[Elecraft] Freq dirft in crystals explanation.

[James Hammons]

    Years ago I worked for a company that made crystals and filters.
We made the filters that went into the telemetry that was on the Lunar
Lander for example.  It's been a long time but here goes.
    The K2 uses voltage controlled crystal oscillators for the
synthesizer and BFO.  The varactor diodes,the inductors, the voltage
source and the crystals all change with temperature to some extent.
KI6WX and others measured the frequency drift of 8 K2's and found them
all to drop in frequency with temperature.  The frequency change he
found is generally within the range of the specs I found on the
internet for other radios without TCX0's,  Meaning the vast majority.
So it satisfies most users.
    The crystals used are no doubt AT cut crystals which can have a +
or - change with temperature depending on the angle they are cut from
the crystal with respect to the molecular structure.  For example a
35degree21minute cut gives 0 change in frequency over a wide range
each side of room temperature.   changing the angle by 7 minutes less
produces a + change of about .0015% in 10 degree centigrade.
Increasing the angle produces a - change.   A minute of arc is about
equal to one inch at 100 yards.  So control of this angle is
difficult, which means more expensive.  But a crystal supplier can do
it.
     By chance your crystals may tend to correct more or less the
drift of the other components in the circuit.  KI6WX and I ended up
with one of the worse examples, drifting about 150hz at 14mhz on
warmup. =20
     KI6WX improved his K2 to about 65hz with his compensation mod.
Compensation could be done by selecting a matching crystal, not
practical on the individual level.  Or by having the CPU or another
CPU measure the temperature and compute the compensation needed. =20
How much would that be worth as an add on?=20

James Hammons