[time-nuts] FE-5680A Question

[Chris Albertson]

On Wed, Feb 15, 2012 at 9:12 AM, Bob Camp <lists at rtty.us> wrote:
> Hi
>
> Which still gets us back to - why the really odd sweep on the FE's? and
> should you center the VCXO as a matter of routine maintenance?

I think a very asymmetric sweep makes the most sense.

First some history of sailing ships.   Back in the 1600's navigation
was not perfect and you never knew your exact position on the open
ocean.   Knowing within 30 miles was hard to do.  So to get to a given
location in North America from Europe they typically would aim about
50 or more miles to the north of their intended destination and then
when they reached land would sail south until they found the
destination.   This added a day or more to the trip.   If they tried
to hit the target dead-on they would likely miss but then they'd have
to literally guess wetter to go North or South and if they guessed
wrong it could really be bad so they always headed for enough north of
the target so there was no guessing about which way to turn.

I think the sweep is done the same way.  If you start way low you know
100% which way to go, the lock has to be up.  Seeing as we know they
are using software in the loop this makes sense.

So on pwr up the uP starts looking with bottom up sweeps.   The sweeps
fail to find lock because the temperatures of the crystal and Rb are
to low but after some minutes, finally a sweep finds the lock

Chris Albertson
Redondo Beach, California