For amateur use, PPS comparison requires less equipment and can be more
accurate than trying to measure RF rates like 10 MHz.
When comparing two PPS signals, phase slips are very infrequent so you
can observe drift rate over minutes/hours/days with an oscilloscope or
simple time interval counter to get much better resolution than most
frequency counters can provide. (Of course, a GPS works as well for
this as a GPSDO, albeit with more short term jitter.)
John
----
On 12/18/2016 08:33 PM, Bob Stewart wrote:
Hi Jim,
Thanks Jim,
So, what I'm seeing so far, assuming I'm interpreting it correctly, is big
budget commercial and government applications, generally clustering around
time-controlled multiplexing, as well as the niche that is the space industry.
Then there's the hobbyist, such as Eric who wants to control a Fedchenko clock,
or similar type of application, such as whatever sort of spread spectrum that
ham radio may morph into, or perhaps the low S/N EME guys. Any others?
Bob
From: jimlux <jim...@earthlink.net>
To: time-nuts@febo.com
Sent: Sunday, December 18, 2016 6:56 PM
Subject: Re: [time-nuts] 1PPS users?
On 12/18/16 3:16 PM, Bob Stewart wrote:
One thing I've never really understood is who actually uses the high-quality
1PPS output from a GPSDO. I have spent a lot of time, effort, and money on
developing my GPSDO without a whole of thought to the user base. It was just a
quest for the best result I could obtain with a particular technology. The
frequency standard users was a no brainer. Everyone who wants a frequency
standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.
And that's all I thought I had: a good frequency standard. And then Tom
prodded me a bit and showed me the shortcomings of what I was doing, and I did
something about it. So, if an NTP user can get his time fix directly from a
noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse?
Anyone who needs to trigger events at a precise time or log the
occurrence of an event uses the 1 pps - the serial port (or other
interface) gives you the "at the tone the time will be" message, and the
edge of the 1pps is the "tone".
I've got several systems flying in space (or soon to fly in space) that
use the 1pps from GPS to calibrate their internal clocks and/or to
provide an absolute time reference (along with the aforesaid time message).
For example, one needs to have your carrier frequency within a certain
tolerance for communications with the ground stations: you can either
fly a precision oscillator with an oven (big, heavy, high power) or you
can measure a not-so-precision oscillator (small, cheap, low power)
against a 1pps, and adjust your frequency that way.
I grant you that this is really more like *building* a GPSDO than
*using* a GPSDO.
I've used the 1pps from a GPSDO as a common trigger to synchronize
timing and timestamping for separate systems.
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