On Fri, 21 Nov 2008 22:30:24 -0400, exray wrote:

This is a really dumb question but it dawned on me that I did not know
the correct answer.

In terms of old transmitters from the 20s/30s...In a crystal oscillator
I understand the concept of setting the oscillator output tank to
favor the harmonic from the crystal. (Stop me if I'm wrong already...)

You're wrong already, kinda.

Most of the schematics that I've seen from back then have the crystal
oscillating at it's fundamental. If the energy extracted from the
oscillator is at twice the crystal frequency it's because of harmonics
generated in the tube.

I don't have a lot of reference material to look at, but I don't think
that using a crystal's overtones to generate RF really picked up until
the 50's (it was probably done during WW-II, but I only see it put forth
as a common method starting with my '50's ARRL handbooks).

But in a doubling amplifier stage am I counting on having enough
harmonic content at the input or am I creating the harmonic with the
non-linearity of the amplifier?

You're creating the harmonic with the nonlinearity of the amplifier. A
class C stage (which is pretty much assumed for CW transmitters) is very
rich in harmonics, and the harder you drive it the higher the harmonics
go. So it's pretty easy to get one to generate considerable energy at a
harmonic frequency, which you then pick out with your tank circuit.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html