Sunday morning we listened to the In Our Time episode about the invention of radio, which we’ve had sitting on the ipod for a while – it’s not a subject that caught either of our imaginations in advance. It did turn out to be interesting, but it also felt like a series of vignettes – this person, this date, this advance, now move on to the next – so I’m approaching writing it up with some trepidation! The three experts on the programme were Simon Schaffer (University of Cambridge), Elizabeth Bruton (University of Leeds) and John Liffen (Science Museum, London).
At the beginning of the show Bragg introduced the subject by talking about Marconi and the patents he filed in the early 20th Century that mean he is often credited as the father of radio. When they discussed him, towards the end of the programme, they talked about how he liked to present himself as coming up with the whole thing himself. He didn’t give many (if any) of the people who’d previously worked in the field credit for their achievements. But as the programme had just demonstrated, radio wasn’t invented in a single flash of genius but was instead the result of an accumulation of nearly a century of small advances.
Before the 19th Century if you wanted to send a complex message a long way, then it could only travel as fast as you could transport a person carrying it. Experiments with electromagnetism in the early 19th Century started to change this, and by the 1830s a system of transmitting messages along a wire had been developed – the telegraph. At first the pioneers of this technology had envisioned something that would twist a needle to point at the required letter of the alphabet, but the work of Morse & others established a technically easier method involving a simple code. The telegraph took off pretty rapidly, but developing a wireless method would take much longer.
James Clerk Maxwell came up with a theory of electromagnetism that predicted electromagnetic waves. At first this was purely in the realm of theory, and proving it experimentally posed a variety of technical problems. You have to design and build apparatus to emit these waves, which was eventually done in the form of a spark-gap transmitter – I don’t think they explained how this worked on the programme. And then having done this you need to reliably detect the resulting waves. They talked about a few of the ways that were developed, but I didn’t really follow any of them and so have forgotten the details :/ Over a period of several years successive scientists and engineers made their own contributions to the field, but the definitive experimental proof came from the work of Hertz in the late 1880s.
This is still science rather than technology – none of the people involved so far in the story were thinking in terms of commercial applications, it was just an interesting phenomenon to investigate and try to explain. The Post Office, in Britain, oversaw the domestic telegraph network and was beginning to be interested in possible applications of wireless technology. However there was some pushback because the telegraph system worked so well, so why develop something new? There was a similar thought process at work in the early days of the telephone system too – the postal system worked so well, why would anyone need a phone?
Even once it was known to be theoretically possible to transmit and receive electromagnetic waves wirelessly there were still several practical obstacles that needed to be overcome. For instance at first transmitters transmitted across a wide range of frequencies – so if there were two transmitters relatively close together then their signals would overlap and a receiver wouldn’t be able to pick out the message from one or the other. So one of the advances that had to be made was in the concept of tuning – restricting the transmitter to a particular subset of frequencies and then only listening to one of these bands. Another obstacle to be overcome was in the sensitivity of detectors. This was done in part by a man called Bose, who was working in Calcutta. The detectors used didn’t operate as well in the humid environment of India, and so Bose had to develop a modification of the design – which was then better in other environments too.
And we’re back to where Marconi enters the story. He was a young man from a wealthy Italian family, and despite his protestations otherwise what he did was to put together all the various prior work on wireless technology and figure out a commercial product. He’s helped in this by the fact that he’s rich, well connected and good at publicity. He also came up with a niche for the technology – ships! Obviously it’s not practical to trail a telegraph wire after a ship that’s sailing across the Atlantic, so this is an application where wireless has obvious answers to the “why bother?” question. Most people at that time (including people like Tesla) thought that electromagnetic waves would move in straight lines, so this is a case where Marconi not really understanding the science worked out in his favour – he just set up trials at doing a transatlantic transmission from Cornwall to the US. This was a success and he was then able to market his devices for use in shipping.
These radios were still transmitting code rather than sound. The programme didn’t spend much time covering the next stage because it was getting towards the end of the time they had available. But basically instead of transmitting bursts of waves, instead this built on the work of Tesla (I think) and transmitted a continuous radio signal. The modulations of this signal were then used to carry information that could be decoded into the original soundwaves recorded by the microphone.
I’m not sure I’ve done the programme justice with this write-up – in particular there were a lot of little biographical snippets for the various figures involved in the story that made them come alive as people, and I haven’t conveyed that at all.