"Anthony Fremont" wrote in message
...
Pictures available in ABSE

The top trace (yellow) is taken between C4 and R2. The bottom trace
(cyan)
is taken at the base of the transistor. There is a switchercad file, but
the simulation will show allot of distortion that really isn't present in
the prototype circuit, because of lots of circuit capactance I suspect.
R1
was something I was playing with to try and tame the voltage across L1/C3
being applied to the base.


Hello all,

I was tinkering with this LC oscillator (Colpitts/Clapp) this weekend. I
arrived at the values of C1 and C2 empirically after starting with a
crystal
oscillator circuit. The values in the original circuit created a horrid
waveform that looked allot like the simulation. After much tinkering
around
and simulating, I come to the conclusion that getting a perfect waveform
is
nearly impossible, especially with big swing. It seems that the
transistor
likes to take a bite out of the right half of the peak of the wave.

What is the secret to beautiful waveforms? Do I need another LC resonator
on the output to fix it up? I mean, I'm getting a pretty nice wave now,
but
there is still some distortion that you can just see at the top of the
peaks
on the yellow trace.

How do you control the peak voltages of an LC resonattor without mangling
the waveform? The waveform at the junction of L1/C3 is of course quite
beautiful, how do I get it from there to the output? ;-)

I realize that I will need a buffer stage(s) before I can make any real
use
of the signal, but I want the input to the buffer to be as perfect as
possible.

Thanks :-)

The prettiest waveforms come from balanced oscillators. Distortion then
turns up as 3rd 5th 7th etc harmonics which are far less ugly than the 2nd
3rd 4th 5th etc generated by the single ended types. Balanced ALC is also
easier and more effective.
My own experience says that 'prettier' is better. Those oscillators offering
gross distorted outputs also seem to suffer badly in other areas and gross
distortion always causes problems further down the line.
Procuring good quality is a classic black art, one aspect is to allow the
LC just an occasional vague glimpse of the maintaining amplifier. Another is
to cause limiting by use of an amp having a gentle gain change (eg Fet v
bipolar) and the other is ALC. (Or all three together).
Failing that, there is always the cop-out of an output filter
john



--
Posted via a free Usenet account from http://www.teranews.com