it matters, Mike, because of the way the ringer circuit is configured.

In GPO days, when the GPO owned everthing and nobody was supposed to touch the installation in any way, the bells had an impedance of 500Ω. Extension bells were added in series up to a maximum of  4, making a total of 2,000Ω.

Obviously the interwiring to do this was quite complicated. One extension was simple enough - if you knew which links to remove - as the master phone had its ringing capacitor in series with bell as usual, but the link from the bell to the other side of the incoming line was removed. The link in the extension between the capacitor and the bell was removed and a wire joined the floating ends of the bells together, putting them in series.

Adding the third and fourth extensions was a bit more complicated as both sides of the bells needed to be disconnected so that they could be arranged in series and inserted into the bell circuit of the first two phones! 

Then there was the bell tinkle suppression which had to be linked between all of the phones. If this wasn't done, every time somebody made a call, all the other phones would 'tinkle' as the dial pulses were generated.

Obviously, such a complicated system was out of the question when the service was opened up and anybody could add extensions themselves.

The most important change was to change the ringer impedance to 2,000Ω. Extension bells could then be wired in parallel, again up to a maximum of 4, when the figure of 500Ω would be reached.

This is where the REN - Ringer Equivalent Number - came in. The maximum REN is 4 - usually 4 phones - but if anything greedy is connected, that has to be taken into consideration. I would guess that a heavy duty external bell is quite a bit greedier that a normal phone, so assume REN of 2. The maximum number of phones you now have is 2, because 1 + 1 + 2 = 4.

Now for the master socket. Why only one socket equipped with a ringer capacitor? It's our old friend bell tinkle again except that in the new system it doesn't have a separate wire. Quite simply, a short is placed across the ringer whilst dialling. By only have one capacitor and the bells connected in parallel, the bells on all the phones are shorted at the same time. If every socket had its own capacitor and  all the bells are connected in parallel to stop bell tinkle, there would now be 4 ringer capacitors in parallel across the line which might cause some problems to the shape of the dialling pulses, particularly on long lines!

Now, of course, everybody uses DTMF dialling (unless they've got a vintage installation!) so no more bell tinkle. This means the third wire is no longer absolutely necessary if master sockets are installed everywhere. In which case only a 2-wire connection should be used so that, again, the capacitors are not connected in parallel.

Such a system might be frowned upon, officially, but there is no reason that it not work as well as one using the correct wiring layout.