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

[Tom Van Baak]

 > so if I mess up, please put me straight, gently

Everything looks fine with your posting. You obviously have done a lot 
of work. Thanks for posting.

 > can I just add a PDF as an attachment to this mail
 > and will everyone then see it?

Yes, PDF attachments work well. Also JPG, PNG, GIF, etc. If a block 
diagram or plots would help us understand your design and results, that 
would be great.

/tvb
Moderator, time-nuts


On 10/1/2020 1:33 AM, Joe & Gisela Noci wrote:
> 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
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