[time-nuts] Linear voltage regulator hints...

[Charles Steinmetz]

Dan wrote:

>My gut feeling is you are right about the GPS time base being 
>sensitive. It would be fun to hack into this and try clocking it off 
>the OCXO, but I'm not there yet! :)

One interesting way would be to use the disciplined OCXO output to 
drive a DDS synthesizer set to the GPS unit's clock frequency (which, 
I'm assuming, is not the same as the OCXO frequency).  This approach 
has a number of potentially large problems (delay, spurs, DDS 
resolution, to name just 3), so I'm doubtful that it would work well 
-- but I do think it's worth trying, just because it's so simple and 
cheap ($3.85 ebay DDS board) and potentially instructive.

>I might try some good old 'overkill' and put the GPS in it's own 
>heavy aluminum box. It's been a thought for a while, and should 
>address the thermal integration and time constants you referred to.

Insulate the GPS card from the box (use nylon or teflon standoffs 
with no "through" metal screws), and insulate the box from anything 
solid (same way); i.e., only air can change the box temperature, and 
only air can change the GPS card temperature.  Signals and power 
should go through bulkhead connectors and feedthrough caps on the box 
walls, with "pigtails" to get from there to the GPS card.  You 
probably don't need anything too massive, just whatever cast Hammond 
box it will fit in (allow for the connectors and feedthrough 
caps!!).  You can always add mass later (bolt slabs of aluminum to 
the outside of the box) -- but in this application, you shouldn't need to.

Best regards,

Charles