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.

 

Constructive comments and input are very much welcomed; such comments can be added at the foot of each page by subscribed readers.  Should you find that you do not have the necessary permission to add comments, please click the link at the top right of the page which reads "To join this workspace, request access".  Alternatively, the workspace owner can be contacted via the "Contact the Owner" link at the foot of the workspace frame. 

 

The wiki principle of multiple-authorship applies to this document and appropriate persons may be given write access to add to the wiki.

 

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...