[time-nuts] NCOCXO anyone?

[Richard (Rick) Karlquist]

On 7/24/2016 6:44 AM, James Flynn wrote:
> Hal Murray <hmurray at ...> writes:
>> Has anybody put the DAC and all of the analog stuff inside the oven?
> Seems
>> like an obvious idea so somebody has probably patented it.
>>
>
> I am using a 5 MHz custom built design which has everything inside the
> outer oven in a double oven.
>
> This includes:
>
> Precision regulators for DC supply.
> 24 bit DAC
> Reference for DAC
> All analog devices, resistors and capacitors after DAC.
> All buffer amplifiers from oscillator.
>
> Unit only has raw DC and I2C lines for inputs and 5MHz sine wave out at
> 3 volts p-p.
>
> It also seemed the obvious way to go in the design.

IMHO, it isn't obvious that this is the way to go.
Nor is it a "free lunch" as it seems to be envisioned.
The last thing you want in an oven is a lot of
added thermal overhead, especially in a double oven
where you already fighting against running out of
temperature range.  If you want to ovenize everything
but the kitchen sink, put it in it's own oven that is
separate from the crystal oven.

I also don't like intermingling digital signals with the
analog oscillator signal.

Have you measured the thermal gain of your outer oven?
I suspect it's not much.  You could use inner oven
current draw as a proxy.

Rick