Friday, September 15, 2006

CW vs AM, Vinyl vs CD

Radio is a little over a hundred years old, and there was a period from about 1900 to about 1928 when radio was an experimental medium that hadn't reached the masses. But commercial communications and telegraph companies were making a lot of money sending messages across the Atlantic and elsewhere, and all of that communication was in the form of code: Morse Code, American Code, and other codes comprised of short and long dots and dashes. Originally generated by sparks, the on-off dots and dashes had a lot of noisy bandwidth and interfered with each other too.

It wasn't until the oscillator was invented that true "CW" or Continuous Wave transmissions - smooth notes of on and off - could be transmitted. These signals took up a lot less bandwidth and concentrated more power into a particular wavelength, or frequency. Whole industries grew up on the use of dots and dashes, helped along by a trained pool of telegraphers who already had been tapping out messages over Western Union wires strung along all the rail systems.

But the ordinary person couldn't much appreciate all those dots and dashes which sounded like gibberish and still do. It wasn't until the invention of the microphone that an audio signal could be superimposed over a steady, continuous wave, using a process still known today as modulation. The early modulators were carbon microphones placed in series with part of the oscillator. Since the oscillator had high voltage on it, you needed to keep away from the mic, or get your lips burned. There were a lot of shocks and "RF burns" in those early days.

The first modulation system was termed "Amplitude Modulation" or AM, as it varied the amplitude or strength of the signal according to the speech or music signal applied to the transmitter. This system is still in use, and some people believe it has a certain pleasant sound unlike that of FM or digital.

When AM first arrived, the old CW telegraph ops didn't like it. They were used to the dots and dashes which were music to their ears, so they fought it. When FM arrived, all of the static and noise common to AM broadcasting was gone, but certain people still thought that AM was more natural sounding than FM. It's easy to see the analogies to the tape vs protools arguments, and even the persistent vinyl vs CD dissonance. We know that innovation traditionally requires the disposal of some portion of the old that is cherished by those who have mastered it.

This year we celebrate the 100th anniversary of AM, apparently first used by Reginal Fessenden right here in nearby Marshfield Massachusetts, nex to the ocean. Fessenden's station "BO" (Bravo Ocean) was already in operation sending messages across the Atlantic in code, then he adapted the transmitter to do AM, and broadcasting began.

Here is a site dedicated to Fessenden's work, with a cool picture of his tower - a big one - at Brant Rock in Marshfield.
The tower is long gone.

Above you can see a more modern telegraph key that is still used today to do the primitive on-off keying to send signals across the ether. Why do people still do it? Why go sailing when you can hit the gas on your power boat? There's something about the economy and simplicity of "CW" to those who know the "code". In the middle is a crystal microphone from an old tape recorder I got on Christmas when I was a kid. Click on the image to get a good close up view.

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