[time-nuts] FE-5680A Results so far

Bob Smither smither at c-c-i.com
Wed Dec 28 15:07:55 EST 2011

Chuck Forsberg WA7KGX N2469R wrote:
> I haven't checked it, but the FE5680A has 1pps on pin 6.
> There is no documented way to sync the FE5680A 1pps to an external 
> reference.
> You could set an extreme value in the freq offset and wait for the 1pps 
> to drift
> into place.

On mine if you put in extreme offsets it seems to lose sync.  Not sure if this 
is typical.

To adjust the phase between the GPS 1 PPS and the 1 PPS derived from the 
FE-5680A I put a switch in the divide by 1E7 logic used to get a 1 PPS from the 
FE-5680A.  Pushing the switch changes the divide so that the 1 PPS can be slewed 
to a known phase WRT the GPS 1 PPS.

> Measurements of the delay between 1pps signals depend on the accuracy of 
> the measuring
> device - e.g., the timebase in the counter of oscilloscope X axis.

Yes, but for a time interval of (for example) 100 usec even a very poor counter 
timebase would be accurate to sub nsec.  Of course, the FE-5680A could be used 
as the counter timebase :-).

> On 12/28/2011 10:45 AM, Bob Smither wrote:
>> Chris Albertson wrote:
>>> Just got my fe5680 yesterday.   Seems to work but the fe5680 is the most
>>> accurate reference I have.  So how to test it?   I plan to buy a
>>> Thunderbolt but until then, anyone have any creative ideas?
>> <snip>
>>> Going to have to get a Thunderbolt.  I have an Oncore UT+ the provides a
>>> good pulse per second but that will not help
>> You can take the FE-5680 10MHz and divide it down to a derived 1 PPS.  
>> Use the time interval measurement on your HP5328A to measure the TI 
>> between the Oncore 1 PPS (start) and the derived 1 PPS (stop).
>> You might want to set a finite TI (for example, 100 usec) by adjusting 
>> the phase of the derived 1 PPS so the measurement doesn't get confused.
>> I have done this using an HP5316B with good results.
>> The jitter on the GPS 1 PPS might limit your short term resolution, 
>> but over a day or so you should be able to measure the drift of the 
>> FE-5680A.
>> I have used a Ref Tek 111A GPS clock for the 1 PPS.  That unit has a 
>> lot (several usec) of jitter.  I recently started using a 111C that 
>> has much lower jitter (a few 10's of nsec).  I believe your OnCore 
>> unit will be similar.
>> Here are some results from my tracking my FE-5680A:
>>   http://c-c-i.com/image/tid/4
>> Most recent:
>>   http://c-c-i.com/node/159
>> Hope this helps.
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Bob Smither, PhD                                   Circuit Concepts, Inc.
Those who would give up essential Liberty, to purchase a little temporary
safety, deserve neither Liberty nor safety.
   -- Benjamin Franklin: November 11, 1755
Smither at C-C-I.Com  http://www.C-C-I.Com  281-331-2744(office)  -4616(fax)
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