IIRC there are two cascaded voltage regulators before the VFO which
may also be good candidates for improvement. Mine's been more drifty
since I blew the first one; I probably should have replaced the second one
at the same time.
On Wed, 4 May 2011, Matt Scholz wrote:
Hi -
I am
Matt,
I would first suspect the stability of the voltage regulators. That VFO
is tuned with a varactor, if the voltage changes, the frequency will
change. If that does not settle it down, I would wind L1 on a new core
on the suspicion that the present one is more temperature sensitive than
Thanks Don.
So here's another question. My first step was to remove C2, which
effectively removes the varactor (D3) from the equation. I was still
observing an excessive amount of drift. Doesn't this rule out the voltage
regulators as the cause of this problem?
73,
-Matt W6ZBA
On 5/5/11 7:19
Very interesting problem Matt. The VFO in my K1 is stable once it has warmed
up for about 5 minutes,
as long as the rig isn't out in the sun. I have observed some significant
drifting due to physical warming
while operating portable so I now know to keep it shaded.
Sometimes I wish for a K1.5
I'd also suspect the voltage regulator first, but another possibility is
the varactor itself. Many years ago in another universe I was the
product engineer for tuning diodes at a large U.S. semiconductor
manufacturer. Varactors are simply reversed bias diodes with a junction
profile optimized
Matt,
That takes only one of the varactors out of the circuit. You could
remove both C2 and C7 and that would remove both varactors from the
circuit. But that still does not eliminate the supply voltage because
Q8 will still change in response to a change in the 6 volt regulator output.
Don,
Thank you for the very detailed response/analysis - that was helpful. I
definitely will heed your advice and replace one component at a time.
73,
-Matt W6ZBA
On Thu, May 5, 2011 at 11:37 AM, Don Wilhelm w3...@embarqmail.com wrote:
Matt,
That takes only one of the varactors out of the
Hi -
I am trying to reduce my K1's VFO drift to an acceptable level. The VFO
frequency drifts up at a rate of about 30Hz/minute (after a 5 minute warm
up). Even after one hour, the drift is still about 15Hz/minute. This is
too much, obviously.
I have been trouble shooting this with the help of
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