Hand Over Slave Equipment

H.O.S.E. 

(System 4 Hand Over Slave Equipment.) 

Sadly this system was in the final process of development about 2 years before the takeover of the embryo TACS Cellphone system that became so well established in the UK. 

There had been previous attempts at continuous System 4 mobile communication using base stations that were connected to a common hub, spaced such that their channel coverage overlapped  at the fringes of their 25 mile radius range, (cell). 

This was fraught with difficulties because although all of the transmitters and receivers in  any particular channel chain were crystal controlled, there were phase conflictions in the fringe  areas where the received signals overlapped and were cancelled by the adjacent transmitters causing loss of connection. 

A scheme to eliminate this problem was envisaged by Mr. Tony Whittaker where, for  example there were 4 base stations in a chain, only stations 1 and 3 or 2 and 4 which were out of  each others range were active for 3 seconds at any one time thus isolating them from adjacent  stations. A cycle of 3 seconds on and off was sufficient time for a mobile to listen for a free channel, latch on and connect. 

The H.O.S.E. control hub equipment was designed and constructed at the System 4  laboratory in Ebery Bridge Road, London. An on/off audio control signal was sent to each paired base station which was filtered out at the base station before any audio was transmitted. Similarly  

an audio tone was returned from each receiver's squelch circuitry to the control hub to determine the received signal strength. The hub would then select which receiver in the chain had the best  reception and would then switch the associated transmitter on, all the other transmitters in the chain  would remain off unless individually selected. 

Initially computer control of the equipment was undertaken by an Acorn BBC home computer and the control software was written in BBC Basic. Later bespoke control boards were  used, and the control programme was compiled in machine code using a commercially produced  software compiler. The processor used on the boards was a Zilog Z80 CPU running at a clock speed of 4Mhz. 

The M23 was chosen as a test route with base stations set up at Reigate, Crawley telephone  exchange, Handcross and Brighton racecourse, Reigate was paired with Handcross and Crawley  was paired with Brighton. Each base station was equipped with 4 channels and Crawley Telephone  Exchange was where the original call handling equipment was housed. The handover equipment  was set up in the paging transmitter room of the telephone exchange with 3 sets of 4 landlines  radiating out to Reigate, Handcross and Brighton, Crawley base station was connected directly. 

System 4 Radiophone was a very basic analogue system, but in it's day fulfilled a useful  service. It was not in the least secure and anyone with a radio scanner could eavesdrop on any  ongoing conversation, what is more it did not have the capability of calling the emergency 999  services directly, this had to be done via the operator and in the hands of an inexperienced telephone operator, was sometimes dismissed as a hoax unless the attention of a supervisor was requested. 

As far as I can remember the H.O.S.E. system operated successfully for about a year and it  was planned to open a similar network along the A9 in Scotland until System 4 was closed and  disbanded in favour of the new more sophisticated TACS Cellphone system. 

R.C.Miller, 15/07/2026.