[time-nuts] FE5680A Calibration

[Chris Albertson]

On Wed, Mar 14, 2012 at 8:17 AM, Chris Stake <stake at btinternet.com> wrote:
> Hello all,
>
> I purchased a FE5680A from a Chinese  Ebay vendor. I have connected it to a
> 16.5V laptop supply, added 7805-based 5V rail and a PMOS Fet switch to drive
> a LED for the "locked" signal. I can communicate with it using the excellent
> Fe5680Calibrator software. As received the frequency offset is set to Zero
> and the unit seems to work well.

What you need to do is build a GPSDO using your FE5680A as the "O".
You can use digital logic or a human in the control loop.  Either way
it works the same.

Get a 7400 series "flip flop"  A 74AC74 costs about 50 cents.  Wite it
so the PPS for the GPS flips it on and the next edge of the 10MHz out
from the FE5680 re-sets the signal.  A simple XOR can also work.

Now what you do is measure the time the signal is high.  The classic
way is to use the signal to charge a capacitor then measure the
voltage on the cap.  So now you can use a DMM to measure  time.

The controller adjusts the FE5680A's frequency so as to keep the time
the signal is high (and the voltage on the cap) at some arbitrary
fixed value

People have built the above using all kinds of methods, from pure
analog to micro controllers, 7400 logic and even a human in the loop.
   If you want to build a working system fast look at using an Arduino
and divide the 10Mhz signal down by at least 10 or 20 so that (1) the
speed is compatible with solderless breadboards and the flip flop's
output will stay high longer and will be easier to measure.


Chris Albertson
Redondo Beach, California