1PPS users?
One application is advanced network diagnostics eg cards like this:
https://www.endace.com/endace-dag-high-speed-packet-capture-cards.html
So for a 40 GbE card, time-stamping 1 kilobyte packets demands
sub-microsecond accuracy, if you want to compare at different points
in your network.
Cheers
Michael
On Mon, Dec 19, 2016 at 10:16 AM, Bob Stewart bob@evoria.net 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?
Bob - AE6RV
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi Bob,
One thing I've never really understood is who actually uses the high-quality 1PPS output from a GPSDO.
I use it for NTP server, like many others also do around the world.
--
73s!
Esa
OH4KJU
Hi
The vast bulk of all GPSDO’s sold over the last three decades were sold because the first
CDMA specification required that the basestation operate without a GPS signal for
24 hours. During that time the alignment of the Gold Codes is required to be within
10 us of “GPS time”. Once the codes go out of alignment, the cell phone takes an
interference hit, so the the basestation must be shut down.
The time and code alignment requirement has “evolved” over time. Various 3G, 4G, 5G, 6G ..
systems have tighter timing specs (or apparently none at all). Technology has also evolved.
A self contained GPSDO located at each and every transmitter is no longer the only way to do this.
We have 1588 and a number of other tools that didn’t exist in the 1980’s.
Bob
On Dec 18, 2016, at 11:20 PM, Bob Stewart bob@evoria.net wrote:
Hi Scott,
I do understand the reasons that these users want this quality of output. It's who these users are, what fields, industries, etc, that I didn't quite understand.
Bob -----------------------------------------------------------------
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
From: Scott Stobbe <scott.j.stobbe@gmail.com>
To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Sunday, December 18, 2016 8:22 PM
Subject: Re: [time-nuts] 1PPS users?
Part of the reason 1PPS needs to be so clean is because you are continuously integrating phase noise of the LO (hopefully an OCXO). While 10 uS is pretty trivial off a gps receiver. Without gps, 10 us over 24 hrs with a plane jane AT-cut crystal subject environmental dynamics becomes ludicrous. More than likely the short term stability of GPSDO is cleaner than it needs to be for many applications, but that is so holdover over an hour or day remains reasonable.
On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart bob@evoria.net 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?
Bob - AE6RV
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/ GFS-GPSDOs/info
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
You know, there's a reason this list is called "time-nuts" and not
"frequency-nuts" :-).
But sometimes I wonder if "phase-nuts" might be a better term.
It is so incredibly useful to put your best 1 PPS into a scope and use that
to watch for systemic effects on your second-best clock. That's why we then
end up with a third, fourth, fifth, etc. clock :-)
So many newcomer GPSDO makers seem to just do frequency lock but rarely do
they or their users know the difference.
At same time there are so many non-ntpd NTP implementations that just jump
instead of slew the clock.
Tim N3QE
On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart bob@evoria.net 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?
Bob - AE6RV
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/time-nuts
and follow the instructions there.
On Sun, December 18, 2016 10:20 pm, Bob Stewart wrote:
I do understand the reasons that these users want this quality of
output. It's who these users are, what fields, industries, etc, that I
didn't quite understand.
Magnus wrote a paper recently on effects of the GPS time slip (recent
error in data upload) on the broadcast industry which uses GPS time to
synchronize widely separated transmitters so that they can overlap their
broadcast coverage areas without interference.
I believe the power industry is using GPS provided time to stamp power
events for analysis as well.
--
Chris Caudle
On 12/19/16 6:28 AM, Chris Caudle wrote:
On Sun, December 18, 2016 10:20 pm, Bob Stewart wrote:
I do understand the reasons that these users want this quality of
output. It's who these users are, what fields, industries, etc, that I
didn't quite understand.
Magnus wrote a paper recently on effects of the GPS time slip (recent
error in data upload) on the broadcast industry which uses GPS time to
synchronize widely separated transmitters so that they can overlap their
broadcast coverage areas without interference.
I believe the power industry is using GPS provided time to stamp power
events for analysis as well.
And pretty much any of these will ingest a 1pps + message, rather than,
say, a 10 MHz reference.
Why not just use the raw GPS 1pps (which is typically good to a few tens
of ns)? GPS coverage/outage and random variation in the GPS 1pps
A lot of them use a disciplined oscillator to generate the 1pps, so the
oscillator is essentially a long term averager/low pass filter on the
raw GPS output -
I believe the power industry is using GPS provided time to stamp power
events for analysis as well.
Chris,
Yes, in fact one of the first applications of hp's SmartClock was just that:
"Accurate Transmission Line Fault Location Using Synchronized Sampling"
http://leapsecond.com/hpan/an1276-1.pdf
Bob,
For more background on 1PPS and time synchronization see:
"GPS and Precision Timing Applications"
http://www.hpmemoryproject.org/an/pdf/an_1272.pdf
"The Global Positioning System and HP SmartClock"
http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf
Other useful hp app notes for time nuts:
http://leapsecond.com/hpan/list.htm
/tvb
Hi
On Dec 19, 2016, at 10:11 AM, Tom Van Baak tvb@LeapSecond.com wrote:
I believe the power industry is using GPS provided time to stamp power
events for analysis as well.
Chris,
Yes, in fact one of the first applications of hp's SmartClock was just that:
"Accurate Transmission Line Fault Location Using Synchronized Sampling"
http://leapsecond.com/hpan/an1276-1.pdf
There is an FCS paper that pre-dates that by about a decade. The guys at
Quebec Hydro set up GPS to monitor the phase state in their main distribution
network and wrote the paper. I don’t have an FCS DVD handy to dig it up. I
also have no idea if there is a copy outside a pay wall. They went into a bit
more detail on what they saw. It gives you a bit better feel for how it works
in the real world.
Bob
Bob,
For more background on 1PPS and time synchronization see:
"GPS and Precision Timing Applications"
http://www.hpmemoryproject.org/an/pdf/an_1272.pdf
"The Global Positioning System and HP SmartClock"
http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf
Other useful hp app notes for time nuts:
http://leapsecond.com/hpan/list.htm
/tvb
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
From: jimlux
And pretty much any of these will ingest a 1pps + message, rather than,
say, a 10 MHz reference.
Why not just use the raw GPS 1pps (which is typically good to a few tens
of ns)? GPS coverage/outage and random variation in the GPS 1pps
A lot of them use a disciplined oscillator to generate the 1pps, so the
oscillator is essentially a long term averager/low pass filter on the
raw GPS output -
---====
Having the GPSDO/PPS is handy when someone parks outside your location and
carries a GPS jammer.
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
Hi
On Dec 19, 2016, at 11:55 AM, David J Taylor david-taylor@blueyonder.co.uk wrote:
From: jimlux
And pretty much any of these will ingest a 1pps + message, rather than,
say, a 10 MHz reference.
Why not just use the raw GPS 1pps (which is typically good to a few tens
of ns)? GPS coverage/outage and random variation in the GPS 1pps
A lot of them use a disciplined oscillator to generate the 1pps, so the
oscillator is essentially a long term averager/low pass filter on the
raw GPS output -
---====
Having the GPSDO/PPS is handy when someone parks outside your location and carries a GPS jammer.
Unless the jammer causes the GPS receiver to go a bit nuts and the GPSDO is dumb enough to
follow it. Don’t ask how I know about this particular situation :)
Bob
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.