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

[Bob Camp]

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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