Am 06.02.2017 um 14:08 schrieb Richard (Rick) Karlquist:
Agreed, for low phase noise FLOOR, it is imperative to
take the signal out through the crystal. However, for
close in noise (say ADEV at t=1), the Driscoll has
worked well for me. I have been able to reach ADEV
= 10^-11 at 100 MHz at using suitable resonators.
Rick
But one won't be able to use the power right out of the crystal
for anything. So it will have to be amplified & buffered.
If you can do that without lifting the noise floor, then
you've got to ask yourself one question :-)
Why don't I use that little wonder for the sustaining amplifier, too?
And - why do I divide the precious crystal power between the 2
amplifiers at the location where it hurts most: where the level is smallest?
When you compare the Driscoll and the Burgoon (sp??) output
coupling through the crystal, you see it is exactly the same.
One might even apply the current step up trick from Burgoon.
The current through the drains/collectors is enforced by the
crystal, operating into a near-short. Off-resonance the transistor
has complete negative feedback and no gain.
On the output side of the buffer, losing a dB or two for sustaining
the oscillation does not hurt.
A thing I do not like about the typical Colpitts is that it is never
on the series resonance of the crystal. That means that
the feedback divider is part of the resonance which increases
the number of critical parts.
In the Driscoll, the sustaining feedback is quite a wideband thing
and mostly decoupled from the sharp crystal resonance.
regards, Gerhard, DK4XP
On 2/6/2017 4:35 AM, ka2...@aol.com wrote:
Not quiet, using the crystal also as filter gives much better numbers
,,,,,
73 de Ulrich N1UL
In a message dated 2/6/2017 7:30:33 A.M. Eastern Standard Time,
rich...@karlquist.com writes:
I would say the 2 stage "Driscoll" oscillator is the
way to go. I have had good luck with it up to 100 MHz.
The first stage has the crystal in series with the
emitter, but is otherwise a grounded emitter stage.
The second stage is in cascode as a grounded base.
The important operating condition is that only
the second stage limits. First publications on
it were in the early 1970's (search Michael Driscoll).
Rick Karlquist N6RK
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