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Radio Pioneer

My grandfather's principal interest, outside work, was radio experimentation and research.  

In the 1890's experiments based on James Clerk Maxwell's theory of electromagnetic radiation by Hertz, Tesla, Marconi and others demonstrated the practical transmission of radio waves but without a suitable amplifier they were limited to sending Morse code, using spark gaps to generate the necessary high frequencies.

Scientists at Edison's laboratory had identified thermionic emission, which became known as the Edison effect, but only as a nuisance that they thought was due to carbon atoms boiling off the heated element. 

Despite other advances in radio they failed to realise that it was actually electrons being emitted and hence to see it's potential (same pun - intended).

The English physicist John Ambrose Fleming realised that the thermionic emission was electrons - and could Thus,
provide a one way 'valve' directing the flow of electricity. In 1904 he patented the first vacuum-tube rectifier or thermionic valve also known as the Fleming valve.  Within a year a young American, Lee DeForest, realised that by placing 'grid' between the cathode and the anode he could regulate the flow of electric current through the valve by means of a control voltage applied to the grid. 

Thus, DeForest had invented, and in 1906 patented, the first triode: a device capable of electronic signal amplification. In early valve catalogues this quality is still called 'magnification'.

This device is still known as a valve (in England and Australia and so on) and as a vacuum tube or just 'tube' (in the US). 

 


Triode examples, showing the enormous technological development from 1918 (left) to the 1960s
The valves used in walkie-talkies and hearing aids got down to three centimetres long and the diameter of a pencil
Size reduction improved a number of performance characteristics and allowed much more compact chassis
but required much greater manufacturing precision
These were superseded by discrete transistors the size of a pea and then by the microchip and surface-mount devices 
(picture by RJB1 - via Wikimedia Commons)

 

The triode was probably the greatest invention of the early 20th century, surpassing even the contemporary Wright Brothers mastery of powered flight. The triode heralded the electronic age without which modern aircraft could not exist and it powered the first electronic computers that were an essential step to incredible scientific and engineering advances, including decoding our genome. 

Now electronic circuits could switch each other on and off in logic circuits or be made to oscillate indefinitely in a radio transmitter as the valve made up the losses due to power being absorbed by the aerial and its radiated transmission or magnify and transform the tiny electrical signals picked up by an aerial, until they were large and powerful enough to drive the voice coil of a booming loudspeaker.

AT&T purchased the DeForest patent and used it to make the first audio modulated radio broadcasts in the summer of 1913, transmitting realistic voice and music as we know it today, no longer restricted to a sequence of Morse Code dots and dashes.  The year before my grandparents were married modern Radio had been heard for the first time.

Initially Edison's carbon microphone had been inserted into the circuit to 'modulate' the amplitude of the signal, with voice or music, providing the first amplitude (or audio) modulated (AM) broadcasts.   But it was quickly realised that suitably designed valves could be used to amplify the tiny signals from higher quality microphones that could be connected by wire to the transmitting equipment. Not only that but in addition to driving loud speakers they could drive other devices, like the cutter that made the grooves in a record.

As in aircraft technology and many other fields major advances were made in radio valve technology and radio transmission during the First World War.  Soon both planes and radio messages were circling the globe.

Soon after moving in my grandfather created a workshop in the basement their home at Queens Road, Monkseaton, where he experimented with radio designs and transmission.  To facilitate his investigations, after the War was over, he had constructed the largest privately owned radio mast in the North of England, in their front garden.

Some time after we had settled in Australia my father was interviewing factory workers and one interviewee announced that he knew the name McKie because he had helped to build his father's radio mast.  It was quite famous.

The first public news and entertainment broadcast in Britain took place on November 14th 1922 from a 1.5kW medium wave transmitter broadcasting from the top of Marconi House in London.

So, my grandfather built a 12 valve receiver on which the family and friends could gather-round and listen to 'London Calling', the first entertainment radio and the beginning of the BBC, a considerable novelty.  It was like the beginning of television. 

His set must have been impressively large, as valves were similar in size to incandescent light bulbs.  It would have used a lot of power for that time, and generated a lot of heat, around that of an electric room heater.  All the valves would have been triodes. Multi-grid valves were not yet commercially available. 

I have made a guess at the circuit based on contemporary records and designs my father built and told me about. 

The audio section is probably easiest to guess at because I know he wound his own output transformers and the business he worked in wound commercial motors and dynamos. This suggests a push-pull design requiring five triodes and a purpose-wound output transformer driving the loud speaker. Proper balance is extremely critical to avoid distortion and such transformers weren't an off-the-shelf item back then.  So, it's not surprising that my father in turn often wound his own coils and transformers and I grew up with dozens of rolls of different gauge winding wire in a kitchen cupboard.

I'm assuming that JWL McKie's famous 'big receiver' was a superheterodyne design to improve sensitivity and selectivity.  The idea of intermediate frequency is attributed to Armstrong in 1918.  The concept was in the literature and use by radio enthusiasts as early as 1920.  My grandfather would certainly have experimented with this technology and his son, my father designed and built a wide range of devices using the same concept.  But it was difficult to implement with triodes and was very fussy back then.  It soon became commonplace after the invention of multi-grid and multi-element valves and became the dominant radio and television receiver technology from the 1930' to the present day. 

Early triode superheterodyne designs had a separate local oscillator and mixer.  A typical design would account for a further six valves with three IF stages.  The twelfth valve may have been initial RF amplification.  I'm assuming that he was using a DC mains supply directly for the HT rail and put the heaters in series, for reasons that will be obvious later.

It certainly would have been quite a wireless.

My grandfather instilled a love of research in my father who was encouraged to help in the workshop, to make his own crystal sets to listen to broadcasts and to perform other small experiments, like making his own lead sulphide crystals.

While melting lead one day my father used a soldered can so that the lead ran out through the soldered seam and scarred his foot.  He would show me the scar and tell me to be careful not the make the same mistake when melting lead.  He was around six or seven at the time of the accident. There was no suggestion that I should refrain from melting lead - but avoid the fumes and wash your hands before eating.

My father, in turn, helped me make my first crystal set, showing me how to neatly wind my coil.  The variable tuning condenser came from an old radio and I used my pocket money to buy a pair of earphones, my pride and joy.

Before suggesting the project, he'd raised my interest by giving me a mysterious device that turned out to be a cat's whisker holder, together with a (commercial) crystal of lead sulphide or perhaps one of the other suitable crystals to put into its crystal holder.  It came from 'Radio House', a hobby-shop in Sydney long since gone, and it looked exactly like this image I found on the net, like seeing a picture of an old friend:

 

crystal detector 01
Cat's Whisker crystal-detector
To the right is a housing that holds a suitable metallic crystal like lead sulphide
To the left is a bar with a ball socket that mounts the fine wire or cat's whisker
The whisker is moved over the crystal until a diode detector forms, heralded by hissing in the earphones.
 

I took my crystal set to school in fourth class for 'show and tell' but it refused to work having been shoved into a box for transport.  I was mocked by our teacher who said that if I spent as much time leaning my spelling list as I did on all this nonsense, I would do much better at school.

Interestingly if you put a battery and shunt across the cat's whisker junction it would emit a dull light in the dark, which might have been a little arc.  But we now know to be a light emitting diode or LED.  No one thought much of it at the time and it demonstrates that it takes an enquiring mind to look beyond the obvious.

Years ago, my mother wrote:  Stephen's personal memory of his father is of love and admiration for a man who always had time for him.

Thinking back, I could say the same thing about my father.

In the early 1920's amplification of electronic signals from a passive, but higher quality, microphone, using the new triodes and later, pentodes, brought in the Jazz Age and allowed a new style of singers, the crooners, to sing into the new microphones.

The same technology enabled the Public Address (PA) system that US President Woodrow Wilson used in 1919 to address a crowd of 75,000 in California.  Numerous innovations in the first years of the 1920's soon resulted in public radio transmission for entertainment, information and propaganda.

By the late 1920's President Wilson's feeble 25 W PA system was surpassed many times over with systems driving up to 200 loudspeaker horns.

Thus, the rise of Hitler and Mussolini was in no small measure due to the invention of the triode valve and then the pentode.  All the result of the evolution of the thermionic valve (vacuum tube) from a humble electric light bulb.

My grandfather did not invent a new type of valve.  Pentodes were not invented until 1926.  But he made pioneering advances in circuit design that my father was proud of and spoke about. 

Numerous other radio stations quickly followed the first amateur transmissions, addressing this audience with local content, including briefly my grandfather's own broadcasts. It was a bit like the 'dot com' explosion, when websites proliferated.

The Geneva Frequency Plan of 1926 put an end to this radio proliferation.  But by1926 my Grandfather no longer cared, he was dead.

 

 


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