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Initially, it commenced transmission in Morse code on 16kHz with an aerial power of 350kW. At the time it was the world's most powerful transmitter using thermionic valves.
Later in the 1926 two-way conversation by radio telephone was also established for the first time between England and the USA from Rugby (on 60khz with an alternate 68kHz)) with inauguration of the Transatlantic Telephone Service in January 1927. In August 1928 short wave frequencies for used for telephony. Later cables and satellites would take over. There were twelve 820 feet masts each weighing 200 tons.
From 1951 Rugby was used to transmit coded signals to "wireless clocks" initially on short wave with an hour on 60kHz. In 1966 60kHz was used for a 24hr time signal. ("MSF" transmitter on 60kHz)- the contract expired in 2007 and was awarded to another supplier located elsewhere who does not operate 24/365 but is cheaper.
Very long wavelengths are also of value for radio communication with submarines and this was the third use of Rugby.
In 2004 eight masts were demolished.
THE new Rugby radio station, which is now rapidly approaching completion, will provide a means of communicating with the most outlying parts of the British Empire throughout all periods of the day and night. In power it will greatly exceed any other station in the British Isles and will be unsurpassed by any station in the World.
The selection of a suitable site for a large wireless station is always a difficult matter, and in the case of the Rugby station these difficulties were increased by the size and special requirements involved.
The site lies about four miles south-east of Rugby, near the village of Hillmorton, in the extreme south- east corner of Warwickshire, and comprises some 900 acres, or approximately one and a half square miles of land. It is situated on level ground and bounded on one side by the Watling Street and on the other side by the Oxford Canal.
The station buildings are erected approximately in the centre of the site, and the twelve masts are disposed around it. The masts, which are 820ft. high, were constructed by Messrs. Head, Wrightson and Co., Thornaby-on-Tees, and are of lattice steelwork, having a triangular cross~section of 10ft. side. Owing to their large cross-section, the great height of the masts is not immediately apparent, and can only be thoroughly realised by a trip to the top.
The masts are each supported by fifteen steel wire rope stays arranged in three groups of five stays, each stay being attached to a concrete anchor block through an insulating device at its lower extremity.
The lower end of the mast tapers to a point, below which is a ball and socket joint. The purpose of this joint is to allow the mast to move under the load of external forces such as wind load and antenna pull - without throwing strain on the foundations. Although each stay is initially tensioned to several tons pull, yet under the stress of the heaviest winds and the application of the antenna load, which is of the order of 10 tons, the top of the mast moves several feet.
Beneath the above-mentioned ball and socket joint is an insulating layer of porcelain blocks, and beneath these
is another insulator consisting of granite blocks. Arrangements are made to enable the porcelain blocks to be changed in the event of breakage, and, in fact, during construction temporary wooden blocks were used, the mast afterwards being bodily lifted by hydraulic jacks to permit the insertion of the insulators.
The granite blocks are in turn supported from the foundations by a short steel column. A platform is erected on the mast about 33ft. above the ground, on which is placed the electrically driven winch (See photo).
The space inside the lattivce mast is occupied by a steel ladder and a small lift cage, both of which run from top to bottom of the mast. The ladder is protected by steel hoops every few feet. These serve two purposes: they provide an additional sense of security and prevent a climber being knocked off in a wind by a swaying rope.
The electric lift, which holds three persons and takes twelve minutes to complete its journey, is provided with the usual safety devices to prevent accidents due to over-winding or failure of the lift rope. The provision of a lift on each mast might at first sight be thought an extravagance; actually, however, they effect an economy, as, in the event of aerial overhauls being necessary, the loss of time involved in men climbing the masts would be prohibitive, and in heavy winds it would lead to prolonged stoppage.
The masts are placed exactly a quarter of a mile apart, and will support antennae of cage or sausage type of about 12ft. diameter.
In view of the danger to aircraft, arrangements are being made to provide powerful navigation lights on the tops of some of the masts situated at the remote ends of the site.
The station buildings consist of two blocks- the wireless block, and the substation and is connected thereto by offices and retiring rooms.
The earthing system contains over 100 miles of wire which, over the greater poftion of the site, has been buried beneath the surface.
This operation was rapidly carried out by means of a specially built plough on which was mounted the drum of wire. The plough was drawn by a motor tractor and laid the wire in one operation.
The main transmitting building consists, in effect, of three floors. On the ground floor are situated the valve panels and control gear; above this will be mounted the condensers. Above the condensers again will be placed the huge inductance coils, some of which will be 16ft. in diameter, wound with cables consisting of over six thousand separately insulated wires.
The valve equipment will consist of two separate transmitters, a telegraph transmitter capable of dealing with from 500 to 1,000 kilowatts, and an experimental telephone transmitter giving an antenna input of 200 kilowatts. Some idea of the power of these sets will be realised when the reader is reminded that the power of local broadcasting stations is about 1,500 watts, while the power of the Chelmsford broadcasting station is about 25 kilowatts.
The valve transmitter will be controlled by a steel tuning fork which will be maintained in continuous oscillation at about 2,000 vibrations per second by means of a small valve. By means of apparatus recently developed by the Post Office, the current oscillations produced by this fork are extremely rich in harmonics. By means of suitable filter circuits one of these harmonics is selected and amplified in several stages. This harmonic, after amplification, will be applied to the grids of the main transmitter valves. As the frequency of the tuning fork is remarkably constant, the frequency of the transmitter, which is a multiple thereof, will be equally constant.
The experimental telephone transmitter will operate on a system developed by the Western Electric Company in which the carrier wave and a portion of the signal usually radiated is suppressed. As a result, the signal actually radiated, with a certain aerial current, is equivalent to one of much greater power radiated by the ordinary type of wireless telephone transmitter, and yet causes considerably less interference on adjoining wave-lengths.
The scheme also possesses another advantage, namely, that without special apparatus it is extremely difficult, in fact practically impossible, to obtain understandable signals on an ordinary receiver, This gives a certain element of secrecy to the transmission.
The telephone transmitter is being installed for experimental trials in Trans-Atlantic telephony, in co-operation with the American Telegraph and Telephone Company, and a special receiving station for the American traffic is being erected near Swindon, Wilts.
The valves used on both telegraph and telephone transmitters will be of the wate-cooled type, and will be cooled by a supply of distilled water which will in turn he cooled by means of water circulating from a pond constructed on the site.
The power supply to the station is being obtained from a public supply, and duplicate mains have been provided to minimise the risk of supply failure. As received it is an alternating three-phase supply at 12,000 volts pressure, and is led to a high tension switchboard for distribution to the various transformers, which reduce the pressure to 416 volts for all auxiliary machinery and to 2,200 volts for the main motor generators.
The main generators consist of three motor generator sets of special design, manufactured by the British Thomson-Houston Co., of Rugby, each set having an output of 500 kw. at 6,000 volts D.C. As these sets can he connected in series, it is possible to obtain a supply of 1,500 kw. at 18,000 volts D.C, for the anodes of the transmitting valves.
The motor generator sets are each located in a screened enclosure, and an ingenious system of electrical and mechanical interlocks ensures that these enclosures cannot be entered while the apparatus is alive.
Each motor generator set and its control gear is mounted on insulators, and all controls are effected through the medium of insulated rods.
As there is considerable likelihood of a short circuit occurring inside a valve when the filament burns out, special steps have been taken to provide for this event. High-speed circuit breakers are arranged to operate within a thirtieth of a second after a short circuit, and to insert a blocking resistance in the circuit to prevent excessive current flowing.
As may be imagined, the filament supply to such a large valve transmitter will absorb a considerable amount of power. It is extremely important that such a supply should not be subject to fluctuations in voltage, and to ensure that this does not occur the filament supply is obtained from alternators driven by synchronous motors, each alternator having an output of 200o KVA at 416 volts 100 cycles.
As an additional precaution, special voltage regulators are fitted to the alternator to prevent fluctuations in pressure which might occur, due to switching or to variation in the supply frequency.
To ensure continuity of supply for control circuits and to provide an independent source of lighting, a small secondary battery is being installed which will be charged by motor-generator and booster sets.
As may be imagined, the construction of a station of this magnitude entails a vast amount of work of specialised character in many branches of engineering. Structural, hydraulic, electrical power and radio engineering have each of them their special problems which call for solution, and in each subject it usually happens that these problems require an extension of our present knowledge of the subject.
In consultation with the Wireless Telegraphy Commission, consisting of Dr. W, H. Eccles, Mr. L. B. Turner and Mr. E. H, Shaughnessy, the designs have been fully prepared by the Post Office engineers, or detailed specifications have been prepared from which the manufacturers have designed some of the plant.
The completion of the station will bring this country in touch with all countries of the world, and will provide a means of communication with ships of the British Navy at all times of the day and night.
Detailed Description of the new high-power broadcasting station now nearing completion.RECENT work at Daventry has been very rapid and the station is well on its way towards completion. With practically all the apparatus installed, one mast completed and the other nearly finished the station should be in good order for the opening by the Postmaster-General on July 27th.
Details of the station have now been given, and it has been possible to secure some excellent photographs, taken a few days ago, of the layout of the station and apparatus. It is hard to believe that the work of building the station has been carried out in less than six months.
The site of the station, one of the highest points in the Northampton uplands, covers altogether about 60 acres, of which only a part is in use for the present station. It is interesting to note that it is built on the high ground called Borough Hill, the situation of an old Roman Camp, overlooking the ancient Watling Street- the road that the Romans built from Dover to Chester.
The buildings consist of a power-house, a small transformer building (these two are seen in the heading photograph, which is taken from one-quarter way up one of the masts), and quarters for housing the staff of six resident engineers.
The power house is over 120ft. long and 65ft. wide, and contains one large room for the transmitting set, a generator room, amplifier room, workshop, two offices, and also a small test studio, which will he draped and furnished in a manner similar to the studios at 2, Savoy Hill.
The masts are of the lattice type with triangular section, and are 500ft. high. They are each supported by three sets of guy ropes; spaced at 120 degrees, and are mounted on steel bases with very solid concrete foundatious.
As the ground is 650ft above sea level, the tops of the masts will actually be 1,150ft above the sea. On the top of each mast is fitted a warning light for aircraft, the glass dome covering four electric lamps, and these are flashed according to a prearranged code by means of`a motor contact-maker.
The aerial is of the T- type, the horizontal part consisting of six wires spaced by hoops 6ft. in diameter, with a similar lead-in. The span is ahout 600ft.
The earth system consists of a ring of zinc plates 200ft. in diameter round about the power house. The ring of plates is clearly shown in the heading photograph, and radial connecting wires from these plates, are brought to the insulator seen on top of the roof of the power house. The lead-in from the aerial is also brought close to the same point.
In addition to the main earth, there is a buried earth underneath the power house, and to this is earthed the frames of the machines and transmitting apparatus.
An Efficient Radiation System
With this type of aerial and earth, especially as it is situated on such high ground, as very efficient radiation system has been obtained, and with the set working at the same power as now in use at Chelmsford, signal strength at corresponding ranges should be greater from Daventry than from Chelmsford.
The power supply for the station is taken from the mains of the Northampton Electric Light and Power Co., at a voltage of 11,000, the supply being 3-phase A.C., and this is transformed down to 375 volts in the small separate building. The lighting of the station is taken from one phase at 210 volts
. For the transmitter itself; there are eight machines, each containing 3-phase induction motors, three of them being motor generators, and five motor alternators.
The motor alternators give a voltage of 1,000 at 300 cycles, and for the high-tension this is transformed up, giving a rectified voltage of 10,000. The machines are all conveniently controlled by one switchboard
The Transmitter Coming now to the transmitter itself, the design is practically identical with that of the Chelmsford station, with many minor improvements suggested during the running experience of that station, and various safety and stand-by devices are incorporated as are necessary for a permanent station.
The set is divided into five parts- the rectifiers, the drive oscillator, the main oscillator, the sub-control, and the control system.
All of these, except the sub-control contain water- cooled valves, and special arrangements have been made to ensure that the water supply for this purpose is more than adequate, as the consumption of water to keep all these valves cool is quite large.
It is interesting to note that the method of spraying the water into small tanks where it is led to and away from the anodes of ` the valves, keeps the anodes and their water jackets perfectly insulated.
The general lay-out of the transmitting room is shown in Fig. 3 . In the foreground in Fig. 3 is the speech transformer, each winding having an inductance of the order of 50 henries. To the right of this are the air core chokes. Behind, from left to right; the drive panel, the oscillator panel, the rectifier panel.
At the back the frames for the large air condensers (one plate of these is shown on end), and, to the right, the main switchboard of the set.
The power of the set will be 25-kW. to the main oscillators, but the motor alternators and generators are capable of dealing with more than twice this power, so that an increase of power could be obtained by the addition of extra valve panels. The wavelength of 1,600 metres will be retained. The wavelength will be absolutely constant as a result of the special rigid inductances in the drive circuit. Moreover, the large air condensers in the main high-frequency circuits are shielded and thus protected from interaction with other parts of the circuit.
Land Lines and Amplifiers
The transmissions from the Daventry station will emanate (like the Chelmsford transmissions) from London, the music being sent to Daventry over Post Office land lines, several spare lines being provided to avoid any possibility of a breakdown. There will be amplifiers at Daventry to amplify the music up to the strength required to operate the sub-control valves of the transmitter. Special amplifiers have been designed for the London and Daventry ends of the line to ensure that the least possible distortion is experienced, so that the quality of transmission from Daventry should be equal to that of London.
The present Chelmsford site is considered advantageous by way of providing an alternative transmission for listeners on the south coast when experiencing interference by ship and coast station jamming, and no doubts need be entertained as to the ability of the new station at Daventry to fuliil this requirement.
It appears that the transmitter has a very excellent layout, and when completed will be of very smart appearance, and there is no doubt that the Daventry station will be the finest and largest broadcasting station in the world.
If it maintains the quality of the transmission now sent out from Chelmsford, British listeners will have no reason for being anything but proud of the latest addition to the B.B.C.'s system of stations.
5XX was an experimental Long Wave transmission from Chelmsford from June 1924 to July 1925, after which the transmitter was in Daventry. 5XX was used for the first public stereo radio broadcast, acting as the right hand channel for a concert from The Free Trade Hall, Manchester, England as early as December 1925..
2LO was a medium wave transmitter from London, May 1922
to around 1925- the transmitter is now in the hands of the Science Museum London.
Long wave broadcasts of the National program from Daventry ceased in 1934 when the Droitwich transmitter was used, and continues (on a more powerful transmitter) until the last valve burns out. The 5XX transmitter was retained at Daventry as a standy by, until scrapped in 1949. Three water cooled valves survive on display at Daventry Town Council Museum.
Initial experimental short wave broadcasts were from Chelmsford on 5SW. Shortwave from Daventry commenced on Sender 1 and 2 (15kW each) from 1932, and in 1935 the 5SW transmitter was moved from Chelmsford to Daventry where it became Sender 3.
Daventry was used for most BBC Empire (BBC World) services, and the final broadcast in 1992 was of the BBC World Service on 19 metres. Daventry was also the base for the Third Programme transmissions on 464 metres from 1951. There is currently a DAB transmitter site in the town.
There has been a considerable speeding up in the work of installing the station during the past few months in order that it might be completed by the time specified, and, although it has now been formally opened, this is not, we understand, a guarantee that it will commence regular transmissions immediately, because, so far practically no time has been devoted to preliminary experimental transmissions which must be regarded as essential before guaranteed regular programmes can be put out.
It would not be possible to anticipate every difficulty which might arise after completion of such a station as this, which is the newest and probably the biggest station yet constructed solely for broadcasting purposes. It will be remembered that the transfer of the London Station, 2LO, to its present site was accompanied by considerable technical difiiculties, and, in fact, the station was not operating satisfactorily until recent weeks, and if the same behaviour is adopted by the Daventry Station this must not come as a surprise to listeners.
Criticism may be made from time to time of the policy of the British Broadcasting Company in the matter of the wavelengths and power of the stations and other matters of detail, but the progressive spirit which has been shown throughout the period since the B.B.C. was inaugurated is a matter which calls for admiration.
When we consider that from the very outset it has been entirely pioneer work with innumerable difficulties to surmount and fresh problems arising from day to day, one must recognise that a very large amount of credit is due to those who have been responsible for the building up of such an organisation.
The whole question of broadcasting is, as we have recently learned, to come up for consideration by the Government before the end of the present year. The question of whether there should be competitive broadcasting in this country is a matter which need.not be discussed here now, the object of the present note being to record the opening of the Daventry Station and to offer congratulations to the B.B.C. on their enterprise and the progress achieved.
It would be out of place to express appreciation of the work of the B.B.C. without coupling with it the name of the managing director, Mr. J.C.W. Reith, who must feel justly proud of the organisation which has grown up under his direction.
The temporary high power broadcasting station of the B.B.C. at Chelmsford, which has been in operation for over a year for research and development purposes, was replaced on Monday, 27th July, when the new Daventry station was opened by Sir William Mitchell-Thomson, K.B.E., M.P.
THE Prime Minister, in writing to the Managing Director the British Broadcasting Company on the occasion of the opening of the Daventry station, very aptly refers to the event as "another mile-stone on the road to the social betterment of our people."
The significance of this announcement may not be particularly apparent today, but those who may look back a year or two hence and recall these words will undoubtedly regard them as prophetic.
It was_in July, 1924 that 5XX first commenced transmissions as an experimental high power station located at Chelmsford, and now, in July, 1925, the permanent high power station centrally situated at Daventry has come into existence. The station was officially opened on July 27th by His Majesty's Postmaster-General, Sir William Mitchell-Thomson, K.B.E., M.P who together with the Chairman, the Managing Director, the Chief Engineer and other officials of the British Broadcasting Company, journeyed to Daventry from London with a large number of guests of the company who had received invitations to be present on this important occasion.
The opening ceremony took place before the microphone in the small studio which has been provided in the station building.
The opening of the station was the occasion for appreciation to be expressed by Lord Gainford, the chairman of the B.B.C., of the excellent relations which had always existed between the company and the Post Office ever since the inception of broadcasting, whilst Capt, P. P. Eckersley, the chief engineer, took the opportunity of acknowledging the work of the members of the technical staff of the B.B.C. and the various contracting firms who had been entrusted with the erection of the station.
The actual wireless equipment was supplied and installed by Marconi's Wireless Telegraph Company, whilst the contract for the masts and aerial equipment was given to the Radio Communication Co., who, in turn, engaged the services of Mr. C. F. Elwell for the design and construction of the masts. Mr. Elwell has been responsible for mast erection work at a large number of modern high power stations.
The Western Electric Co designed the special line amplifier, and co-operated with the B.B.C. and the Post Office in making possible the transmission of programmes from the London studio to the Daventrv station.
The Postmaster-General, in his address, commented on the question of the utilisation of broadcasting for the transmission of political speeches, and expressed the hope that, as far as possible, broadcasting might be kept clear of party politics and operate solely as a. national service.
For the B.B.C. to associate itself with political matters would, he thought, make the position in the future more difficult and hamper the policy of those responsible for guiding the destinies of the B.B.C. in a way which he considered would be regrettable.
Below we are able to publish various technical details of the equipment of the station which were not available until the date of the opening, together with some. additional photographs.
The masts are two in number, with a height of 500ft., and are placed 800ft. apart. They are of the stayed type; or iron lattice-work construction, and of triangular section.
Aerial System
The "T" shaped aerial is composed of a ten-wire cage along the horizontal portion, which has a length of 600ft., with a down lead consisting of a six-wire cage brought to an insulator and lead-in trunk placed on one of the roof ridges.
The earthing arrangements comprise a number of metal plates sunk in the ground and forming a ring round the building. A wire from each earth plate is led up to an insulator on a 15ft. mast, of which there are thirty eight disposed in a circle of 100 ft. radius from the aerial trunk, and then above the roof to a ring fastened round the trunk. From this ring a couple of copper strips are taken down inside the trunk to the earth terminals of the transmitter.
Such a system of earthing forms an electrostatic screen over the roof. and probably serves to reduce aerial losses to some extent.
The electrical power is supplied by the Northampton Electricity Supply Co, in the form of three-phase alternating current at 11,000 volts 50 cycles. This is transformed down to 375 volts at a substation on the site. It was thought undesirable to rectify the three- phase supply direct for supplying the valve transmitter, as any slight out-of balance load on one of the incoming phases might cause difficulty in maintaining the requisite degree of smoothing, so rotary machinery is installed to provide a local single-phase supply.
Although the present rating of the station is fixed at 25 KW., by which is to be understood the mean power input to the plates of the magnifier valves, provision has been made for a rating up to 6o KW; on the same basis as regards the machinery to meet possible future requirements. All transformers, chokes, cables, and high-frequency apparatus used in the station have been designed with sufficient capacity for dealing with this higher power when required.
The power plant consists of five 1,000 volt motor alternators, three 70-KW and two 25-KW. plus three 10-KW. motor generators delivering direct current at 20/30 volts. There are also a few smaller machines, such as motor pumps, etc .
Power Supply
Two of the 70-KW. machines are in use at one time, the third machine being a spare, one machine supplying power for the modulator valves,, and the other for the magnifiers. One 25-KW. alternator is run for supplying power to the drive oscillator, and also for lighting the filaments of all the rectifying valves.
The direct current motor generators are used for lighting the filaments of other valves, two of these being required, leaving one available as a reserve.
The design of the wireless apparatus has been based upon the experience obtained at Chelmsford with the experimental high power broadcast station 5XX, in fact, both stations are similar as regards the theoretical circuits. In the new station more attention has been paid to the appearance of the various units, and the control switching has been elaborated, with a view to securing greater convenience of operation and quicker repair in the event of a breakdown.
The wireless transmitting gear:
The smoothing circuits for a set of this size present something of a problem, as the permissible ripple is very small for high quality broadcast telephony, and the smoothing units are necessarily somewhat bulky and costly. The condensers for the smoothing system consist of zinc plates with glass dielectric, oil immersed in porcelain containers. The total capacity used on each half of the circuit is approximately 3.5 microfarads and the inductance about 16 henries.
The smoothing inductances are closed iron core chokes placed in oil tanks. Each choke contains about 5 cwt. of iron; and there are eight of these in all.
The arrangements made for water cooling the valve anodes deserve attention. As the anodes are at high potential it is necessary to insulate the valve water jackets from the main supply of water.
This is accomplished by running the water both in and out, of the jackets through spraying nozzles. The water spray forms an almost perfect insulator, and, therefore, no loss is sustained by leakage. The cooling water is stored in a concrete lined pond holding about 5,000 gallons, and is pumped from there up to a tank in the roof, falling by gravity through the valve jackets back to the pond.
The rate of flow is adjusted to allow about one gallon per minute through each valve jacket, and under these conditions the water leaving the valves is only increased in temperature a few degrees. As it is important to use cooling water free from lime or other ingredients capable of forming a deposit on the anodes, rain water is utilised, and arrangements are made to drain water from the roof into the storage pond, a rainfall of one inch giving about 1,000 gallons to the pond.
The apparatus for controlling the power input to the various sections of the transmitter is mounted on one control table placed in such a position in the apparatus room that the shift engineer at the control table has a clear view of the valve panels and the various indicating instruments mounted thereon.
On the control table are mounted the exciter field rheostats of all the alternators and dynamos, so that the machines can be brought up to the required voltage from there. Magnetic trip switches enable any particular machine to be cut out at quick otice if necessary, and a masterswitch is available which, opened, stops all the machines generating, except the filament lighting dynamos. The whole of the high tension wireless apparatus is enclosed by a metal railing, the gate of which has a safety switch to cut off power when opened.
The system of relays and wiring adopted renders it necessary to start up in a certain prescribed order of operations. The high tension voltage cannot be applied to the drive oscillator unless the safety gate is closed and the valve filaments alight, neither can the power be thrown on the magnifier and rnodulator valves until the gate is closed, all filaments fully alight, and the drive oscillating at approximately its correct input.
Also, if for any reason the drive should cease oscillating the set is automatically shut down. A wavemeter with visual indicator on the control table keeps the shift engineer informed as to the wavelength constancy, and can show half a metre variation from the correct value.
Even in such a rapidly expanding art as wireless telephony it seems more than likely that the Daventry station will serve as a model of what is desirable in a super broadcast station for several years to come.
The following is the text of a letter from the Prime Minister to the Managing Director of the B.B.C., written on the occasion of the opening of the Daventry Station
10, Downing Street, ,
Whitehall, S.W.1
July 21st, 1925
DEAR MR. REITH,
I confess to a feeling of keen disappointment at my inability to attend the opening of the new Wireless Broadcasting Station at Daventry.
It is not too much to say that broadcasting is already contributing appreciably to the happiness and knowledge of the present generation. The opening of the Wireless Broadcasting Station at Daventry - the highest powered station at present in the world- will give no fewer than twenty million people the opportunity to
receive both education and entertainment by means of cheap and simple apparatus; and I look upon Daventry as another milestone on the road to the social betterment of our people.
STANLEY BALDWIN.
BY BEAM TO AUSTRALIA
At 6 o'clock on the morning of April 8th (1927) the official beam wireless service was opened between this country and Australia.
On the previous day a preliminary demonstration was given in the Central Wireless Office of the G.P.O., and complimentary messages were exchanged between Mr. L. S. Amery, Secretary of State for the Dominions, and Lord Stonehaven, Governor-General of Australia, Mr. Bruce, the Australian Prime Minister, Mr. Hughes, and others.
The messages from London are despatched via land line to Grimsby, whence they travel 10,000 miles to the Australian receiving station at Rockbank, and from there via land line to Melbourne.
In the reverse direction signals travel from Melbourne, via landline to Ballan, whence they are transmitted to Skegness and conveyed by land line to London.
It is expected that the Indian and South African beam stations will- be ready for testing within a few weeks.
[By the end of the following year, the cable telegraphy business was suffering badly from the competition, and the cable and wireless operations within the Empire were placed under a single company, to become known as Cable and Wireless. The limitations of short wave radio propagation were not tested over a sufficient period to show up the limitations. 1927 was a fairly good year for short wave reception with a sun spot peak. Results would have been quite different in 1933 when the number of sun spots was hovering around nil.]
SHORT-WAVE TRANSMISSION ROUND THE EARTH
Sir,
In your issue of March 23rd, there is a brief note referring to the experiments recently made in Berlin to determine the time taken for a signal to travel round the world.
From this time the length of path is calculated, and thus the height at which the wave has travelled, is deduced.
The results obtained give a height which your Berlin correspondent gives as 550 kilometres, but which Herr Quack, of the Telefunken Company, states to be 182 kilometres.
Now these results are based on the assumption that the waves travel with the velocity of light in vacuo, but since the waves travel in an ionised medium they have a phase velocity higher and a group velocity lower than the velocity of light. Since the waves travel around the earth their phase velocity can be estimated, and from it the group velocity.
Making this very necessary correction, the German observations are consistent with a height of about 90 kilometres, which agrees very well with the height deduced from other experiments.
I had already written an article discussing this point in detail, which article will appear in the May number of Experimental Wireless when the note in The Wireless World suggested the advisability of pointing out at once that the height of several hundred kilometres for the ionised layer was the result of a false assumption.
G. W. O. HOWE. Glasgow, March 26th, 1927
[The most careless presumptions were that radio signals were either going up, round a long way and then down - or bouncing from a paper thin shell at one specific fixed height. The ionosphere is far more complex with several regions having different effects and being affected by time of day, season, sun spot cycle, coronal mass ejections... effective height changing slightly all the time. And different effects on different varying radio frequencies. Add a lower region occaisionally absorbing signals before they pass through it to be refracted, sometimes preventing, perhaps only for minutes, any signal passing through to be reflected (shortwave drop out). Short wave reception by "multi hop" is known rather than a signal going up, then round a long way, then down.
For short wave radio "skywave" very long distance communication, the relevant refracting heights are now considered to be based around 110km, 300km and 400km (layers E, F1 and F2)- for a full discussion see
Radio Signal Propagation.(Copy of article on archive.org)]
5GB Daventry Junior
A corner of the control room -
on the extreme left is the separator valve and circuits and next to it, behind a gauze screen, is the master oscillator.
The speech amplifier is shown on the extreme right with the metal front (for screening) removed; next to it is the line corrector in front of which is the volume control.
Further left is the input switchboard and microphone amplifier for local talking. On the left hand bench the master oscillator and separator.
The master oscillator is made to ocillate at very constant frequency; the separator is arranged to take no load from the master oscillator so that whatever happens after the separator valve cannot affect the master oscillator.
General view of the main transmitting room- showing on the right the final stage of the power amplifier; in the centre the six phase rectifier, and on the left the modulated amplifier and sub modulator valves.
On the extreme left is the modulated amplifier (the valve is shown at the bottom of the panel) with its output circuits on the left. The modulator valves and submodulator valve are arranged above the modulated amplifier.
The panel immediately to the right of the door is the first power amplifier using one water cooled valve capable of handling up to 12 kW if necessary. The normal input power is however only 4kW.
The output circuits of this stage are shown on the left of the panel. The tuning control (a car steering wheel) is shown projecting to the front.
The panel on the immediate right of the first power amplifier contains six water cooled rectifying valves of the same type as used at 5XX.
Power is taken from the mains (three phase) stepped up to 10,000 volts by the main trainsformerat the back of the rectifier panel.
The main power amplifier is shown on the extreme right - this consists at present of four water cooled valves each capable of dissipating 8 kW at the anode. The total normal maximum input is 12 kW per valve at an efficiency of 33%.
The two sector type meters in front of the main closed circuit inductance (on the left of the main power amplifier) are for measuring the high-frequency voltages at the grids and anodes of the main power valves to ensure correct working conditions.
The object of these tests was to determine, by means of measurements and reports from trained observers and ordinary listeners situated in all parts of the United States, just exactly what the effect of this enormous increase in power would be. During the week commencing August 14th comparison tests were made between the new 100 kW transmitter and the 50 kW transmitter, which latter is now run at 30 kW., in accordance with the ruling of the Federal Radio Commission.
These investigations, which included measurements of signal strength, audibility and modulation, are part of an extensive development programme, as the result of which the General Electric Company's engineers hope to improve the broadcast service.
By courtesy of the General Electric Company we are able to give the following description of the new transmitter, together with the accompanying photographs, and a brief resume of some of the earliest reports of the results of the tests.
The South Schenectady transmitter laboratory covers 54 acres, and facilities are available for suitable aerial and counterpoise systems, and for the power and cooling requirements of a large number of transmitters, or for a single very large transmitter. There are, for example, four steel aerial towers, three 300 ft. high and one 150 ft. high, in addition to a large number of smaller masts. There is also a rectifier capable of supplying 750 kilowatts of direct current power at 15,000 volts.
High-power Valves Save Space
The development of the 100 kW transmitter has been hastened, to some extent, by the
production by the General Electric Company of a 100 kW transmitting valve.
The new transmitter occupies less than half the space taken up by the 50 kW. transmitter, heretofore one of the highest powered broadcast transmitters in existence. Two 100 kW. valves are used in the high power amplifier unit, and three more in the modulator unit. The 50 kW. transmitter (now operated at 30 kW. as already mentioned) uses seven 20 kW. valves in the amplifier and twelve valves of the same size in the modulator.
The new 100kW valves are of conventional metal anode construction. The anode itself is of copper, approximately three feet long by 3.25 inches in diameter. The grid and filament leads are brought out through a glass cylinder at the top, the glass part being approximately 19 inches long by five inches in diameter. The overall length of the valve is 50 inches, and the filament requires 210 amps at 33 volts. During normal operation two such valves are used in parallel in the power amplifier, which is connected to a closed, or "tank" circuit, which is inductively coupled to the aerial by means of coupling coils and a high frequency transmission line.
The aerial is of the vertical type, consisting of a cage 2 feet in diameter and 240 feet high. The wires of the cage are combined to form a single conductor for the lower part of the aerial, and a counterpoise, consisting of a radial wire system 240 feet in diameter, is used instead of a direct earth connection.
Crystal Control:
The frequency of the transmitter is controlled by a quartz crystal, a method which is rapidly becoming standard practice with American broadcasting stations of the highest class. The output of the crystal-controlled oscillator is amplified by five stages of radio-frequency amplification to a power which is sufficient to energise completely the grids of the two 100kW power valves. All these stages of amplification are completely neutralised, so that there is little possibility of independent oscillation occurring in the amplifier chain. The last stage employs a 20kW water-cooled valve, the output of which goes to the power amplifier.
The frequency of the transmitter is the same as that used by the ordinary WGY transmitter, 790 kC.
Speech or music to be broadcast is sent from the WGY studio over the telephone cable, at a level approximately equal to that used for ordinary telephone conversation. This input to the station is then amplified 1,000 times by an ordinary L.F. (low frequency) speech amplifier, the last stage of which also employs a 20kW water-cooled valve. The output of this intermediate LF power amplifier is then impressed upon the grids of the three 100 kW valves comprising the modulator. These three valves operate directly in the plate circuit of the radio-frequency power amplifier valves, and vary the plate potential in accordance with the speech frequency.
POWER RECTIFIER:
The high-tension power for the plates of these enormous valves is obtained from a rectifier which employs six two-electrode valves.
These valves are the same size as the 100 kW three-electrode valves, only they have no grid structure. The rectifier is capable of supplying 750 kW of direct current power at
a potential of 15,000 volts. Several large filter units smooth out the 60 cycle AC ripple before the output of the rectifier is applied to the plates of the transmitting valves.
A motor-operated voltage regulator enables the operator to vary the output voltage at will, under load. This rectifier is probably the largest of its type in use by a broadcasting station. It is capable of supplying a broadcast transmitter having an output of 250 kW. Although a transmitter of such power is not available at present, it is now considered as being practical.
Cooling Arrangements
In order properly to cool the anodes of the large power valves, it is necessary to circulate twelve gallons of water per minute through the water jacket in which each valve is
mounted. Thus, for the transmitter proper, exclusive of the rectifier, a flow of sixty gallons of water per minute is required.
This is obtained from a centrifugal pump which draws its supply from a cistern of approximately 20,000 gallons capacity. On its return from the valves this water is caused to flow through a radiator unit, which is kept cool by a current of air supplied by a large blower. The water is then returned to the cistern.
This type of cooling system is called a "closed system", since it is not necessary for the water to come into actual direct contact with the air in order to be cooled. In this way the water is protected from dust and other impurities which might adhere to the plates of the valves. Water cooled in this way can be used over and over again for long periods without replenishment.
Simple Remote Control
The operation of this new high-power transmitter is rendered quite simple through the use of remotely controlled electrical relays and automatic protective devices.
The operator has before him two major controls. One switch controls a small rectifier feeding the plate circuit of the (comparatively) low-power valve which supplies the grid
excitation for the main power amplifier; while a second switch controls the high-power rectifier which supplies the plate circuit of the main amplifier and modulator power valves.
In getting the set ready to go on the air as the Americans put it, all motor generator equipment (including pumps and blowers) is started, and rectifiers and amplifiers, both speech and radio, are switched on. When all is ready, the carrier wave is finally switched on to the aerial by the manipulation by the operator of the two major control switches mentioned above.
Protective devices are employed automatically to trip off the power supply in case of valve failure, also to give warning to the operator in case of failure of the water supply. During the transmission of a programme, the operator is continually checking the degree of modulation by means of an oscillograph, and the quality of the transmission is also still further checked by means of a suitable monitoring loud-speaker.
Results of Tests
At the time of writing it is too early to give full details as to the results of the thirty day test of this new high power transmitter, but a sufficient number of reports have already been sent to the General Electric Company to enable them to come to some conclusions.
It must be remembered, when reading what follows, however, that all the tests were conducted between midnight and 1 am at a time when the majority of the Eastern broadcasting stations are closed down, and conditions for long distance reception are almost at their best.
Especially interesting to the engineers engaged upon the tests is the fact that the temporary increase in power has brought an improvement in quality, volume and sharpness of tuning. A survey of the letters received at the conclusion of the third early morning test indicates that:-
Signal strength over the region East of the Mississippi River and North of North Carolina (ie within a range of 500 to 600 miles) is equal to that of ordinary broadcasting stations working within fifty miles of the receiver.
WGY was heard with good volume and clarity in parts of the country not reached since early in the Spring, the volume being so great, in some cases, as to override static and even severe electrical storms.
Fading is not appreciably improved by high power in areas within 300 miles of Schenectady, where WGY's transmissions normally faded; but many of the more distant listeners reported that fading was less frequent and less pronounced.
Many listeners in areas outside the large population zones reported that the 100 kW transmissions were the first static clear music they had received for months.
Static Overridden
It so happened that the first test transmission was conducted under the most severe conditions to which radio broadcast transmission could be subjected, for the greater part of the area reached was covered by electrical storms.
One listener living in Portsmouth, Va (about 300 miles from WGY) reported that lightning was so severe that the street lights in parts of the town were out of commission, yet the storm had no effect upon the music, which came in free from atmospherics.
Another listener about 600 miles away, in Minnesota, reported that WGY's volume exceeded that of his local station, eighty miles away; while Mr. C. C. Hollenback, chairman of the radio committee of station WAIU, Columbus, Ohio (about 500 miles distant) wrote: I wish to advise you that the power overrode the static in a very pleasing manner, and I also want to say that your station had a signal strength equivalent to the strength of our own station WAIU, which uses 5,000 watts, and is fifteen miles distant from my farm home.
A listener fifteen miles from KDKA reported that he got more volume on less (receiver) power from WGY than he did from KDKA (25 kW).
A prominent engineer of the radio division of the U.S. Department of Commerce summarised a technical report on reception as follows: It is my opinion that the efficiency of your station, so far as the delivery of reliable signals to broadcast listeners is concerned, has been increased 100 per cent. This not only holds for coverage but for quality as well.
But one correspondent pronounced the test a failure. He is a resident of Newburyport, Mass, about 125 miles from WGY. He found that WGY faded badly on high power. There never was a high powered station but what was a failure, he stated. You cannot expect a balloon to keep from bursting when you give it too much gas. What becomes of a wave if blown apart.
These preliminary results are of particular interest to British listeners at present, in view of the discussion anent the proposed regional scheme.
When all reports, technical and otherwise, have come in and been duly tabulated and collated, the engineers technical report on the experiments should prove highly interesting. Although no tests have so far been made in daytime, the night-time tests should yield valuable data on the relationship between fading and high power at varying distances.
In conclusion, it might be added that WGY's situation, some distance inland, and in a valley, does not seem to favour the radiation eastwards of his 790kC wave. The station is not easy to receive even in New York city. If, therefore, any readers in this country happened to hear the new transmitter testing, their reports will no doubt be welcomed by the engineer in charge of the station.
[Update from site owner- we now realise that fading can be due to variations in the reflecting layer of the atmosphere caused by variations in solar etc radiation, which are subject to varying cycles. Medium Wave radio travels better over longer distances where the signal passes over a route in nighttime, which in the Northern hemisphere is larger in Winter. Yours truly heard a Boston Mass radio station on Medium Wave one Winter night, in Cheshire. This was before European stations cranked up the power and transmitted 24 hours a day... Short Wave broadcasts generally travel further, more reliably, up to a cut off frequency which varies with solar radiation, and rarely exceeds 32MHz.].
Daventry was the site chosen for the Empire Service short wave transmitters, which operated as Sender 1 and 2 from Daventry from 1932. From 1935 the transmitter used for 5SW was moved from Chelmsford to Daventry where it became Sender 3. Here is a contemporary (1927) article on 5SW:
The experimental transmitter is erected in the research laboratories which have many historical associations, as it was under this same roof that the first long-wave broadcast transmitter was installed and tested before the Daventry site was chosen. Here also 5GB had its genesis.
The present occupier of this historical room transmits on a wavelength of 24 meters, and has the appropriate call sign of 5SW. Power is obtained from a three phase A.C. supply, which is generated on the premises, rectified and smoothed, after which it is passed to the main amplifier at a pressure of 8,000 volts.
The equipment is an interesting mixture of standard apparatus and experimental gear, but everything is laid out with a view to efficiency.
The experimental transmitter consists of two panels of a Marconi beam transmitter, with the addition of three modulating panels, and, of course, the necessary rectifying valves for the various anode supplies. The main amplifier is fitted with two special oil-cooled valves.
The second beam transmitter panel is fitted with two amplifying valves in the top section, and below this the drive or master oscillator totally enclosed in a copper screening box. Each power amplifier consists of two 10 kilowatt valves. It is necessary accurately to balance the supply to both valves, so that meters are included in the filament and anode circuits of each valve to facilitate this adjustment. These instruments and the various tuning controls are mounted on insulating panels on the front of each unit of the beam transmitter. The three modulating panels are mounted in a temporary wooden framework, connected to the oscillators by a speech transforme.
The modulating panels are each fitted with two 7.5 killowatt cooled anode valves, these being connected in parallel and forming the main modulator. This is preceded by a smaller panel carrying two air cooled valves forming the sub-modulator, the function of which is to amplify the signal current received from the land line, or local microphone circuit, before passing them to the main modulator.
The Aerial System
The output from the main amplifier is fed to the aerial by means of a current feeder encased
in a copper tube connected to earth. The purpose of this is to prevent interference from
external sources. At the transmitter end the feeder terminates in a coupling coil and
balancing circuits, and the far end is connected to the base of the aerial. Ammeters are
arranged at either end of the feeder, and the circuits are adjusted so that the current is
the same value at both the input and output ends of the feeder. Slight variation in the
wavelength of the aerial will have no effect on the closed oscillatory circuit, as the
feeder can be considered a resistance.
The radiating system used is a Franklin aerial, and this incorporates a number of unique features based on the experience gained from experiments with beam transmitters.
The Chelmsford aerial takes the form of five half wave aerials, in series with non-radiating portions, connected between each radiating section. The whole system is suspended from a wire, but insulated therefrom, attached to the tops of two 450 foot ( 137 meters ) masts.
It is claimed that by the use of this arrangement every foot of vertical wire radiates energy, and the radiation resistance of the system is of a very high order.
This completes the main equipment, and the writer was then conducted to a small hut which was used as the studio during the recent 36 hour test undertaken with a view to ascertaining what degree of reliability could be expected from a short wave broadcast service.
This room contained a miniature switchboard with direct lines to the local telephone exchange, a Reisz microphone and amplifier and a special amplifier for use with a gramophone pick up device; this provided the matter for broadcasting during the tests.
Reports have been received from many parts of the world, but it seems that the most consistent reception was experienced in Canada, although on those occasions when the Antipodes received 5SW the results left nothing to be desired. Good reception has also been reported by short wave enthusiasts in all parts of Great Britain.
In colonial broadcasting Holland has always led the way, a short wave service to the Indies having been in operation at Eindhoven seven years ago. This description of the newly designed Philips short-wave station at Huizen shows that the early tradition is being more than maintained
SEVEN years ago a dramatic wire flashed into the office of the Philips Radio Laboratory in Eindhoven. It consisted of these four words "We can hear you." This laconic message spelt the triumphant conclusion ot years of patient experiment. It came from Bandoeng, in the East Indies, and signified that the experimental transmitter PCJJ had established communication by short-wave telephony between Holland and her Colonial Empire.
By this achievement Station PCJJ was placed on the road to success; and from the most modest beginnings the experimental transmitter developed into a noted radio station with a large listening public scattered all over the world. The little station received its due acknowledgment and reward when, on July 1st, 1927, the Queen of Holland visited the studio and spoke to her subjects through the PCJJ microphone, addressing a vast unseen audience divided between two hemispheres; one in the East Indies, where Holland has rich colonial possessions, the other in the West Indies, where there have been Dutch settlements since the 17th century.
A Permanent Station
The enthusiasm of the Dutch people at home as well as overseas was unbounded at the success of the broadcast. The question of a permanently established radio centre for the colonies was mooted. The PHOHI station came into being.
The stations strange name is formed from the lirst two letters of "Philips" plus the initial letters of the words "Ornreop Holland-Indie," Holland-Indies Broadcasting. It is pronounced as a word: "fo-hee."
The experience obtained with the PCJJ transmitter was found most useful when the new transmitting installation was being designed and constructed.
Agrarian interests, shipping and oil companies, banks and commercial enterprises were quick to see the importance of the new transmissions to their employees; and they gave full support to the initiation and development of the project.
In the autumn of' 1929 the first experimental broadcasts took place; they were transmitted on a wavelength of 16.88 metres; and with a power of 20 kilowatts, an expenditure of electrical energy regarded as considerable for an ultra short-wave transmitter even to-day. Results were good right from the beginning. A few months after the opening of the new station various American radio corporations relayed a PHOHI Christmas programme; and hundreds of letters of appreciation from American listeners reached Hilversum by the first mail-boat. Reception in the East Indies (the programme including a running commentary on a football match) was particularly good.
The home programmes did much to add variety and interest to the exile of many of the Dutch colonists in the Far East. "No other short-wave station," commented the East Indian journal of Commerce, the Soembayan Handelsblad, "can compete with PHOHI, either with regard to the technique of transmission or the choice of programmes." Indeed, the musical and artistic standing of the new station reached ahigh standard of excellence.
In spite of the efficiency of this particular station, broadcasting in general in Holland at this date had become erratic and chaotic. Active Government intervention was decided upon, and the innocent had to suffer with the guilty. The colonial station was closed down, and remained silent for two years. At length, after protracted negotiations and in response to urgent demands from the Indies, a compromise was effected, and the reopening of the station was arranged for the autumn of 1932.
The official inauguration took place in December of that year. But the general enthusiasm was somewhat tempered when it became apparent that reception in the East was not up to the standard attained during the experimental period.
No efforts were spared to overcome the obstacles of the ether, and various experiments were attempted; the times of the broadcasts were changed but with little result ; then a second wavelength for winter operation was granted to the station. In January, 1933, broadcasting was discontinued while the station was reconstructed to allow for transmissions on the second wavelength. The experimental work began again in March, but this time not only with the ordinary wavelength of 16.88 metres, but also with the new winter wavelength of 25.57 metres. Results were exceedingly satisfactory, so that on April 16th, 1934. PHOHI officially resumed broadcasting, and once again its call letters PHI echoed round the world.
But the experts of PHOHI still pursue their quest after technical perfection. In a vast geographical entity such as the Indies it is inevitable that there should be complaints of imperfect reception from certain districts. In Northern Sumatra, for instance, listeners-in suffered from serious interference from a telegraphic transmitter. This was overcome by experimenting with two simultaneous transmissions on different wavelengths, PHI using 16.88 metres and PCJ using 19.71 metres.
The colonial broadcasting station and aerials are situated near the village of Huizen, on the Zuyder Zee, some 15 miles south-east of Amsterdam. The current supply is 10,000 volts 50 cycles.
The high-frequency part of the installation is in the middle, and the transmitter is crystal controlled. By the application in this stage of an ordinary receiving valve (A 415) the crystal is only slightly loaded, which greatly strengthens the regular functioning of the transmitter. The frequency of the vibrations generated in the crystal stage are in the following stage multiplied several times in order to obtain the right wavelength. For instance, on the 16.88 metres wavelength the crystal stage is tuned on 135 metres. Before the frequency of the 67.5 metres wavelength is doubled, the vibrations are amplified by two parallel and connected 10-watt valves. The doubling takes place afterwards up to 33.75 metres, the highest voltage used in these stages being 400 V. But the following amplifying valves work under an anode tension of 2,000 V. The final doubling takes place in two 1,500-watt valves up to 16.88 m. When the high-frequency energy has once more been amplified by two parallel-connected 1,500-watt valves, fed by 4,000 V. DC, it comes into the last amplifier stages, consisting of two 10kW. water-cooled valves. The tension for this stage is 10,000 volts, and there is a current of 6 amp. intensity.
The power of the transmitter is thus 60 kW. and its output 20 kW. at 97 per cent modulation.
The modulation apparatus is in another part of the building. The HT is obtained from two rectifiers supplying respectively 8,000 volts (3-phase rectification) and 14,000 volts (6 phase rectification). The total input reaches 130 kW.
Advantages of the Beam
The control desk is in a central position, and the operator from his glass-enclosed perch can survey the whole installation. In case of emergency the whole transmitter can be put out of action by one movement of the hand.
The aerial system is of the beam type; in other words, it radiates in two directions only, east and west. This method ensures much better reception, both for the East and West Indies, than would be possible if a non-beam system were employed.
The principal studios of PHOHI are in Hilversum, whence most of the programmes are broadcast. There is also a special studio in Amsterdam for broadcast talks, and a studio in the Hague used for the concerts given by the Residentie Orchestra, which is the pride of the capital. For special occasions a music studio is fitted up in the actual transmitting station at Huizen.
The Programmes
Besides the Residentie Orchestra PHOHI has at its disposal an excellent orchestra of its own. Classical and modern compositions, light music and jazz, cabaret, running commentaries on foot ball matches, general outdoor broadcasts - all have their place in the regular programmes.
Many events of national importance have to be recorded and rebroadcast from gramophone records at a more convenient hour, for the difference in time between Europe and the East Indies is about six hours; when it is 9 p.m. on Wednesday in Huizen it is 3 o'clock on Thursday morning in Batavia.
PHOHI specially prides itself on its news service; its bulletins are read by Mr. Edward Starz, who is able to address his vast cosmopolitan audience is no fewer than seven different languages.
The station's popular announcer is now making a tour of the East Indies to meet face to face some of the many thousands who know only his voice.
On the cultural side the station's aim has always been to bridge the gulf between Holland and her colonies, to form an enduring spiritual link between the Netherlands and the Dutch Colonial Empire, east and west.
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