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Old July 29th 05, 01:52 AM
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John, I'm very serious when I say that 'white noise' is critical to
Colpitts/Hartley oscillator operation.

The feedback equation for oscillation requires a voltagecurrent gain
greater than 1 and a phase shift of 180 degrees [in simplified terms].

Starting conditions, in the absence of white noise, has zero input
voltage and hence zero output voltage and therefore no oscillation! The
presence of white noise provides the starting conditions, the Vin to be
amplified, and the tuned circuit, L and C, provides the frequency
discrimination, and the fundamental frequency of the oscillator. The
Capacitive voltage divider [Colpitts] or the Inductive voltage divider
[Hartley] provides the feedback factor. The active device, tube,
transistor, FET, etc. provides the gain and contributes to the phase shift.

White noise, frequency selectivity, gain greater than 1, and 180 degrees
phase shift are absolute requirements for an oscillator. In the absence
of any one there is NO oscillator. The white noise provides the starting
conditions for oscillation!!!

John Smith wrote:
Hmmm...

No, I don't believe I will have to read anything...

But, if you can't tell the difference between a white noise generator and an
osc giving a clean fundamental signal with greatly suppressed/filtered
harmonics (or even, non-existent harmonics), you may wish to read-up before
taking that project to the air...

John


 
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