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DAVE MCKAY G1JWG
Wireless use 1920-1945
UK POLICE RADIO USE 1920 TO LATE 1940s
During the1920s while the Metropolitan police were carrying out their experiments at the Epsom Derby, a visitor to witness events was the chief constable of Lancashire and in the mid 1920s he introduced similar wireless experiments in the Lancashire area, he was not the only Chief constable interested in wireless experiments. The chief constable of the Argylle police applied for permission in 1922 to install wireless transmitting and receiving apparatus at Lochgilphead. The purpose of which was to provide communication to outlying areas of his area. This permission was granted. Because of the size of the area he wanted to cover, a power of 500w was authorised. This was to be on the wavelength of 320m. I have been unable to find any information that would indicate that this experimental use of radio took place but I can find no reference to the issuing of a call sign for this station so it may never have got beyond the initial planning stages.
The Cornwall force were issued with the call sign 6PS in May 1924 and authorised to conducted experiments between 150Mtrs and 200Mtrs from a fixed station at Newquay and a mobile but at a distance not more than 10 miles from Newquay with a power of 10watts using CW or voice. A system was also authorised in Lancashire to operate at about 190m and 440m and had the following call sign issued to it, 2JO and 2PB with 2PB1-4 being fixed transportable. In 1925 a number of other permits were issued, Harrow fire brigade 320mtrs 10W, Blackpool fire brigade 320mtrs 10w. A number of permits were also offered but do not appear to have been taken up. They were to Salford fire brigade 320mtrs 100w, Ashton under Lyme fire brigade, 320mtrs 10w and Burnley fire brigade 320mtrs 10w.
In 1927 the West riding of Yorkshire police were authorised to establish stations on a wavelength between 150 and 200mtrs at Wakefield 5YW with 60w, Selby 5ZS with 10W, Settle 5ZL at 10W and a mobile station 5ZP with 60W.
Following these initial experiments on a number of different frequencies it was decided that there needed to be frequencies allocated on a formal basis and in 1929 a number of channels just below 150mtrs were allocated for police and fire brigade use.
FREQUENCY PLAN 1929
The Metropolitan police were also experimenting with portable radios. In 1930 H.W.Adey had designed a radio set weighing under 5lbs and it had been trialled by the Metropolitan police but while the range was stated as 10-20 miles reception was intermittent and interference high so was not taken up. The newspaper article cites it as a two valve transmitter and receiver. However I believe this to be mistaken and would suggest it is just a receiver given the state of the technology at the time. However if it is not just a receiver the stated range with such an inefficient antenna and limited power from a small battery would be incredible.
Original photograph of officer and H. W. Adey
With the introduction of these allocated frequencies for police use and the change from experimental to operational use, this also prompted a change from the Number-letter-letter format of call sign which were experimental call signs, to three letter call signs beginning G. By the early 1930s a number of police forces had introduced wireless systems and in October 1932 a demonstration was given to Newspaper men and Magistrates of radio transmissions to Police motorcycles in Glasgow in a simulated smash and grab raid. An experimental wireless transmitting station call sign G6KF was installed at Police HQ operating on a wavelength of 150mtrs When the transmitter was activated a red light on the receiving equipment illuminates and the officer operates a switch to listen to the message. The Standard Company designed the equipment.
Liverpool City Police calls sign GTM had introduce initially a telegraphy station and then in 1936 a telephony system. this was one of the first provincial two way systems.
A number of Police forces adopted one way systems namely the Brighton police, the Newcastle Police and also the Stockport Police. While the Metropolitan Police continued with the use of telegraphy (Morse Code) these other forces were using telephony.
Metropolitan Police radio operator
Brighton police radio system. Call sign GTN
The Brighton Police system uses Telephony and a bell call system. It came into operation in September 14th 1933 and was due to the foresight of the then Chief Constable Charles Griffin. Having received Rome on a table wireless he thought that it must be possible for police messages to be sent over the few miles covered by the Brighton Borough Police area to small transportable wireless sets. He commissioned one of his officers, a radio enthusiast to build a set, but this was too bulky for practical purposes but the experiments were published and came to the attention of an amateur wireless engineer Colin Begbie, who at the time was unemployed. He came up with a design for a single valve regenerative receiver, which was small enough to fit in a police officer's tunic breast pocket. This had a separate earpiece but not the small earpiece we associate with modern police radios but more the size of a telephone handset. 30 sets were purchase at a cost of �443.10s equivalent to about �21000 in 2014 and Begbie was appointed to the CID staff. This system operated on 147.8 metres 2030Kcs. The transmitter, which was built by Plessey and had a power output of 100w, was located in the Town hall with the aerial on the roof. The transmitter is described in Post office technical report TCB226/247 September 1933, as using a free running oscillator using a Mullard T61D valve in a reverse feedback circuit, which is shunt fed. Modulation is by choke control with a Reiss microphone being amplified by a 3 stage, LF amplifier feeding a Mullard DO200 valve.
When the transmitter was operated this caused a drop in the current in the anode circuit of the receiver. This caused a relay to operate and a bell to ring. The officer would take out the earpiece and hold it to his ear and at the same time pressing a button. This deactivated the relay stopped the bell and fed audio to the earpiece. The message would then be passed by voice in a code or an instruction given to attend a police box for the officer to be given further information. The code used was very rudimentary with essentially word substitution for offences and instructions. Brick-Burglary, Frog-Fraud, Hoax-Housebreaking,
Brighton pocket receiver 1933
This was only one-way communications but most certainly the first pocket radio used by the Police. These sets gave good service remaining in use until the early 1940's.
The Newcastle Police radio system. Call sign GTT
This was another oneway system operating on 150mtrs. It is described on Post office technical report TCB226/253 November 1933. Standard Telephones and Cables Ltd of Hendon London constructed the equipment. The transmitter is crystal controlled with a master oscillator 4205D valve with an output of 5 watts. The crystal is temperature controlled and a spare crystal is on standby ready to be switched into circuit should the one in use fail. This oscillator feeds an amplifying stage consisting of two 4012A valves with their grids in Push Pull and their plates in parallel. The output from this stage is coupled to a stage using 2 4212D valves operating in push pull with an input of 600w. The modulator uses 2 4012A valves driving a modulator consisting of two 4212D valves.
The receivers operate in a similar manner to the Brighton receivers. However it is a more complicated system with the transmitter modulated for a period of 30 seconds by a tone of 4Kcs which causes the call lamp on the receiver to light rather than being carrier operated and is effectively a paging system only responding to the modulated tone as opposed to any carrier being received and possibly suffering false activation of the call indicator by an interfering carrier. Four receivers were in use 3 on motorcycles and one in a car.
Stockport Borough police radio system call sign GTS
This was again a one-way radio system operating on 2050Kcs 146.8mtrs. The system is described in Post office technical report TCB226/254. The equipment was supplied and maintained by Hollingdrake & sons Ltd having been built for them by Dubilier of Acton. The transmitter is crystal controlled and the oscillator uses an LS5B valve feeding an amplifier using a Mullard DO40 valve.
The receiver is of a three valve super regenerative design made by Gent of Leicester. The first stage being screen grid valve, acting as both detector and quench oscillator. This is followed by two stages of LF amplification. The receiver operates in a similar manner to the Brighton receiver and a calling lamplights when a transmission from the transmitter is made. The officer switches the lamp out of circuit and an earpiece, similar to the Brighton one, is used to receive the broadcast. If the officer is away from the vehicle a bell can be switched into circuit to call attention to a transmission being made.
By 1935 it was found that further frequencies were needed to avoid interference between stations and a new frequency plan was in place.
FREQUENCY PLAN 1935
It was reported in the Glasgow Herald in August 1936 that Lancashire Police had police horse Sammy fitted out with a wireless set and had a call sign of GTL9, this was intended for traffic control and the equipment had a range of about 3 miles.
In 1937 Aberdeen city Police MXM introduced two bicycle patrols with receivers
As things progress towards the late 1930s and the second world war which was to break out in 1939 indications are that people at the Home office and the Post office in 1938 were already considering how war would affect the use of police and fire radio systems and the Home office frequencies. The Home office for police use asked for frequencies between 30 and 32Mcs, but these were already earmarked for air defence purposes. Eventually two spot frequencies were allocated for use of provincial towns on 30Mcs and 31Mcs. However trouble was experienced in finding frequencies in this range for use in London that would not interfere with the Royal Air Force allocations. While this might seem strange now, the channel spacing between frequencies at this time was at the very least 100kcs giving ten channels per Mcs and receiver technology was such that even at this spacing interference was experienced between stations which were close together. So for a given area only five or six channels could be used per Mcs. I can find no reference in official documents to the 30Mcs and 31Mcs frequencies actually coming into use at any location.
The Metropolitan police had a 60Mcs link between New Scotland Yard and West Wickham but this was on what was effectively an unlicensed frequency having been tried as an experimental link when licenses for frequencies above 30Mcs weren't needed, it seems to have just been left in place.
Following the Cairo radio conference in 1938 further changes to police and fire medium frequency allocations were needed due to international frequency allocation changes. Proposals were then put forward to have a regional police wireless service.
INITIAL REGIONAL STATION SCHEME
HOME OFFICE FREQUENCY PLAN 1938 POST CAIRO RADIO CONFERENCE
HOME OFFICE FREQUENCY PLAN 1938 POST CAIRO RADIO CONFERENCE
On the outbreak of war in 1939 it was recognised that there would be a need for wireless links in the event of damage to telephone and telegraph lines by bombs. Frequencies at 95.5-100Mcs, 128-131Mcs and 250-255Mcs were earmarked with the possibility of frequencies at 78.5-82Mcs also being available. As it was the allocation at 95.5-100Mcs and 78.5-82Mcs was taken up and started to be used for Local police and fire schemes with early experiments in Brighton using GEC and Stratton (Eddystone) equipment.
There were a number of forces experimenting with Ultra short wavelength systems and some local schemes had been put in place. With Ultra short wave schemes in Liverpool, Manchester, Lancashire, Glasgow, Edinburgh and Aberdeen.
The Metropolitan Police introduced a VHF system to link divisional stations with West Wickham in case telephone lines were damaged. This operated at 79.8Mcs and 80.5Mcs split frequency. There was also another back up link between NSY and West Wickham on about 128mcs and 131Mcs this replaced the irregular 60Mcs link, which was discontinued. Link experiments were also tried at the higher frequency of 250Mcs but considerable fading was experienced even on line of sight links, which caused consternation, as there was no cause known. Consultation took place with the National Physics laboratory and the Post office with the thought being that the likely cause would be atmospheric moisture or precipitation. These were early days of VHF use and propagation characteristics were still largely unknowns and development and use of these frequencies were at the forefront of technology.
As a result of the advances in technology at Ultra short waves (VHF) The Post office was commissioned by the Home office to carry out wireless coverage tests at sites throughout the UK. The initial criteria for the use of VHF in local schemes, was in towns and cities with populations above 100,000 with the possibility of extending this to towns of 75,000 and then 50,000 if it proved viable. The trials took place on 80mcs and 95mcs with a few extra trials at 130mcs, using a 100W base satation ande 7W mobile station. Some of these trials included fire stations and the London Fire brigade. Specific tests were carried out at Liverpool and Southport with the Liverpool police to test radio equipment on a motorcycle. A Royal Enfield 1140cc side car combination was used for these tests. The results of the test showed that the reception was about half of that of a similar car installation and the recommendation was that it would be better if a small car was used instead of a motorcycle. The results of the tests over the whole of the trial were generally satisfactory. Listed below are the test areas and a location map. The areas shown correspond with the Home defence Commissioners regions as it was envisaged that the police network would be used to supplement line communications in the event of bombing of the telephone system and the Metropolitan Police, Glasgow Police and Manchester Police had link stations at 128-132Mhz installed.
During the mid part of the war about 1942 due to the increased use of wireless by police forces and fire brigades some difficulties were experienced with call signs. The three letter call sign format used by police and fire, were also used by other government stations and they were quickly running out. A review was carried out and the post office decided to allocate M2AA-M2ZZ and M2AAA-M2ZZZ with the convention that M2AA would be a Main station with M2AAA-AAZ being outstations of that main station and Mobiles being suffixed with a number. Given the sharing of the frequency with the fire service it was suggested that fire brigades Use numbers from 50-99 and Police forces use number from 10-49. However as the system of call signs developed and the National Fire service came into being Call signs for fire service use were allocated in the M2FA to M2FZ range. The callsigns were allocated round the regional station call sign, which was in the form of M2R and a letter. The letter then became the letter for police force call signs in that region. For instance M2RY Romsley regional station Birmingham. Police forces in area M2YL Birmingham, M2YH Staffordshire.
The committee to report into Police use of radio
With the rapid development in the use of radio by the police during the early part of the war the Home Office decided that there was a need for a coordinated approach to this development. Up until then, while the Home Office took an overview of developments and shared practices between forces. Forces were very much independent in how they developed and used radio. Licences were issued by the Post office and call signs once the change was made from 3 letter calls to the M2 series were allocated by the Home office.
The committee was formed in 1945 and headed by Sir Arthur Dixon of the Home office. The reason for the enquiry was the criticism being levelled at the Home Office by a number of Chief Constables. The original purpose of the Home office regional scheme was a one way system covering all parts of a region. To pass information to units from other sources and to direct resources, two way communication was not regarded as essential by the Home Office. With the introduction of local schemes on VHF it was found by Chief constables using these schemes that two way communication was satisfactory and indeed the coverage given was better than the regional MF schemes and was less noisy. While there was Representation on the committee by Scottish Home department and Scottish chief constables this was on an informative basis only with the report by the Home office aimed at police forces in England and Wales, Scotland by this time were firmly moving in the direction of VHF schemes. The VHF schemes in use were of AM modulation and using single frequency simplex. Except for 2 schemes, the one in Birmingham, which was a duplex system and one in South Staffordshire, which was FM. Many of these schemes were shared between Police and Fire brigades. The MF scheme was deemed to have a number of failings, the small number of frequencies available meant channels had to be reused and therefore there were interference issues, the regional areas could not be fully covered for effective telephony use, particularly in regard of two way working. It was discussed with the post office and it was suggested that the issues could be overcome by adopting single sideband suppressed carrier modulation, which would double the channels available and giver an equivalent 4 fold increase in power and therefore better coverage. However this would require expensive modification to the transmitters and also replacing all the receivers in the scheme. But there was no garuantee that this would make the MF scheme workable. A series of tests was carried out by the Post office into the Home office MF schemes this was based at the Chevely regional wireless station and three transmitters were used. The standard Post office design for the Home office at 450watts. A Marconi SWB11 adjusted to 3Kwatts and the SWB11 adjusted for 6.5Kwatts using a frequency of 2626.5kcs and it was found that no more than 66%of messages could be received more that 33 miles from the transmitters. Indications were that to provide sufficient coverage on the 2Mcs medium frequency channels with radio telephony it would require a power of 10Kw and this was deemed unacceptable from the post office. From this a decision was made to move all Police and fire radio systems to VHF but in the meantime keep the MF stations going until the transition was made.
MARCONI SWB11 from http://jproc.ca/ The radio pages of Jerry Proc VE3FAB
The VHF scheme envisaged up to 2 base stations per scheme operating on two frequencies and there being one mobile frequency per scheme with a view to minimising mutual interference difficulties. The Home office and Lancashire Police carried out trials in Berkshire, Buckingham and Oxford using AM. A trial was carried out using FM but it was found that there was an area roughly equidistant from the two base stations where there was very unsatisfactory reception. A further proposal was based on Research by the Post office of a scheme where the carriers would be spaced 20khz apart. A trial using this system was set up using base stations spaced 20 miles apart and it proved to be satisfactory. In straight trials between simplex AM and FM, FM was found to be less prone to interference and to provide a more consistent signal across and area but there needed to be a squelch system in the FM set due to the higher noise levels and this extra complexity and need for adjustment in the radio meant that FM although provided better coverage in simplex systems was not adopted as the standard of modulation. Although Lancashire and Birmingham City opted out of the Home office scheme and retained FM. Birmingham until the force amalgamations in the 70's when it became part of West Midlands Police and Lancashire right up until the adoption of Airwave. The Metropolitan police also opted for FM following trials in the capital.
A double frequency scheme was recommended on the basis that it would permit frequency reuse without risk of mutual interference. This was a significant consideration because post war the Home office was to lose the 128Mcs-131Mcs frequency band but this was offset to a degree by expanding the 95.5Mcs-100mcs band to 94.5Mcs-100Mcs. The separation of stations was 60 miles between the boundaries of schemes on the same frequency and where the frequencies were separated by 200kcs this may be reduced to 10 miles between boundaries.
The report recommended an initial area scheme with 21 areas. Some of these already had separate schemes working and which would remain.
The cost of providing the VHF scheme of 25 main stations, 50 satellite stations, 1650 mobile stations, 115 transmitters to convert existing receive only stations, 400 receive only stations and to include spare equipment installation and infrastructure was estimated at �475,158.10. In 2014 this would equate to �17,882,856.92.
This heralded the VHF telephony era and shaped the way police communications developed through to the late 90's and the introduction of the Airwave system. The other major development came along in the 60's with the introduction of the personal radio system at UHF.
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D. J. MCKAY G1JWG 2014