[time-nuts] 1PPS for the beginner

Bernd Neubig BNeubig at t-online.de
Tue Aug 14 14:52:50 EDT 2018


Another question, a bit off the road of this thread: 
Is there any common practice for the duty cycle of the 1 PPS pulse?
I have seen devices having extremely short 1 PPS pulses with duty cycles of a few percent or less and others with close to 50% duty cycle.

Best regards
Bernd
DK1AG

-----Ursprüngliche Nachricht-----
Von: time-nuts [mailto:time-nuts-bounces at lists.febo.com] Im Auftrag von Bob kb8tq
Gesendet: Dienstag, 14. August 2018 17:05
An: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Betreff: Re: [time-nuts] 1PPS for the beginner

Hi


> On Aug 14, 2018, at 10:33 AM, Ron Bean <time at rbean.users.panix.com> wrote:
> 
>> A normal GPS module generates it \200\231s outputs off of a free 
>> running internal clock. Generally this is a TCXO in a
>>  \200\234timing \200\235 GPS ( = one that puts out a rational PPS).  
>> This i bit counter intuitive, since you would *think* they phase lock 
>> the local source in the module. They don \200\231t mainly because it 
>> makes the math easier.
> 
> Is there a need to make the math easier?
> This is what we have microprocessors for.

There is *always* a need to make the math easier if I’m quickly typing up an example. For proof I reference the hundreds of posts in the archives where I didn’t quite get it right :)

Indeed, the real numbers could be just about anything. They are highly dependent on what’s in the specific module. In some cases, the clock involved is well over 300 MHz. 

Bob

> 
> Thanks for the "hanging bridge" explanation. It would be nice if 
> someone had a time-nuts-glossary that included various terms that come 
> up on the list, like "hanging bridge", "spurs", "sawtooth correction", 
> "GPS allan ski jump", etc.
> 
> Is there a time-nuts FAQ?
> 
> 
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