Preface
This Wiki was started in 2012 to help document the long history of the Marconi Company in Broadcasting.
It has been private since its inception with access being limited to ex-employees of the Marconi Company or one of its sister companies.
The information contained within this Wiki is extensive and has been provided by many volunteer contributors. Its creators believe 2017 is now time to make it public. This will not only open it up to public scrutiny but also increase the opportunity for further input from an additional base thus increasing its credibility.
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This wiki is one of a series recording the history of the Marconi Company from its formation starting from Family
Statement of Intent
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"The Marconi Company during the 1920s was one of the most exciting places in the world to work."
Peter Wright
The centenary of the most significant event in this period is being celebrated with a series of events - see details here
Update - unfortunately due to the coronavirus outbreak many events were either postponed or cancelled or in cases where possible mounted online - see recordings here
Foreword
This was the first transmitter built by Marconi and used by him on his estate in Italy. The Italian government at first refused to support his work and he was financed by the British Ministry of Posts (Marconi's mother was British). His successes apparently convinced his own government and in 1903 he continued his work aboard the royal Italian yacht Carlo Alberto, loaned to him for the purpose of carrying out radio transmission experiments at sea.
Reference: http://www.ee.umd.edu/~taylor/marconi.htm
The end of the first world war in 1918 saw Marconi return to civilian management and start in earnest designing a new range of high power telephony transmitters. Almost by coincidence, the future of British radio broadcasting arrived in an ex-army wooden hut parked on the edge of a large partly flooded Essex field in a place called Writtle. Its call sign was simply 2MT.
Reference: Marconi's New Street Works 1912 - 2012 by Tim Wander
Introduction
Marconi were truly pioneers in the field of broadcasting, and as early as 1920, were operating a service from their Chelmsford factory. These activities directly resulted in the formation of the British Broadcasting Company which later became the world-famous British Broadcasting Corporation (BBC). The American Marconi Company played a prominent part in the development of the numerous commercial broadcasting stations in that country. It was subsequently taken over by the American Government and re-named the Radio Corporation of America.
Since the early days, the Marconi Company has completely engineered, supplied, and in many cases operated, broadcasting systems throughout the world; transmitting on long wave, medium wave, short wave, VHF and UHF. The Company was very closely associated with the development of television in the 1930's and it was the Marconi - EMI system which was adopted by the BBC in 1936 for the first public television service in the world, thus becoming the foundation of modern television broadcasting practice. Marconi's are also continuing to improve their range of NTSC compatible television equipment, the reliability and quality of which have been verified by years of service in closed-circuit applications.
Extract from the 1952 Marconi Catalogue
Equipment for paralleling broadcasting transmitter can be supplied. In this connection, a new system has been evolved which overcomes the defects and disadvantages of previous methods. An isolating circuit is used, which, whilst presenting substantially infinite impedance between the transmitters, allows the output signals to pass into a common load. Transmitters operating in parallel offer the distinct advantage that continuity of programme is assured since, should one transmitter develop a fault, the remainder will still radiate the programme and the fault can be cleared without programme breakdown. Such a system may also be arranged for operation at half power, resulting in a high efficiency. This new technique is embodied in the transmitter radiating from the Third Programme of the BBC at Daventry with great success. Complete aerial systems can also be supplied.
Extract from the 1964 Marconi Catalogue
Marconi broadcasting transmitters have been giving reliable service throughout the world for nearly 40 years. The Marconi Company pioneered radio broadcasting and, in fact, inaugurated the world’s first wireless telephony service as early as 1920.
Since these early days, this Company has built the majority of the high-powered transmitters supplied to the BBC, both for local and overseas services, and many broadcasting authorities throughout the world have been supplied with a great range of both transmitting and studio equipment. Many ‘turnkey’ projects have been completed where Marconi’s have been responsible for the entire contract, from site clearance to handing over the buildings complete with operational equipment. These form an important part of this Company’s business. Recently, contracts have been obtained in Ghana and Kuwait for the provision of 100kW transmitters, which have been installed complete with buildings and the provision of all other facilities required. These have been followed in the past year by a further similar contract in Ghana for 10kW and 250kW transmitters, 250kW transmitters are also being supplied in quantity to the BBC.
The range of transmitters featured at this time has been with emphasis on operational simplicity. The transmitters are simple in design but nevertheless include all the necessary facilities and protection against supply surges. For maximum reliability two transmitters are often employed in parallel. Equipment to provide this ‘active standby’ system is both simple and reliable.
The VHF transmitters all use the Marconi frequency-modulated quartz (f.m.q.) crystal oscillator system of modulating the transmitted carrier.
Continuous improvements in Marconi broadcasting transmitter designs have resulted in increased efficiency and reduced cooling requirements. Extensive experience in a variety of climatic conditions ensures that this equipment will provide reliable service in climates ranging from arctic to tropical.
Extract from the 1965 Marconi Catalogue
The full introduction in this catalogue is available here.
Extract from the 1980 Marconi Catalogue
Marconi has been designing and manufacturing broadcast transmitters for nearly 60 years. It is one of the very few companies who still produce transmitters for all broadcasting applications covering long, medium and short waves, Television Bands I, III, IV and V, and FM Band II.
Our staff consists of long service members reinforced by young and active newcomers, so new ideas and techniques are put into practice temprered by experience. This combination provides equipment of modern design and high reliability incorporating many major innovations.
Since providing the transmitter for Britain's first sound radio service in 1921, Marconi have supplied sound transmitters to over 100 countries. These range from 2.25MW for superpower operation down to 10W VHF FM transposers.
Extract from the 1984 Marconi Catalogue
Marconi supply AM broadcast transmitters covering the long, medium and short wavebands, together with FM transmitters for Band II monaural or stereo. Television transmitters cover all internationally recognised standards, colour or black and white, throughout Bands I, III, IV and V with output powers ranging from 2.5W to 55Kw are also standard supply.
We have designed a generation of transmitters which take full advantage of modern electronic technology to simplify operation and maintenance and providing exceptional efficiency and reliability. Modular systems are used and self-contained transmitters minimise installation requirements. For high power combining networks the 'Rotamode' filter offers considerable space space saving without loss of efficiency.
Containerised television transmitting stations, which are tested before leaving the factory, provide fully operational stations in the shortest possible time. All that is required on site is a concrete hardstanding and the connections to external supplies and an antenna. Some transmitters can be offerred as fully mobile systems, including power geberation, antenna and programme facilkities.
For further details of the Marconi capability in all their market areas please click here.
Index
Please select the area you would like to explore.
Other readings
Broadcasting Division (1969) click here
To view the Marconi organisation responsible for these areas in 1964 click here, and in 1984 click here.
There is a comprehensive listing of all Company publications to be found here
Support Services
To view the support services provided by Marconi in 1984 click here.
Snippets
Good news on the heritage front - a new manifestation of a restoration activity - Broadcast Engineering Conservation Group - working mainly on television outside broadcast vehicles.
An interesting compendium of broadcasting history
A bit of nostalgia
These comments were made on the original appearance of this snippet
Originally Posted by PaulM View Post
...The two transmitters are Marconi B6042 units using the highly efficient 'Pulsam' technology. ... the Pulsam technique is so important as it saves an awful lot of money in electricity bills!...
The transmitters are still Marconi B6042, but in point of fact they haven't been Pulsam for the best part of fifteen years, now. The Pulsam modulators (rather temperamental devices) were replaced by Continental switched-mode modulators, which are even more efficient (and all soid-stae, to boot). In later years, Dynamic Carrier Control was implemented on these units, to save even more power - effectively this is 'downwards modulation' where the peak carrier power remains fixed (at 250kW per unit) and the mean carrier power reduces with increasing modulation depth: these units now consume less power from the mains when they are 100% modulated, than when they are just radiating plain carrier - an interesting phenomenon.
So with regards to valves, each unit now only uses one 'large' valve (I think 250kW from one valve can count as large) so surely replacements shouldn't be such a major item.
Ray Cooper is offline
Default Re: R4 LW to go eventually?
Quote:
Originally Posted by Ray Cooper View Post
In later years, Dynamic Carrier Control was implemented on these units, to save even more power - effectively this is 'downwards modulation' where the peak carrier power remains fixed (at 250kW per unit) and the mean carrier power reduces with increasing modulation depth: these units now consume less power from the mains when they are 100% modulated, than when they are just radiating plain carrier - an interesting phenomenon.
Ray:
You're right in saying they implement DCC, (sometimes called AMC or Automatic Modulation Control). But I don't think the domestic BBC LF and MF transmitters ever used such an aggressive characteristic? (6dB was used for some HF services). The "norm" is to use 3dB carrier cut-back at peak modulation, so the peak power reduces from +6dB on nominal carrier (2000kW) to +3dB (1MW). The DCC/AMC time-constants are set to align with the agc time-constants used in most AM receivers: this results in a "re-expansion" of the compressed audio in the receiver. It's a very elegant system, and saves shed-loads of money & green-house gasses.
John
John_BS is offline
What were the mod. valves, Ray? TH555's? We once enqured after the cast-off 'grid-boxes' (modulator valve switching units) for Skelton, but they'd gone. Incidentally, we still use PULSAM - and AMC (6db compression) at Skelton, using TH555 valves to switch the PWM.
Rampisham got shot of their modulator valve switching units on the B6127's some years ago, replacing them with solid-state modulators, and we got those.
Shortwave in the UK is hardly a suitable barometer of future high-power broadcasting, I may add...
Broadcasting Division Experiences - David Lewis and an addendum and picture from Andrew Fremont
My Time with Broadcasting Division
As a Technician Apprentice I was seemingly randomly assigned to departments so I accepted without questioning why or what they might bring. So In January 1965 I was assigned to the Broadcast Development Group at the new premises of Broadcasting Division in Waterhouse Lane. The section in question was the Thin Film Research Lab which meant nothing to me until I had started working there.
The section was run by a white coated lady called Pat Chapman (if I remember correctly) and the Group Leader was a fatherly figure called Ernie Holland. We had two rooms, one was something of an office and the other the lab itself. In the lab one wall was taken up by a white panelled equipment bench and control panel with an area resembling a fume cabinet in a chemistry lab.
My first task on arrival was to construct a second set of equipment to compliment the first one. The whole thing was built around a vacuum system which involved three stages of pumps to achieve a very high vacuum in a bell jar that was about 18 inches tall and 12 inches in diameter, more of which later.
To build this involved using “Yorkshire” capillary plumbing fittings and domestic style copper piping. When assembled I had to test the system by pumping down the vacuum until the vacuum gauge stopped moving, then systematically smear silicon grease on each joint until the vacuum started increasing again. Having located the suspect joint I had to shut down the system and then remake the joint to be airtight which seemed to be more difficult than water tight! I then moved on to the more familiar task of wiring the various subsystems and displays to complete the rig.
Inside the bell jar location there was a circular baseplate with a series of insulated high current terminals, above which there was a circular structure with a fixed level disc and above it a movable disc which was able to be raised and rotated whilst the bell jar which covered everything was in place and at the required vacuum.
The upper disc had a number of positions to accommodate the placement of matchbox top sized glass substrates. The fixed disc beneath had corresponding positions which would hold similar sized etched copper masks.
The high current terminals below were used in pairs to accommodate the various elements to be evaporated. A pair would be fitted with a Tungsten spiral into which a number of small lengths of Nichrome wire were placed. Another pair would have a boat shaped piece of Molybdenum which contained pieces of Gold wire.
There might have been another substance as a pacifying layer but my memory is not sharp enough!
In operation, the metals to be evaporated in the terminal connections were put in place, the etched copper masks made, placed, and finally the glass substrates cleaned with isopropyl alcohol and put in place.( I had to use cotton gloves to ensure cleanliness)
Finally the bell jar was put in place over everything and the system pumped down to the high vacuum needed. This took some time as the final stage was an ion diffusion pump which takes time to achieve its effect.
When the desired vacuum was achieved the control for the current through the Tungsten spiral was operated for a set time causing the Nichrome to evaporate and coat the exposed areas of the substrates.. Then the upper disc inside the jar was lifted and rotated to its next indexed position. This put the substrates over a different mask. The current was then passed through the Molybdenum boat causing the Gold to evaporate and coat the new exposed surfaces of the substrates. ( My recollection of the sequence is a little hazy as I particularly remember when the Gold was evaporated there was a moment when there was an amazing golden glow from the bell jar before the metal vapour “silvered” the internal surface and obscured further viewing.)
The vacuum was now released and the substrates removed and checked. The Nichrome tracks on the substrate formed resistors and the Gold areas connecting pads. My task was then to solder two TO18 RF transistors onto the gold pads on each and then connect them to a small strip of printed board which was to form the base of the enclosure in which they were put. The enclosure I had to fabricate from thin sheet copper and the resulting package was perhaps a little thinner and longer than a matchbox.
The resulting circuit was a twenty dB amplifier intended for use in colour TV cameras which were under development elsewhere in the building. It seems by constructing them in this way they would have a very good behaviour with temperature but more importantly their behaviour with temperature would match in the different colour channels involved and not cause colour distortion in the final images.
Another task that I had was to assess the mechanical reliability of the modules. In order to do this I would take a tested good module up to the top of the stairs at the end of the building and drop it down the stairwell. I then checked its operation. There were a large number of failures which were caused by the transistors pulling out of the soldered joints on impact. It turned out that the gold plated leads on the transistors formed a physically weak alloy bond with the solder causing this to happen. We changed the transistor supply for ones with tinned leads which eliminated the problem!
Sometime during this period the official opening of the building occurred and was attended by luminaries of the time; I only remember a young Judith Chalmers who was already popular on TV. I also remember talking to someone who may have been a BBC cameraman. He recalled to me the difficulties he encountered during the filming of Winston Churchill’s funeral; it seems that the cameras at the time (possibly MKIII) did not like the cold up on the rooftops and had to be covered up in blankets to keep them warm to ensure a stable picture. This made me more understanding of what we were doing in the lab!
I was then re-assigned to the test section to work for a charismatic/eccentric section leader I only recall as “Bill”. He had a habit of punctuating words with expletives like bloody. Working there seemed to be mostly on high voltage bits of gear instructed “to keep one hand in your pocket” for safety reasons.
One day he surprised and baffled me when I was supposed to be constructing a transistor amplifier for something. He gave me, without explanation, other than “try this”; a device in a TO5 can with eight leads instead of three, and a triangular circuit symbol I had not seen before. It was an early operational amplifier!
In October I was re-assigned to the Semi-conductor Physics group at Baddow and left what was one of the more memorable and interesting periods in my apprenticeship.
I would love to hear from anyone who remembers that period especially whether those modules went into production colour cameras!
Comments (2)
Alan Hartley-Smith said
at 1:53 am on Jul 28, 2017
Test comment as agreed
Ian Gillis said
at 1:57 am on Jul 28, 2017
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