Argosy VFO Drift

James Bell
Mon, 27 May 96 11:31:49 -700

After 30 min warm-up,my current Argosy drifted +500hz in the 
next 1/2  hr.
 This positive change indicated an effective decrease in 
capacitance due to heat build up.
 The test was done in an remote room of my basement where temp 
is constant and there are no circulating air currents.
 After several days of experimenting, I found the following
 I removed C32 (150pf n080) from the vfo board in the inside of 
the vfo box and replaced it on the foil side of the VFO  pcb
 with a 150 pf np0 capacitor.This "zero "drift capacitor did
the job. 
After an over nite cool off a check of drift excursion shows
+/- 20hz in the 1 st hr from a cold start and then at -20 hz
over the following 1 hr period.
 Anyone wishing to improve the drift characteristics of their
 rig should ensure that they are testing in a stable environment
and remove the S-Meter bulb from the set  before attempting to 
measure frequency drift.(The bulb generates heat). The frequency
 readout in the stock Argosy is not accurate enough to measure 
drift as it does not have enough digits. A separate frequency
 counter must be used and allowed to stabalize its own drift 
for some time before the test.