Mobile Exchanges |
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Over the years, a variety of mobile exchanges were built to provide extra exchange capacity where it was most needed and to give emergency cover in the event of a disaster. Typical equipments fitted ranged from special UAX variants, Non-Director to TXE2 as well as containerised Digital and customer switch replacement modules. |
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Pictured is Mobile Non-Director Exchange No. 341 |
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HISTORY of the Mobile |
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The very first Mobile Automatic eXchange (MAX) was brought into service
on 7th December 1938 by the Postmaster General, Major G.C. Tryon, M.P. who
made the inaugural call from Post Office Headquarters to the chairman (Mr.
Hugh de Haviland) of Essex County Council in Chelmsford. After the ceremony,
the exchange was then put to work in North Weald, Essex where it replaced
a small manual exchange. |
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| The MAX | ||||||||||||||||||||||||||
| MAX12s
The early MAXs housed UAX No. 12 type equipment with provision for 100 lines-90 subs. and 10 junctions. The mobile had many special features:- Trailer Design
Once on site, the pneumatic tyred wheels would usually be replaced by heavy cast steel feet, bolted directly onto the wheel axles. Exchange Design
MAX12s were often used to provide service during the conversion from manual working while the permanent auto exchange was being constructed. Typical setting-up time including diversion of local cabling was 2 weeks. MAX13s MAX13s, with a 200 line multiple, were the mobile version of the UAX13 and needed 2 trailers.
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| The Sixties | ||||||||||||||||||||||||||
| Whereas, MAXs were used predominantly for rural areas and to aid the conversion from manual to auto working, the demand for telephone service was increasing and a larger capacity expedient was needed. Two new style mobiles were designed; the MNDX (a subscribers' unit) and the MTX (a tandem unit). In the early Sixties, an initial distribution of 30 units was made to the Regions with more on order. | ||||||||||||||||||||||||||
| The New Mobiles | ||||||||||||||||||||||||||
Mobile Non-Director Exchanges (MNDXs) and Mobile Tandem Exchanges (MTXs). Key features of the new mobiles were:
The first Mobile Non-Director Exchange (MNDX) called Crompton was brought into use in February 1963 as relief to Shaw auto exchange in Lancashire. MNDX1 was produced in 1962 by the Post Office Factory at Enfield. A single MNDX could provide service for 400 subscribers. Later in 1963, relief to Woking manual exchange was provided by Mayford which used two of the MNDX subscriber units and one Mobile Tandem Exchange (MTX) unit to provide 800 additional lines. MTXs utilised some of the equipment within the MNDX, so could not be used in isolation. In the late Sixties, MTXs were produced at the Post Office Factory at Birmingham.
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| The Seventies | ||||||||||||||||||||||||||
In the early Seventies the waiting lists for telephone service were growing
due to the shortage of switching equipment in some areas. To improve
provision, the Post Office placed an order (worth £3 million) with
Plessey Telecommunications for 30-40 new mobile exchanges. The TXE2 electronic
exchange was chosen to bring relief both to small towns and as a temporary
replacement at exchanges undergoing refurbishment. |
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| The MXE2 | ||||||||||||||||||||||||||
The first mobile TXE2 designated MXE2, was operational in 1973 at Padgate, Lancashire to cater for growth in Warrington new town. Many MXE2s were equipped at Plessey's factory in Beeston, Nottingham. Key features were:
The first 2000 line MXE2, of contained within three trailers (2 line switching and 1 control trailer) was commissioned at High Wycombe in March 1974. A reduced battery standby time of 5 hours was possible. Typical set-up time of the MXE2 on-site was approximately 6 weeks.
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| Logos & Serials | ||||||||||||||||||||||||||
POST OFFICE |
GPO |
POST OFFICE |
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| Mobiles were finished in dark green and allocated sequential
unit numbers in white lettering together with 'POST OFFICE TELEPHONES' or
'POST OFFICE ENGINEERING DEPT.' as well as, the superfluous 'TELEPHONE MANAGER'
as many mobiles were used nationally and not assigned to particular
Areas. The GPO logo complete with crown was also used for some time after
the Post Office ceased to be a government department.
MNDX1 carried trailer serial number T11892
Telecoms trailer serial numbers T205000-T207418 were used between
1965 and 1971. Thereafter, the 9 digit telecom vehicle identification
numbers were used. Thus for MNDX No. 331 serial 71 830 0030
the details are as follows:
1971 is the year of delivery (but not necessarily when the racks were fitted). The 830 refers to mobile telephone exchanges and the 0030 is the unit serial number.
Between 1971 and 1981, serials 830 to 834 were also used to designate:
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| The Eighties | ||||||||||||||||||||||||||
| The Eighties saw a steady increase in
the number and capacities of electronic exchanges and the introduction
of digital technology, System X. The Strowger mobiles were becoming outdated
and unnecessary as smaller more efficient switches were being developed.
Strowger was being exported in containers and at home, Commsure was using
the spare mobiles to house replacement PABXs. This was a decade of change
as long established practices gave way to new methods of working. |
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| Containerisation | ||||||||||||||||||||||||||
| In the early Eighties, British Telecom's Teletrade produced
complete Strowger exchanges in insulated, air conditioned standard 20
feet containers for export overseas. The basic unit was 400 lines capacity.
Lettering was British Telecom blue on a yellow container.
Containerised 'reed switching systems' were also produced by Plessey for
both the home and export markets. |
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| Commsure | ||||||||||||||||||||||||||
| Commsure was devised by Phil Taylor in response to customer
demand for an emergency (PABX) switch replacement service that
could be used in the event of a fire or other major disaster
at a business premises. This was necessary as the Stored Program Control
PABXs in use during the Eighties took many months to order and
to program to customer's requirements. The idea was adopted by British Telecom
North East in 1984 and the first units were ready by February 1985.
Commsure units were:-
Additionally, each unit was fitted with a standby power supply and a separate operator suite with space for 2 operators and a manager/supervisor. A full set of alpha directories (on fiche) complete with a microfiche reader was also supplied as part of the package. Once delivered to site and connected to the customer's internal wiring, the units were expected to be loaned for a period of up to 6 months. |
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| The TXD | ||||||||||||||||||||||||||
| The world's first transportable System X telephone exchange
was delivered on 1st April 1987 to BT's East Anglia
District as an expedient to cater for the rapid expansion of the
Port of Felixstowe. Supplied by Plessey Major Systems Ltd of Liverpool,
the RCU (Remote Concentrator Unit) with a capacity of
approx. 1500 lines, was housed in a standard 30 ft container which
was positioned by a heavy lift 'Quinto' crane. The exchange keys were handed
to EAD's District Manager, Colin Coleman by Plessey's Paul Leidecker. |
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| The Nineties | ||||||||||||||||||||||||||
| The Nineties saw the end of the Analogue
exchanges with the majority of the Strowger and Electronic mobiles
having been stripped-out for use as storage units, mobile shops and
other purposes. Fully-equipped surviving units are rare, but examples
can be seen at museums and preserved railways. |
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| Network Mobiles | ||||||||||||||||||||||||||
| The digital network is perhaps more prone to a major failure
as a result of human error such as a software problem (e.g.
the 'Year 2000 bug') than the more resilient Strowger days. Even so,
modern equipment is still vulnerable to fire or flood and there is still
a need for mobile exchanges as we continue to rely upon the telephone service
as a vital communication aid in today's global village.
To this end, the concept of mobiles still have a place as
containerised digital node switches which have been produced to replace
at short notice any trunk switch in the event of a serious failure. |
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| Two Thousand & Beyond | ||||||||||||||||||||||||||
| Having reached the new Millennium, mobile
trailers could be used for conceivably any purpose ranging from a complete
Personal Computer (PC) equipped office, Internet node, mainframe system,
microwave link-up and broadcasting, as the various communications medias
merge into a single data-stream.
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| Links to other mobiles | ||||||||||||||||||||||||||
MNDX No. 318 & 71 830 0023, 71 830 0098, 72 830 0051, 72 830
0074 have been seen at Ardrossan, Ayrshire. One was seen painted
in 'Business Systems' dark blue.
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| Acknowledgements | ||||||||||||||||||||||||||
| Telephony by Atkinson; Chris Barlow; Mike Fletcher;
Martin Loach; Peter Walker; Post Office Telecommunications Journals;
Telephone Museum, Milton Keynes, & Phil Goodwin; Kent & East Sussex
Railway, & Nick Wellington; Post Office Vehicle Club; THG; Teletalk,
staff newspaper of EAD. References:
POEEJ Vol 31 October 1938 -Inauguration of the First Mobile Unit Automatic
Exchange.
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