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I'll finish off my excursion in to this pre-electronic radio era with a last receiver.
This one, to me anyway, represents the highest point in the electrical-mechanical art of radio . I say it like that, because at the turn of the 20th centuy, all things radio were just variations of mechanical contraptions- steam driven electric generators driving bizarre sparking-arcing monsters, huge antenna and long wavelegths that were barely understood, receivers that centre'd around metallic slivers of silver-- all machines- nothing that could be truly called electronics today.
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That is why these are SO like out of Jules Verne. And for us, as fantastic as his Steam Punkish world of the future is to us now; the more I understand the technology of that era, the more I marvel at how well it all work'd. Like I said somewhere earlier, its like communicating over vacuum cleaners.
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My last, and final entry into this museum fin de siecle of vacuum cleaner radios is the Marconi Magnetic Receiver- Affectionately known as "Maggie." Fans of all things RMS Titanic may remember that the S.S Californian had a Maggie. Even though its regular radio officer had gone off duty (after being blasted by the Titanic to "Shut up !") another operator, idly tried to listen on the receiver. Maggies are mechanical devices run on a clock work-- and it wasn't wound up -he didn't realize it-- the Titanic's "CQD" was never heard.
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I was going to describe the theory behind one of these magnetic receivers... its quite interesting if we want to get into magnetic hysteresis, iron filing noises and such. But it gets involved, and right now the task seems daunting (I'm in a place best described by another Victorian as 'where the climate is bad and the water makes men sick")-
A Maggie uses a continuous loop of iron Litz wire, that runs in a loop thru two magnets. There is a coupling coil that induces a magnetic flux into the wire in the presence of an RF field. By this induction, there are hysteritic changes in the wire that can be picked up by a telephonic device- the signal heard is the actual radio signal- not some click heard on a coherer receiver.
I said it got involved. No?....
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The Maggies were used on ships since they were far more sensitive than coherer receivers, and quite immune to being bumped about in bad weather. They remained popular up until the mid 'nineteens- when with the coming of the Fleming and De Forest valves (tubes) they faded away as dinosaurs.
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I have one that I like to use in demonstrations. It works quite well, and the sounds out of the telephone ear piece are very much like listening to a crystal set-- except that loop of iron wire is very noisy- old time operators had to endure a loud, wind-like sound listening on them. Another interesting Noise Figure quite unknown today-
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Okay, my lecture series is complete - smiles. I hope some of these early-code mechanical freaks and beasts may spark further interests in radio's history.
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Lauri .............................. SK'ing
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