[Boatanchors] Receiver Technology
gzook at yahoo.com
Mon Jan 17 19:47:01 EST 2011
Actually, Marconi's patents were vacated over about a 20 year period with his very last patent being vacated to Tesla in 1943. The Dolbear patent, U.S. Patent #350,299, issued in 1885, kept the Marconi Company from operating in the United States until Marconi bought the rights. Dolbear's patent was for a system that was virtually identical with Marconi's.
The coherer was invented independently in the United States by Dolbear and in the United Kingdom by Oliver Lodge, who tried to use it to receive emissions from the Sun. Of course, the sensitivity was no where near what is required to receive sun noise. Marconi used his Irish grandfather's influence to promote his wireless company in the U.K. A number of very influential persons, including Members of Parliament, invested heavily in the Marconi Company and the British government did everything possible to eliminate patent challenges to Marconi to protect their investments.
Basically, Marconi invented nothing. As such, he is not entitled to fame as the "inventor of radio" for which he received the Nobel Prize. However, through his company, Marconi definitely did considerably more than anyone else to promote the usage of wireless and for that he certainly is to be recognized.
Fessenden was broadcasting music and voice by means other than a modulated spark in the very early 1900s. However, his system was only useful for ranges of just a few miles.
--- On Fri, 1/14/11, Bill Hawkins <bill at iaxs.net> wrote:
It's a quiet, snowy afternoon in Minneapolis, so here are some thoughts on the history of radio.
"Syntony and Spark" by Hugh Aitken is a fine coverage of early radio up to the allocation of "200 meters and down" to radio amateurs in the 1920's.
Hertz and Maxwell had discovered and created the science of radio waves 40 years before. Nobody said, "Hey, let's build a radio broadcasting system and make our fortune by selling advertising."
The economic driver seems to be the need for telegraphy at sea. Businesses could track the flow of money with the land telegraph, but ships at sea were lost until they showed up in port.
There was money to be made by being the first to trade for the ship's cargo.
Marconi became the "Father of Radio" by developing long distance wireless telegraphy using powerful spark transmitters and coherer receivers that could be used aboard ships. Others could claim the "Father" title, but Marconi was the first to make enough money at it to become noticed - and he had the patents, until we awarded them to Tesla in 1943.
This was fine if you had the only such wireless circuit and the only noise came from nature, but that condition rapidly deteriorated as more and bigger spark transmitters were developed to meet the needs of business. SOS was just a nice side effect.
Efforts to use resonant circuits (syntony) helped for a while, but the field kept growing. DeForest's imperfectly understood Audion triode made it possible to build more sensitive receivers.
And there it stood until someone understood the need for voice, in the manner of a wireless telephone, who also had the knowledge and creativity to modulate the transmitter.
After that, people began saying, "Hey, let's build a radio broadcasting system and make our fortune by selling advertising." And so, radio systems evolved as inventors seeking fame and/or fortune began tweaking the existing methods.
At first, a carbon microphone was used to modulate a spark transmitter by shunting the antenna power. The mic got very hot, but DeForest receivers could hear a voice. Some mic's were water-cooled. This let the announcer get closer to the mic.
Marconi said in 1928 that he'd made a mistake by assuming that long distance required long waves and high power to punch them through the QRM. Modulated vacuum tube oscillators and TRF receivers made radio broadcasting possible when power requirements dropped with the use of short waves.
The use of money to drive progress, and a history of trial and error is typical of all projects. The power of science to predict answers saves a lot failed trials. But if there's no money in it, why bother?
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