[time-nuts] Portable standard

WB6BNQ wb6bnq at cox.net
Wed Apr 6 08:03:48 UTC 2011


Joe,

Before you worry about batteries and such, you first need to ask what it is that
you are trying to accomplish.

For instance, if you did not need the really close in low phase noise and really
short term stability, then perhaps a Rubidium (Rb) oscillator would suit your
needs.  the Rb has better longer term stability than a crystal oscillator and can
be left off until it is needed saving on battery requirements.  A decent Rb would
be up to specs in about 20 minutes and would suffice for most applications as a
better general frequency reference for portable purposes.

A really high quality crystal oscillator isn't worth a damn unless it is kept
running constantly and without vibration.  Any banging around is going to
invalidate it.  The Rb, unless you beat it with a hammer, does not suffer from
those problems.  Obviously you would like to treat either item with care, but
things do happen and the Rb would be more rugged the crystal oscillator.

Bill....WB6BNQ


Joseph Gray wrote:

> If I were to buy an HP 10811A OCXO to use as a portable, battery
> powered frequency standard, how would you recommend that it be powered
> and packaged? Assume that the final package would be powered 24/7 and
> sitting on a shelf most of the time. Prior to portable use, it would
> be checked against my GPSDO. Portable use would probably be at worse a
> few days, but more likely less than a day.
>
> I'm thinking of using a couple of 12V, 7AH SLA batteries and float
> charging them. Some charge circuits use pulsing current for SLA
> batteries. Would this affect the OCXO?
>
> Obviously too much air flow will be a problem. Can the OCXO, batteries
> and associated circuitry be sealed in a box with no vent holes (not
> strictly air tight)? What about putting the OCXO in a small styrofoam
> box by itself? Will that cause overheating or other issues? How about
> vent holes in the overall enclosure and baffles around the OCXO to
> minimize air flow?
>
> Should I forget the whole idea and just buy a rubidium?
>
> Joe Gray
> W5JG
>
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