[time-nuts] First success with very simple, very low cost GPSDO

Chris Albertson albertson.chris at gmail.com
Thu Apr 10 23:05:24 UTC 2014

On Thu, Apr 10, 2014 at 10:55 AM, Charles Steinmetz
<csteinmetz at yandex.com>wrote:

> Why even try to discipline an OCXO before it's warm?  Just leave the
> control loop off for a predetermined time at startup.  You can light up a
> bright red "unlocked" LED, and even inhibit the 10 MHz output until lock is
> achieved if you want.

Even if you wait long enough you still need to set the DAC to "something"
as a first try.    What if your first guess is off by a large amount.   The
answer is not to guess better because you still need some way to determine
if the guess is correct.

> Alternatively, you could figure out the EFC voltage needed to zero the
> cold oscillator

How to do that?  Can you write code to do this without counting overflows?
 You can be off by 256 cycles and never know it.   Let's assume someone is
building a GPSDO because they need a frequency reference and don't have
one.  A good assumption, I think.   How could such a person "figure out the
EFC voltage needed"  with out either coining cycles?

I'm thinking about turning the overflow counter off after lock.  But
without one I think we have a chicken and egg problem where you would need
an accurate frequency reference to build a GPSDO.


Chris Albertson
Redondo Beach, California

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