Historical telephone sets
This section of the website is about historical telephones
that are mentioned or featured elsewhere on this website. These pages are
by no means intended to give a complete overview of historical telephone
sets, but act merely as a placeholder for background information on them.
For telephones with cryptographic features, please check our
page about crypto-telephones.
Telephone sets featured on this website
Old analogue telephone lines (POTS) commonly only need two wires for the
connection between a telehone set and the telephone line. Power, signalling
and audio is passed over these two wires. Although there are many different
designators for these wires, the most common European name for them is
(A) and (B). In the US, they were known as Ring (R) or (-)
and Tip (T) or (+). Furthermore, each country used to assign its own
colour scheme to the wiring.
To avoid confusion, we will use the European designators
(A) and (B) here,
and colour them red
and blue respectively.
Modular jacks — also known as Registered Jack (RJ) connectors —
are a relative simple yet
reliable way to connect (analogue) telephone equipment to a telephone line.
The connector was initially developed in the United States, but has since
been adopted worldwide. They exist in many forms:
Although there are many variations, the most popular ones are shown above.
The specified pin-numbering is when looking into the female socket,
(i.e. not the plug).
At the centre are the sockets that are used for connection to old analogue
telephone lines (POTS), with the official modular designator at the
bottom. It shows the number of positions (P) and the number of actual
contacts (C). To avoid confusion, the official designator should be used
instead of RJ-something.
At the right is the RJ45 or 8P8C ethernet connector, which is shown here
for comparison only.
In the US, 6P2C, 6P4C and 6P6C connectors were used for single-line,
two-line and three-line configurations respectively, as shown in the
diagram below. The most common wiring is for a single-line, which is
always connected to the middle two contacts, regardless the connector
type. The single-line US standard was adopted by most countries
in the world, with some exceptions.
In Europe, the situation was much more complicated, as each country
traditionally had its own type of connector and wall socket. The
introduction of the Registered Jack did not take place until the mid-1970s,
when foreign equipment was gradually being allowed on European networks.
Although most countries have meanwhile adopted the American standard –
shown on the left – the UK uses the outermost two contacts of a 6P4C
connector, whilst Belgium uses the rightmost two contacts. This leads
to compatibility issues when connecting foreign equipment to a line.
To avoid confusion, Crypto Museum suggests to wire the wall socket as
per rightmost diagram.
With analogue lines (POTS) gradually disappearing and ethernet cabling
becoming much more common, we have been looking for a simple way to distribute
old analogue lines throughout the premises, using modern cabling
standards, such as Cat-3,
and RJ45 jacks.
Above is the wiring scheme we use at Crypto Museum for the connection of up
to four analogue telephone lines via regular ethernet wiring, taking the
common twisted-pair wiring layout into account. We have created small breakout
boxes to provide upto 4 analogue lines, some of which we have modified
by shorting lines 3-5 and 4-6, so that one of the sockets will accept any type
of 2-wire equipment, regardless the connection variant (American, European,
British or Belgian).
Below is the wiring for a standard handset as it is used on most modern
POTS telephone sets. It uses the smaller RJ9 (4P4C) connector that is in
most cases wired with a coiled cable.
RJ45 Ethernet wiring scheme
Below is the colouring scheme that is commonly used for RJ45 (8P8C) connectors
in combination with Cat-3 or Cat-5 wiring, when looking into the socket.
Any links shown in red are currently unavailable.
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© Crypto Museum. Created: Thursday 30 March 2017. Last changed: Friday, 18 June 2021 - 06:18 CET.