[time-nuts] GPS lock of the FE5680. Current experiment and question

paul swed paulswedb at gmail.com
Sat Feb 11 00:09:46 UTC 2012


Good comments so I am on target in thinking.
Why 24 bits because it was pretty easy using 74hc596 8 bit counters with
latch and tristate outputs.
Unfortunately the schematics are on paper at the moment scribbles.
But the cntrs are stacked on top each other as a unit and soldered
together. Only a few pins are not such as clock output enable and such its
quite simple. The 8 bits feed a port on the micro so I can get the bytes.
As for smaller countes indeed at this point its clear it could have been
even 1.
But thats the fun of doing it.
Regards
Paul.

On Fri, Feb 10, 2012 at 6:52 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> I think you will need some sort of analog detector to get what you are
> looking for.
>
> Bob
>
>
>
> On Feb 10, 2012, at 6:34 PM, Chris Albertson <albertson.chris at gmail.com>
> wrote:
>
> > On Fri, Feb 10, 2012 at 2:53 PM, paul swed <paulswedb at gmail.com> wrote:
> >> Just for fun have built up a simple multi-chip project to try my hand at
> >> locking the FE5680 using the external efc connection mod. mentioned in
> >> time-nuts. Typical counter micro rs 232 port stuff.
> >>
> >> Essentially the system is 2 X 24 bit counters that toggle back and
> fourth
> >> every interval selectable from 1 to 65000 seconds accumulating counts.
> I am
> >> measuring the 10 Mhz of the RB and using a novatel superstar II GPS
> rcvr. I
> >> do have a better timing rcvr but this was handy and at this point most
> >> likely good enough.
> >
> > Do you ever need such a large counter?  As you say the counts are only
> > small integers.   If the two are close they would not overflow even a
> > 4-bit counter.   One way to go is to have only a two bit counter (just
> > a pair of flop flops) and end the integration as soon as the second
> > bit flips.  If you are building a FLL you only need to know which is
> > faster.
> >
> > If you want faster convergence I think you have to measure relative
> > phase and use a PLL.   Then you don't need to wait for a full cycle.
> > Maybe only a few degrees of phase difference is enough
> >
> > My plan is to use the 74HC4096 is the detector.  It has the required
> > flip flops inside.  Use that to dive the RB5680 and then when they are
> > reasonably close the 74HC4096 also contains an XOR type phase
> > detector, so switch to that.
> >
> > Chris Albertson
> > Redondo Beach, California
> >
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