Dave;
I designed the K2 VFO stability mod that is now included in all K2's.
Variations in the crystal stability cause each K2 to drift slightly
differently. That's why I included the instructions on how to adjust the
resistor values to minimize the K2's drift.
I tested my K2 from 15C to 45C in a home built environmental chamber (use
one of those thermoelectric cooler/heaters from WalMart or Target). I
picked the resistor values to produce the minimum drift over an assortment
of crystals that Elecraft sent me. I also adjusted those resistor values to
achieve minimum drift in my K2.
Over that temperature range, my K2 shows a maximum drift rate on its worst
case band of 15m of 1.8 Hz/C. The average drift rate is less than 1 Hz/C.
The K2 warmup internal temperature change is 5C. On 20m, my K2 will show a
warmup drift of about 5 Hz. This shows what you can achieve if you run a
careful set of experiments with different resistor values.
I only know of a few people who have actually adjusted the resistor values.
It is a long time consuming process with very careful data measurement.
However, you can reduce your drift rate following the printed procedure.
-John
KI6WX
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <Elecraft@mailman.qth.net>
Sent: Wednesday, March 15, 2006 1:58 PM
Subject: [Elecraft] K2 frequency drift
Two questions for the group:
1. My K2, serial 5120, has worked flawless since I built it last
fall...except that about a week ago, friends on a 20m net I work daily said
I was low about 40 Hz in frequency. (Frequency calibration checked
occasionally against both my external counter and WWV had been right on.) I
transmitted first maybe 2 minutes after turning the rig on. So I dialed up
about 40 Hz (.04 kHz) to get on frequency. In the next 15 minutes, I had to
move the indicated frequency down slowly to the exact net freq. Drift was
the obviously the problem.
Since then, I've turned the K2 on early and found that by net time, it was
on the exact frequency on the LCD. However, just after turning it on (room
temp constand at about 68F), tuning WWV on 10 MHz (equalizing the stations's
audio tone on USB and LSB) shows I'm low by 40-50 Hz, drifting up to
indicated freq. in 15-20 minutes.
I know that resistors RA and RD on the thermister board control drift rate,
and some months ago there were comments here on how to compensate, but I
didn't retain the thread. Anybody care to provide that advice again or new
comments?
2. I'm currently building a KPA100 internal amplifier kit, and I'm wondering
if the added heat creates drift or frequency calibration problems.
Dave Martin
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