[time-nuts] Assistance needed to understand some V_OCXO stability concepts.

[Joe & Gisela Noci]

Good Morning all.
I am new to the group, very green as to how the group/mailing, etc works,
so if I mess up, please put me straight, gently...!
I do not have much experience or knowledge in this field, but have spent
the last year or so building a GPDSO and need some help in understanding
the results I get - they seem to good to be true, so I suspect it's not
true!
I have built the unit based on the Brooks Shera concept, with some changes
in collaboration with Jeff, K6JCA.
To describe it would be best done by means of a block diagram ( can I just
add a PDF as an attachment to this mail and will everyone then see it?). In
essence - a UBLOX M7N GPS provides a 1PPS signal which controls a pulse
width detector, fed from the HP_00105-6013 OCXO ( pulled from a defunct
HP-5061A) . This pulse width is converted to a DC level, into a D/A. A uP
then drives a 16bit DAC to control the Varicap drive to the OCXO.
I have measured the KV of the OCXO to be close to 0.03Hz/volt.

The DAC drive is derived for a set of software filters, first is a 32tap
FIR, for initial stabilization, then into IIR filters of increasing time
constants, 30sec, 100sec, 200sec, 400sec.

I log plots of the pulse width detector, DAC voltage, Oven temp, and many
other parameters.
I do not have any fancy equipment to measure Adev, etc, nor any accurate
frequency counters...
NOTE - The OCXO is a 5MHz unit, but I double to 10MHz and the ref clock to
the pulse width detector is 10MHz/10 = 1MHz. So the pulse counter has a max
period of 1us.

I understand the  KV of the OCXO works out to 3ppt / millivolt (from the
0.03 Hz/volt).
When I run the unit, it locks very well, and while running with IIR4 active
( 400sec) is observe the following:
The DAC output voltage curve shapes closely resembles the temp control
voltage to the oven - as I would expect.
Over a 24hour period the oven control voltage varied by 0.5 volts. The
total DAC voltage during this varies by 36millivolts ( Is that 0.108ppb in
delta freq?)
Over a specific period of 3 hours ( afternoon), where the temp control
voltage varied by less than 200millivolts, the DAC output varied by
10millivolts ( is that 30ppt ??)

Please forgive my questions - I lack the knowledge to know if I am asking
the right questions!

I can post some plots if it will help folk explain what I should be asking!

Thank You
Joe
V51JN, Swakopmund
Over a