[time-nuts] Use the LT3042 for retrofit?

[Bob kb8tq]

Hi

You can either do the math … yuck …. or just try it. It turns out that with a “normal” sort of
EFC sensitivity (< 1 ppm / V) on a “normal” frequency OCXO ( <30 MHz) , the voltage can have a 
bit of noise on it and the phase noise of the device will not suffer. Simply put - you can run it 
with a 78L05 and the phase noise will be the same as with a short. 

Since the phase modulation rolls off as 1/F for a flat noise spectrum, the noise on the EFC 
“chases” the phase noise floor as frequency increases. Toss in an internal bypass on the EFC
line and it goes down even faster. 

If you get into OCXO’s that are more like VCO’s then things aren’t quite so easy….

Now, this is just talking about phase noise. If you look at stability, indeed a finite delta V on the EFC
will change the frequency of the OCXO. Generally, the biggest factor is the voltage drop from the
oven current getting into the EFC “loop”. Its actually pretty hard to keep them separate. Unless 
you can split them apart, they will limit your heroic efforts on EFC stability. Our 1 ppm / V OCXO 
above moves 1 ppb / 1 mv. If you are after a ppt, you need 1 uV of EFC “ground isolation”. 

Bob

> On Mar 20, 2018, at 10:24 PM, Perry Sandeen via time-nuts <time-nuts at febo.com> wrote:
> 
> Yo Dudes,
> Should one consider retrofitting  HP 105's,  Austron 1250's or HP 10811 power supplies with the LT3042 for better performance?  The price is modest.  The HP 10811 suggested PS for the EFC is a 723 circuit that spedc's 6 microvolts ripple IIRC.
> Regards,
> Perrier
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