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Post Office Radiophone Service
         
 
Page Updated 28 Sept. 2005

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UK Mobile phone history

With the UK introduction of 3G third generation cellular mobile phone services, you could be forgiven for thinking that the '1G' analogue cell phone marked the beginning of the story but in fact cellular technology was pre-dated by another four generations...
 
         
 
Radiophone Exchange
 
System 1
 

The very first public mobile telephone service in the UK was made available in 1959. It was of limited capacity and provided coverage in the South Lancashire area.

It was not until 1965 that service was made available in London. The launch coincided with the opening of the Post Office Tower, which was the location for the base station transmitters covering the central London area. The launch of system 2 saw the beginning of the ever increasing rise in popularity of the mobile phone.


 
         
 
Storno 9 Channel Radiophone
 
System 2

9 Channel Radiophone

By the early 1970's the state of the art was the Nine Channel Radiophone. There were only three authorised suppliers of equipment, Storno, Pye and Marconi.

The installation typically consisted of a control head, handset and loudspeaker fitted in the front of the vehicle, connected to a transceiver unit usually mounted in the boot connected to a whip antenna. Storno also produced a transportable battery operated version for pedestrian use.


 
 


Coverage and capacity

 

The coverage maps show service was gradually extended to cover London, Birmingham, Bristol, Manchester, Newcastle and parts of Scotland. Although refered to as the nine channel radiophone, in fact the equipment had ten channels, nine manually selectable for initiating calls, and 1 for incoming call signalling (automatically selected when the handset was resting in it's cradle). Each subscriber was allocated a five digit number. London numbers always started with a 1, Provincial numbers varied by area. This also affected which group of nine channels were supplied (i.e. not all users had the same nine channels, six different channel groups were available).

 

Operation

 

A mobile call was initiated by lifting the handset, manually selecting a free channel and pressing the call button (specific channels were used in specific areas, busy channels were indicated by an engaged light). A ringing tone would be heard until an operator answered. The subscriber would give their five digit mobile number followed by the number they wished to call. The operator would make the connection and the call would continue until the mobile replaced the handset in the cradle which would clear down the call. It should be noted that from the mobile perspective the conversation was one way at a time, the transmit button on the handset had to be pressed to talk, released to listen.

 

To call a mobile from a fixed telephone it was necessary to call the radiophone operator by dialling 140 (in London) and requesting the 5 digit number of the mobile you wished to be connected to. The operator would key in the number which would be transmitted using a 5 tone sequence to all mobiles on the calling channel. The mobile, if available would respond with a single tone to acknowledge the call. The mobile would be alerted and could respond to the call using the same procedure as for a mobile initiated call, with the small difference that the tone sent when the mobile initiated the call would be different, this would give an indication at the exchange as to whether it was a mobile initiated call or a response to an incoming call.

 

Security

 

You may wonder what was to stop somebody 'pirating' another number when initiating a call. The answer is not much but remember these were simpler times! As for the possibility of monitoring other people's conversations, the control logic tried to prevent this but some users discovered you could lift the handset, select an engaged channel, then remove the antenna, press the call button then replace the antenna. You could then hear the conversation on that channel.

 

Alternatives

 

The General Post Office - GPO had an almost total monopoly on telecommunications in the UK at this time and the regulations concerning interconnection between other radio systems and the public telephone network restricted operation to emergency use only. The only 'competing' service was exclusively for marine use. The other alternative was to use message handling services provided by companies such as AirCall, ReadyCall, Selective Audio Messaging and Securicor.

 
 
Storno 55 Channel Radiophone
 

System 3

 

55 Channel Automatic System

 

The system was further developed with the arrival in 1977 of the Storno Fifty-Five Channel Automatic Radiophone. This had the advantages that an idle channel was found and called automatically, just by lifting the handset. Also because the unit could automatically scan all the available channels there was a much better chance of finding a free channel quickly.

 
 

System three was an 'overlay' system which used the same frequencies and calling channel as the 9 Channel system. Idle channels were identified by a marker signal consisting of a two-tone combination. Different combinations were used in different parts of the country. The mobile had a six button area selector marked A E I O U and X, although only the first three were physically enabled. London area used button A which had a marker tone combination of 2000 Hz and 2200 Hz. When the subscriber lifted the handset from it's rest the mobile would scan all the channels searching for the marker signal and  the control logic could also sample the strength of the received signal to ensure a good quality connection. Once a good signal had been detected the mobile sent the call tone automatically and the ringing tone would be heard until the operator answered. Apart from the automatic search, the operation was similar to the 9 channel equipment

 
 
Stornomatic 900 PRT4 Radiophone
 

System 4

 

Automatic Direct Dial System

 

All the previous systems relied on an operator assisted connection to the subscriber but 1983 brought the UK's first direct dial carphone. The National Automatic Radiophone Service (also known as Public Radio Telephone System Four or PRT4) used full duplex two-way transmission, removing the need for a press to speak button. It also provided a service with greater geographical coverage.

 
 


This final incarnation before the advent of cellular systems also used the same frequency range as the earlier 55 Channel system and in order to provide more capacity it was necessary to modify all the existing 9 and 55 channel equipment from 25 kHz to 12.5 kHz channel spacing. This allowed the new system to interleave with the existing system without causing interference and then to gradually increase capacity while phasing out the old manual system. The system had 95 channels and the system coverage area increased to provide service in most of the major population centres.

 

The Stornomatic 900 installation was similar to the previous models with a control box usually fitted under the dashboard and the transceiver unit in the boot. The control box had a numeric keypad and display and facilities included some now familiar user features such as number memory and security lock codes.

 

To dial a mobile number it was necessary to dial a regional area code related to the location of the mobile, followed by the six digit mobile number. To call mobile 215063 in the London area one would dial 0034 215063.

 


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