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 _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.