K1 VFO drift

[Michael Babineau]

Folks :

A little while back I mentioned on this list that I felt that I was
having some frequency
drift issues with my K1 since I had changed the VFO tuning range from
wide to
narrow. I decided today that it was time to see if I could do something
about it,
but I figured that I needed to quantify the magnitude of the drifting
first otherwise
I wouldn't  know whether I have made things better or worse.

I hooked my K1 up to a well regulated 13.8 V supply, turned it on, tuned
it to 7.040 MHZ, started a timer and let it be. Note that the rig was
inside the
air-conditioned house at a temperature of 24c and not subject to any
vibration.

Here is what I observed

time: 5  min   total drift: -200hz  (freq 7039.8 mhz)
time: 30 min  total drift: -300hz  (freq 7039.7 mhz)
time: 60 min  total drift: -300hz  (freq 7039.7 mhz)

So it appears that I am getting approximately 300hz drift down in
frequency
in the first 30 minutes and then things stabilize.

I checked the Specs in the front of the manual and it says < 200 hz /
hour after a 5
minute warm up at 25 degrees C so I guess that technically things are
within spec
as I am seeing only about an additional 100hz drift within the first
hour, after the initial
5 minute warm up.

It is likely that the drift is greater in a less controlled
environment, especially outside with the
brutal heat we have been having here this summer.

I'm still wondering if replacing C2 (68pf disc cap) with a polystyrene
or even
an NP0 cap might make things a bit more stable when using the rig in
the field.
Does anyone think that this is worth doing? Comments?

Michael VE3WMB

P.S. Someday I would love to see an upgraded K1 (lets call it K1.5)
with a
DDS vfo like the KX1 and a continuously variable IF filter bandwidth
like the KX1
or the ABX on the Sierra.



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[EricJ-2]

I operated FOBB 2005 with my K1 in 100F (38C) heat in the shade. At one
point, without really realizing it, the K1 was in direct sunlight filtering
through the trees. The top of the case was very uncomfortable to touch.
Obviously, I didn't do any objective testing to see how that affected drift.
I can only say they during the contest, at no time did I notice any drift on
received signals. Ordinarily, I try to protect the K1 from temp extremes in
the field by keeping it shaded so I was quite sensitive to my neglect when I
noticed it and specifically looked for drift on received signals. It was
fine.

It would be fun to experiment, but I'm not sure it would be very fruitful.

BTW, I just got a KX1 with DDS. I hope the K1 design stays just as it is. At
10hz, the KX1 tunes very smooth, but very slow. With only 3 digits you
quickly lose a sense of where you are on the band if you like to tune around
a lot like me. At 100 hz, it is VERY annoying to tune CW, particularly on a
busy frequency with the cacaphony of discrete tones produced as you tune.
However, at 100 hz you have a better indication of where you are on the band
as 3 digits are sufficient.

I think the KX1 is an excellent answer for those wanting a small rig where
portability is more important than operating efficiency and convenience. It
will easily become my main camping and biking rig. But I can only paraphrase
what someone else on the reflector said within the last couple of
weeks...getting the KX1 makes me really appreciate my K1...which is going
mobile.

Eric
KE6US
www.ke6us.com

K1 1976
K2  567
KX1 539 (purchased from K7MW who did a nice job of building it)

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of michael
Sent: Tuesday, August 09, 2005 9:57 AM
To: [hidden email]
Subject: [Elecraft] K1 VFO drift

Folks :

A little while back I mentioned on this list that I felt that I was having
some frequency drift issues with my K1 since I had changed the VFO tuning
range from wide to narrow. I decided today that it was time to see if I
could do something about it, but I figured that I needed to quantify the
magnitude of the drifting first otherwise I wouldn't  know whether I have
made things better or worse.

I hooked my K1 up to a well regulated 13.8 V supply, turned it on, tuned it
to 7.040 MHZ, started a timer and let it be. Note that the rig was inside
the air-conditioned house at a temperature of 24c and not subject to any
vibration.

Here is what I observed

time: 5  min   total drift: -200hz  (freq 7039.8 mhz)
time: 30 min  total drift: -300hz  (freq 7039.7 mhz)
time: 60 min  total drift: -300hz  (freq 7039.7 mhz)

So it appears that I am getting approximately 300hz drift down in frequency
in the first 30 minutes and then things stabilize.

I checked the Specs in the front of the manual and it says < 200 hz / hour
after a 5 minute warm up at 25 degrees C so I guess that technically things
are within spec as I am seeing only about an additional 100hz drift within
the first hour, after the initial
5 minute warm up.

It is likely that the drift is greater in a less controlled environment,
especially outside with the brutal heat we have been having here this
summer.

I'm still wondering if replacing C2 (68pf disc cap) with a polystyrene or
even an NP0 cap might make things a bit more stable when using the rig in
the field.
Does anyone think that this is worth doing? Comments?

Michael VE3WMB

P.S. Someday I would love to see an upgraded K1 (lets call it K1.5) with a
DDS vfo like the KX1 and a continuously variable IF filter bandwidth like
the KX1 or the ABX on the Sierra.



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_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
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Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com