Depends upon the results you are trying to achieve. Using Linux pretty much
guarantees that your server clock will be off by 6-10us, with substantial
variance. Even with a good nic that supports hardware timestamping, the
variance will increase substantially as you go off box (spread spectrum is
(I suspect this is drifting from the original thread too much, so new
subject)
Temperature ranges from 65F to 78F, with the potential for drafts, but
is more typically 76F.
I read about the NTPsec runs with insulating a Pi and running a load
generating program to better maintain a stable cor
> From: Attila Kinali
> Basically, all you have to do is use an SBC that runs linux and has
> a GPIO with an interrupt to act as a PPS input. Attach a GPS receiver
> and you are almost done. The cheapest option are probably the i.MX233
> based ones (go as low as €20).
Thank you, Attila, this sou
> I'm intending to add a "precision" (well, precision to the Pi world) RTC to
> my Pi 3 to use for a holdover source when it hasn't got PPS from the GPS
> module.
> An RTC that +/- 3 PPM over 24 hours would be great for holdovers of one to
> 20 minutes.
Run some experiments to collect some
> From: Bob kb8tq
> Working all this back into a holdover spec in an unknown temperature
> environment is not at all easy.
> Bob
This is true, it is too easy to multiply figures from the datasheet and then
start believing in them.
We did extensive testing of real units in real life before com
I'm stuck with a near ground level antenna site (~16" above grade?),
with half a sky view (thankfully to the SSE), less some low blocking
buildings with regular mutlipath, plus multipath bouncing off a taller
building to the SE that bounces sats from the NW at me from low over the
Bering Strait
On 10/31/17 1:47 PM, Bob kb8tq wrote:
HI
TCXO is a very loosely defined term. A part that does +/- 5 ppm -40 to +85C
is a TCXO. A part that does +/- 5x10^-9 over 0 to 50C may also be a TCXO.
Dividing the total deviation of either one by the temperature range to come
up with a “delta frequency p
Hi
Under what conditions would you expect to loose GPS? I seem to be able to
do just fine sitting in an armchair here in the family room. That’s hardly a
fancy setup.
Bob
> On Oct 31, 2017, at 10:27 PM, MLewis wrote:
>
> I'm intending to add a "precision" (well, precision to the Pi world) RT
I'm intending to add a "precision" (well, precision to the Pi world) RTC
to my Pi 3 to use for a holdover source when it hasn't got PPS from the
GPS module.
On 31/10/2017 10:04 PM, Chris Caudle wrote:
On Tue, October 31, 2017 7:19 pm, MLewis wrote:
...the "better" quality RTCs seem to be DS32
I don't know of any "non-historic" NTP implementation that even attempts to
drift correct the RTC clock.
Now, the RTC clock is useful to set the time at boot before ntpd gets
started.
Tim N3QE
On Tue, Oct 31, 2017 at 8:19 PM, MLewis wrote:
> If one is building a GPS disciplined NTP Stratum 1 s
On Tue, October 31, 2017 7:19 pm, MLewis wrote:
> ...the "better" quality RTCs seem to be DS3231 based
> How does one translate that into an expected 24 hour holdover?
For the RTC, or for an NTP server? If the NTP server is running it will
not make a difference, modern operating systems do not us
At the moment, my plan is to not support hold-over at all. If GPS doesn’t have
a fix and I’m not getting PPS pulses, I intend to either jump immediately to
stratum 16 or just not respond.
> On Oct 31, 2017, at 1:03 PM, Attila Kinali wrote:
>
> Hoi Leo,
>
> On Sat, 28 Oct 2017 11:14:08 +0100
>
HI
> On Oct 31, 2017, at 8:19 PM, MLewis wrote:
>
> If one is building a GPS disciplined NTP Stratum 1 server from a Pi or
> Beaglebone, the "better" quality RTCs seem to be
>
> DS3231 based (DallasSemi/Maxim), Accuracy ±2ppm from 0°C to +40°C, ±3.5ppm
> from -40°C to +85°C
>
> or
>
> NXP:
If one is building a GPS disciplined NTP Stratum 1 server from a Pi or
Beaglebone, the "better" quality RTCs seem to be
DS3231 based (DallasSemi/Maxim), Accuracy ±2ppm from 0°C to +40°C,
±3.5ppm from -40°C to +85°C
or
NXP:
PCF2127AT: ±3 ppm from -15 °C to +60 °C
PCF2127T: ±3 ppm from
On Tue, 31 Oct 2017 21:03:05 +
Leo Bodnar wrote:
> The goal was maximum throughput with minimum time offset.
> Maximum throughput eventually ended up as "fully saturated full-duplex
> 100BASE-TX" and minimum time offset as "below 1 microsecond"
> There was nothing on the market below £2-3k t
http://www.theregister.co.uk/2017/10/31/google_gnss_analysis_tool_accurate_to_nanosecond_movements/
I wonder how well it works on a $20 Android tablet / phone?
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> From: Attila Kinali
> True. An NTP server does not need to measure time better than 100ns or so.
> 10ns is probably more than good enough. But then, this raises the question
> what your performance metric is that you optimize for?
The goal was maximum throughput with minimum time offset.
Maximu
HI
TCXO is a very loosely defined term. A part that does +/- 5 ppm -40 to +85C
is a TCXO. A part that does +/- 5x10^-9 over 0 to 50C may also be a TCXO.
Dividing the total deviation of either one by the temperature range to come
up with a “delta frequency per degree” number would be a mistake.
Hoi Bert,
On Sun, 29 Oct 2017 08:06:37 -0400
Bert Kehren via time-nuts wrote:
> Thank you for posting the link to Richard's excellent paper that does not
> only apply to Cs. In my opinion it is a must read for any one serious in
> doing any work on time and frequency issues.
Well, the way h
Hoi Leo,
On Sat, 28 Oct 2017 11:14:08 +0100
Leo Bodnar wrote:
> > From: Attila Kinali
> > Can you tell a little bit how your device looks like on the inside?
>
> GPS is a Ublox. MCU is Cortex-M7 and does not run any OS - just main loop
> with prioritised interrupts. Network stack is hand-ma
Hi,
The HP5335A with it’s about 1 ns single-shot resolution is with 9 digits at 1
s. The beauty of it is how you just turn a knob to balance read-out speed vs.
resolution. It remains one of the user-friendliest counters I’ve worked with.
The averaging allows to extend beyond the time-base lengt
Thanks for the help on the HP 5335A!
Richard
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Hi
One of the most user friendly ways to get a 5334 or 5335 to display max
resolution
is to put in into a math function mode. Subtract out the nominal center
frequency of
the source and just look at the “delta” from that center.
Regardless of the tricks, these counters will not give you 12 re
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