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9. TECHNICAL
This section contains information or publications that is of a technical nature and was produced by the Directorate.
Some of the articles may relate to notes of a meeting, or presentation. Others may relate to documents that were circulated internally, possibly distributed externally, as part of a project, feasibility study or R&D exercise.
Documents currently in this section are as follows:
Automatic Vehicle Location Systems (AVLS) Forward Planning Presentation
This document is a set of notes produced for a Forward Planning Presentation held on the 17th June 1975. The notes highlight a number of methodologies open to the Directorate at that time associated with Automatic Vehicle Location Systems (AVLS) and possible deployment with UK Police and Fire Services.
All the systems on offer at that time were ground based networks, as the Global Positioning System (GPS), utilising a network of strategically placed satellites, was not an option in those days as it was some 15 years later before it came into service!
Credits
This document was kindly provided by Mike Brain and is Crown Copyright.
QSAM Radio Schemes; their preparation and adjustment
 This small document published in January 1985 describes the preparation and adjustment of Quasi-Synchronous Amplitude Modulated (QSAM) Multi-Station Radio Schemes used by Directorate customers for country wide radio coverage.
During the late 1960's and early 1970's, Police and Fire VHF county-wide radio communication used spaced carrier for simultaneous transmission from hilltop sites to mobiles, ie: -3KHz and +3 KHz of the allocated RF Channel for a two site scheme, or other combinations for a given number of sites within the 25KHz channel spacing available at that time. This was done to ensure that the resultant audio mix would be outside of the 300-3,400 Hz audio band and therefore not audible to the end user.
As spectrum demands grew in response to user requests for more traffic channels during the 1970's, there was increasing need to ensure effective and efficient use of the limited spectrum available to Police Forces and Fire Brigades.
The availability of cheaper high stability oscillators during the 1970's enabled main transmitters to be held within a few Hz of their nominal RF channel for long periods of time. Together with a large procurement programme by the Directorate for Pye Radio Link Assembly (RLA), high quality delay circuitry needed to correct bulk delay site distance differences and audio phase compensation correction to ensure that all sites transmitted in-phase for good speech clarity, most county-wide users were eventually changed over to QSAM, which freed up more channels for subsequent re-allocation. In addition, at some point during the 1970's and early 1980's, many of the links were modified from 25KHz to 12.5KHz to free-up spectrum in the 146/152 link band.
By the time the WARC changeover program took place during the 1980's, the Directorate had amazed a wealth of expertise associated with QSAM. However, setting up procedures needed to be revised as Police users were being migrated from the 25KHz spaced 80/100 MHz band to the 12.5KHz spaced 143/155 Mhz band and Fire Brigades were migrated to 12.5 MHz spaced 70/80 MHz band. Tolerances were now much tighter and phasing was more important to ensure that good communication existed at all times between control and mobiles.
This document outlined the preparation and adjustment of QSAM schemes and gives an insight to the methodology proposed by the Central Communications Establishment (CCE) based at Harrow in 1985.
Credits
This document was kindly provided by Mike Brain and is Crown Copyright.
Technical Memorandum
 This section contains just a small selection of the many technical memorandums that were produced by the Directorate. The documents were bound in distinctive pink front and rear covers.
As far as I am aware, they were first produced by the then Research & Development Section during the 1970's and in later times emanated from the various engineering groups, mainly based at Horseferry House, from around 1980s. I would guess a number were also written by groups based at CCE Harrow.
Three documents in this section are:
- Technical Memorandum TM36 - Quasi Synchronous Operation in UHF FM Personal Mobile Radio System
This document was produced in November 1979 by Tony Kent. The memorandum reports on the results of laboratory simulation and a field trial associated with Quasi-Synchronous working for increasing the coverage of UHF FM Personal Radio Schemes.
Credits
This document was kindly provided by Mike Brain and is Crown Copyright.
- Technical Memorandum TM47 - Assessment of Filter Characteristics for Subliminal Digital Data Transmission in Speech Communication Channels
This document was produced in January 1980 by John Hollis. The memorandum outlines the results of a brief project to look at the most suitable section of the speech band to use for data signals and to get some appreciation of the characteristics of the required stop band filter.
Credits
This document was kindly provided by Mike Brain and is Crown Copyright.
- Technical Memorandum TM65 - The use of Interference Cancelling Aerials
This document was produced in May 1983 by Derek Smith. The memorandum reports on experiments carried out by the Directorate to ascertain the feasibility of using interference cancelling aerials to minimise the effect of "Rusty Bolt" intermodulation interference to base station receivers.
Credits
This document was kindly provided by Mike Brain and is Crown Copyright.
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10. POST WARC FREQUENCY CONVERSION
 In October 1983 the Directorate published the equipment handbook for the emergency services entitled 'Post-WARC Frequency Conversion Programme'. The handbook presented forces and brigades with advance information on the new replacement equipment's that would be operating in the new VHF frequency bands from late 1985 onwards.
These equipment's would be replacing the ageing 80-100 MHz equipment that had been in operation since the late 1950's onwards, and were occupying part of a frequency band that was to be vacated as a result of the 1979 World Administrative Radio Conference decision to use that band for VHF commercial and public broadcasting radio services.
The handbook contains a brief overview of each of the major equipment's to be offered to forces and brigades, together with indicative quarterly rental charges. Users, would then refer to this manual ahead of more detailed information when planning future purchasing requirements at that time.
Credits
This document was kindly provided by Mike Brain and is Crown Copyright.
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In 1984 the Directorate published an A5 sized booklet which gave a brief overview of the work undertaken by the organisation and the group structure at that time.