Re: Doubling

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
.

Relevant Pages

  • The doubly tuned circuit-key to clean hetrodyne or premix transmitters
    ... frequency like 8MHZ or less with the signal from a crystal oscillator ... The mixer MUST be fed at least 10 db more high than low ... out-almost always with one or more harmonics too close to the carrier ... or couple a FET to the top of the secondary coil. ...
    (rec.radio.amateur.homebrew)
  • Re: Doubling
    ... In terms of old transmitters from the 20s/30s...In a crystal oscillator ... I understand the concept of setting the oscillator output tank to ... Some oscillators make the crystal operate on an overtone. ... Overtones close to odd harmonics are usually much more active in the ...
    (rec.radio.amateur.homebrew)
  • Re: Twin T Notch Filter Anomaly
    ... source resistance oscillator I was getting different distortion readings ... with and without the notch and at first I thought I had the calibration ... 50dB I should be able to read harmonics down to -120dB. ...
    (sci.electronics.design)
  • Re: Doubling
    ... In terms of old transmitters from the 20s/30s...In a crystal oscillator ... The non-linearity of the stage will produce the harmonics, ... (and filtering stage) ... overtone oscillator tuned at 30 MHz will not produce exactly 30.000... ...
    (rec.radio.amateur.homebrew)
  • Re: Doubling
    ... In terms of old transmitters from the 20s/30s...In a crystal oscillator ... I understand the concept of setting the oscillator output tank to ... If the energy extracted from the oscillator is at twice the crystal frequency it's because of harmonics generated in the tube. ... One description I read of the tritet osc described it as being an oscillator with inherent class c amplification, hence the plate circuit being tuned to the desired 'harmonic' and the crystal is indeed operating at its fundamental freq. ...
    (rec.radio.amateur.homebrew)
Loading