Keith Wilson - Electrical engineer
We all think we know who invented radio – it was Marconi, of course! But actually it wasn’t. Marconi was certainly a very successful pioneer in the field of wireless telegraphy—although many of his claims as an inventor are open to challenge—but telegraphy is all about transmitting the dots and dashes of Morse code, not the speech and music we associate with radio today. In reality, the foremost pioneer in the field of wireless telephony was, without doubt, Edwin H Armstrong.
Though his name is largely forgotten, Armstrong’s contributions to radio live on in the radios, televisions and even many of the mobile phones we use today. In contrast, you will struggle to find any direct legacy of Marconi’s work in these present-day devices.
But what did Armstrong invent? Let’s start with the valve (vacuum tube if you’re American) oscillator. Before Armstrong invented this in 1913, while he was still an undergraduate at Columbia University, if you wanted to generate the continuous radio waves essential for the transmission of speech and music, you used a high-frequency alternator. This is a machine much like the alternators used today to generate power, except that instead of operating at 50 or 60 Hz, it operates at frequencies nearer 100 kHz.
The valve/vacuum tube oscillator was an enormous advance that made it possible to build—at reasonable cost—radio transmitters in every town and city. In short, Armstrong’s oscillator made broadcasting not just possible but feasible and commercially attractive.
If he had invented nothing more, his oscillator would have been a remarkable achievement, but his next innovation was the superheterodyne radio receiver. Before this, radio receivers amplified the signal from the transmitter at whatever frequency it was transmitted. That meant if you wanted to listen to different stations, each operating on its own frequency, your receiver had to be able to amplify efficiently at all of these frequencies.
Armstrong’s brilliant insight, in around 1918, was to realise that it would be much better to convert all of the incoming signals to the same frequency before amplifying them. He did this by heterodyning (beating) the incoming signal with a signal from a variable frequency oscillator within the radio receiver. Since the heterodyning used frequencies above the audible range, this became know as the supersonic heterodyne principle, which was very soon abbreviated to superheterodyne or simply superhet.
With this arrangement, the radio only had to amplify efficiently at one frequency and was, therefore, much easier to design and build. In fact, the superheterodyne principle works so well, that is still used in almost all of today’s radios and televisions, as well as some mobile (cell) phones.
But even two revolutionary inventions were not enough for Armstrong. His next innovation was FM radio. Until around 1940, all radio broadcasts used AM or amplitude modulation, where the amplitude of the radio frequency carrier wave is modulated by the speech or music being transmitted. Armstrong proposed, however, that it would be better to modulate the frequency of the carrier (frequency modulation or FM) rather than its amplitude, not least because FM signals could be received free of the interference that plagues AM reception.
For the sake of accuracy, it’s only fair to mention that this time Armstrong’s role was not that of inventor. FM had been considered by others but had been dismissed as impractical. Armstrong’s contribution was to ignore the naysayers and develop FM so that it became a practical and attractive proposition.
Once again, he was right and it’s a fair bet that if you were listening to the radio as you drove to work this morning, you were tuned to an FM station. But being right doesn’t always lead to a good outcome, and so it was for Armstrong. In the late 1930s FM radio, which Armstrong convincingly demonstrated at an IRE conference in 1935, was the last thing that the powerful Radio Corporation of America (RCA) wanted.
RCA had invested heavily in AM broadcasting across the USA, and was looking forward to making a lot of money out of the coming of television. It really did not want to see its AM broadcast network made obsolete by the coming of FM. To cut a long and very sad story short, the hostility of RCA toward FM led to long and costly legal wrangles that drained Armstrong of the fortune he had made from his earlier inventions.
Armstrong and his new wife Esther Marion MacInnis in Palm Beach in 1923. The radio is a portable superheterodyne that Armstrong built as a present for her.
Stressed, saddened and disillusioned, and with his health deteriorating, he committed suicide on 31 January 1954 by jumping out of a tenth storey window. But that’s not quite the end of the story. Just before he died, Armstrong had filed 21 lawsuits against infringements of his patents. After his death, his wife pursued these, won two of them and settled all of the others successfully. Vindication of sorts, but in truth too little, too late.
We would like to thank the IET Archive for providing much of the material on which this article is based.