From: marcusj@apricot.co.uk (Marcus Jenkins)
Newsgroups: comp.dcom.modems,sci.electronics,uk.misc
Subject: UK phone circuits vs. US phone circuits
Date: 11 Jan 93 08:59:51 GMT
Organization: Apricot Computers Limited


I need some clarification of UK telephone circuits
and how they map onto US ones.  I have just bought
a UK-US telephone adaptor, but when I opened it up
to have a look at what was connected to what I got
rather confused.  Here's how it's connected:

First let's get a common reference for the 
connectors:


    ---------		
    |       |       An illustration of a US 'phone
  ---       ---     connector in my best freehand 
  |           |     ASCII.  (Looking at the open
---           ---   end of a socket).
|               |
|               |
|               |
|               |
|  | | | | | |  |
-----------------
   6 5 4 3 2 1 



   6 5 4 3 2 1
----------------|||   An illustration of a British 'phone
|  | | | | | |  |||   connector.  (Looking at the top of
|  | | | | | |  |||   a plug.
|  | | | | | |  |\\ 
|  | | | | | |  | ||
|  | | | | | |  | ||
| ------------- | \\
| ------------- |  ||
|  | | | | | |  |  ||
|               |  ||
|               |  \\
|               |   \\
|  -----------  |    \\
|  | |     | |  |     \\
|  | |     | |  |      \\ 
|  -----------  |       \\
|               |
-----------------

What my adaptor does is:



UK plug                    US socket

BT ID  pin                 pin  label in socket

A wire  5   -------------   4   T1 (tip cct. 1?)
B wire  2   -------------   3   R1 (ring cct. 1?)


Do all US circuits really only have the 'tip' 
and 'ring' connections?  (I have looked at the
2nd Edition of 'The Art of Electronics' by 
Horowitz and Hill and can't see anything to 
the contrary.)  Why do we (in the UK) need 2 
or more wires to do the same job?  This especially
of concern when I was under the impression that
you *can* (as opposed to *may*) connect your
average modem, for example, that you buy in the
US to the British 'phone system and it will work.

In the BT circuit there is a local earth and a
shunt wire connection (on 4 and 3 respectively of
the BT plug).  In the US 'phone socket box for the
adaptor described above, there are also the GND
and AUX connections (on 5 and 2 respectively).
Why aren't the grounds connected through in the
adaptor?  What is the 'shunt wire' connection in 
the Uk circuit (and how is that different from the
AUX connection in the US circuit?)

As you may have guessed all of this is to find
out how to connect a US modem to the UK 'phone
system.  As far as I know people have done this
and it works.  I assume that the adaptor I have
described above will do the job.  However, the 
fact that it appears to be rather minimal is a
bit worrying.

I am quite aware of the British BABT 'phone 
apparatus approval system which makes it
illegal for me to connect non-BABT approved
equipment to the British 'phone system directly.
Therefore consider my enquiry as purely a 
hypothetical excercise.  I would never dream of
breaking the law (however petty it might be and
even if it was produced principally in the 
interests of preserving vested interests of a
fat monopoly like BT (and of course to prevent
bozos from connecting the mains at 240V into 
the 'phone system which is what I expect anybody
from BT will tell you was the sole reason)
- flame off).
 
Thanks in advance.

Please mail me.


 _ _ _
' ) ) )                         Internet: marcusj@apricot.co.uk
 / / / __.  __  _. . . _        UUCP: marcusj@apricot.uucp
/ ' (_(_/|_/ (_(__(_/_/_)_      If all else fails from US, try:  
Marcus Jenkins                  apricot!marcusj@relay.EU.net
Tel: +44 21 472 3002  Fax: +44 21 471 2935
Disclaimer:  Anything I wrote above is, of course, my own view and
             does not in any way represent my employer.