[Boatanchors] Receiver Technology

[Bill Hawkins]

Wilson, and all,

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?

And that's enough for now . . .

Bill Hawkins

-----Original Message-----
From: Wilson Lamb
Sent: Friday, January 14, 2011 2:37 PM

I wrote the following message after giving some local talks that reminded me

there were some years not well represented in my view of receiver evolution.

If anyone has insight to any of the questions or uncertainties mentioned, 
please drop me a note with whatever you care to offer.

Thanks, Wilson, W4BOH