[time-nuts] Re: CTI OSC5A2B02 OXCO testing

[Reginald Beardsley]

Tom, 

Thanks. Typo is correct. I didn't describe the data properly.

Those are a single measurement on 10 OXCOs to determine the 10 MHz bias voltage requirement for each. I was adjusting the PSU voltage which is rather coarse, to get close to 10 MHz (within 1 Hz) and measuring the actual voltage with a 34401A.

The purpose is to calculate what precision, low temp co resistors I need to set the Vref for each oscillator. With particular care to try to make it neutral at a convenient temperature. Those resistors are seriously not cheap. The Vishay 50 ppm/C precision foil trimmers ar $25.

The 5386A was running on the internal XOCO as I simply wanted order of magnitude values for each OXCO. So an accuracy of ~2 ppb (5386A and DUT) for time and <50 ppm for voltage.

I'll run the same series with a better reference for Vref so all are tested for frequency at 2 V input to Vref.

Reg     On Sunday, June 4, 2023 at 11:35:11 AM CDT, Tom Van Baak via time-nuts <time-nuts at lists.febo.com> wrote:  
 
 Reg,

Thanks for posting your 10 points of raw data. That will help debug the 
problem. I made two plots for you.

Your first point (at 1.5819 V) doesn't look correct so I ignored that. 
The 8th point (at 23708 V) looks wrong -- 24 kV is kind of high for an 
OCXO -- so I changed it to 2.3708 guessing it was just a transcription 
error.

Plot reg-1.png -- For EFC testing of a good oscillator the points tend 
to fall very consistently along a path and the path is often a line or a 
slightly curved line. See [1] for an old example. But your data is quite 
scattered. That might indicate that either your voltage source is very 
unstable or your oscillator is unstable or even your frequency counter 
is unstable. Or something as mundane as loose wires or noise or trigger 
error.

I would suggest before investigating EFC further that you strive to get 
clean readings. Perhaps set the EFC to a fixed value, maybe use a 1.5 V 
battery, and then collect 10 frequency readings in a row. They should 
all agree to 0.1 or or 0.01 Hz. If so then your counter is not the 
problem. BTW, what is your counter gate time set to?

Plot reg-2.png -- For the 2nd plot I sorted your data and connected the 
dots. Again this should be linear or approximately linear. You can see 
the reading (1.7740 10.00000050) is completely out of place suggesting a 
problem with your setup. And the 2 or 3 points at the top end don't look 
right either.

/tvb

[1] http://leapsecond.com/pages/tcxo-efc/


On 6/3/2023 1:40 PM, Reginald Beardsley via time-nuts wrote:
>Â  
> Here are the results of my preliminary test using just a bench supply and 5386A on the internal XOCO. I just adjusted the Vref until I got within 1 Hz. PSU is settable in 10 mV steps. Data are from my 34401A.
>
> Vref MHz
> 1.5819 10.000000??
> 1.7758 10.00000015
> 1.6924 10.00000010
> 1.7740 10.00000050
> 2.0853 10.00000047
> 1.9374 10.00000040
> 2.1520 10.00000075
> 23708 10.00000073
> 1.9942 10.00000046
> 2.6832 10.00000065
>Â  Â  
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