Re: [time-nuts] Lady Heather's Tbolt oscillator auto-tune function
A cold oven freq is off by hundred's by Hz, Much much greater than the range
of the Dac
The TBolt does not start tuning until it's oven has warmed up.
Setting anything in the Tbolt biased on cold start turn-on is counter
productive. It takes days or weeks for it settle down.
At initial turn-on and when returning from a lost signal drop-out if the
phase is off, the Tbolts enters a fast Dac slue tune mode that sets the
phase and then the Freq to zero cross before entering its normal mode.
Because of these, it does not mater in the least what the Dac is set to at a
cold start.
A damping setting in a Tbolt of greater than 2 is not a good idea.
And a TC setting of >1000 is not a good idea unless using the 'extended TC'
mode.
. . .
ws
Actually, for best results from a cold start, it is best to set the
initial DAC voltage to whatever voltage produces 10.000000000 MHz when the
oven is cold.
Bob replied:
.. errr . that's pretty far off :) DAC at 10 or 20 minutes is probably the
target.
No, DAC for 10.000000000 MHz with a stone cold oven is best for cold
starts. This setting is still best even if the oven is partly warm,
because the loop is moving the DAC in the same direction it needs to go
-- it can "catch up" gracefully without racing in the wrong direction in
full saturation to meet the crystal as it warms up, then banging back
and forth from saturation in one direction to saturation in the other
direction before finally leveling out. It is the damped oscillatory
approach to the capture zone, and recovering from saturation (not just
once, but multiple times), that slows things down.
By starting the DAC to produce 10.000000000 MHz from the cold oven, all
that is avoided and the loop just tracks the warming crystal (or, if it
can't quite keep up, at least it is moving in the same direction and can
catch up gracefully without overshoot -- still much faster than starting
from the DAC voltage that produces 10.000000000 MHz with a fully warm oven).
Trust me, I tried all of this experimentally and know whereof I speak.
Best regards,
Charles
Warren wrote:
A damping setting in a Tbolt of greater than 2 is not a good idea.
It is if one is only concerned about frequency stability and accuracy
and wants the best performance that can be obtained at tau < about 10
seconds.
And a TC setting of >1000 is not a good idea unless using the 'extended TC'
mode.
I did not suggest setting the TC >1000. My suggesetion was to set the
"recovery" mode "max offset frequency" (the furthest the Tbolt will
allow the oscillator to go off frequency in order to correct the PPS
phase) in that range. That only affects recovery (speeds it up), it
doesn't do anything during normal operation. It may not need to be
1000, 100 may be plenty. I do not recall exactly where mine ended up.
Best regards,
Charles