Precision Time Protocol – Windows 10 implementation
From: Adam Kumiszcza
[]
I didn't have to stick to "good enough", David :)
Unfortunately, I will have to move this ntp server to another location (or
make another one and leave this one here). It will not have access to south
facing window there, only west is possible.
Best regards,
Adam
---===
Adam,
I take more of an engineering approach - stop when it's good enough! I have
too many other things which interest me (like frequency measurement) to
spend time past when "good enough" for NTP is achieved. But you might like
to try the Raspberry Pi 4 with a slightly faster CPU, and significantly
better I/O, for enhanced performance.
Particularly as you are using a Raspberry Pi, that's likely to be the
limiting factor, not the number of satellites you can see. For that reason,
I would suggest that a west-facing window (or outside same) would be fine.
Monitor it occasionally, of course.
However, having three or four stratum-1 NTP servers is a good idea,
particularly when they are such a low cost as the Raspberry Pi solution can
achieve. The last few Raspberry Pi zero projects I've housed I've
automatically added a Chinese GPS board, so they become stratum-1 NTP locked
rather than relying on LAN or Wi-Fi sync. With just two, you're never sure
which is right!
Cheers,
David
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
Adam Kumiszcza writes:
After all your tips I just checked whether the roof itself blocks the
signal or not. I put the patch antenna together with a metal disk on top of
a high wardrobe, close to ceiling, and I guess it is the best position
here. See attached screenshots.
Good, that looks more sensible.
Unfortunately, I will have to move this ntp server to another location (or
make another one and leave this one here). It will not have access to south
facing window there, only west is possible.
Since the GPS antennas have a built-in LNA, you can extend the cable
quite a bit if you use something that's not too lossy without impacting
the performance much. The captive cable on these antennas is almost
always the cheapest thing that will work (RG-174 mostly), so I tend to
buy them with the shortest option on offer, then extend with H195 or
LMR400 coax depending on required length and how much space is available
for running the cable. You need to be careful when specifying the
connectors, the GPS antennas are plain SMA (not RP-SMA) and many of the
cables you'll find are for WLAN extension (which mainly uses RP-SMA).
If you need a pair of extensions, look for twin-coax; you can easily
separate the two individual cables and it's usually cheaper than getting
two single cables of the same make and length.
Your other option is running the rasPi headless from a PoE segment, then
you can move it with the antenna relatively easily.
Regards,
Achim.
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
Samples for the Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#BlofeldSamplesExtra
On Mon, 12 Aug 2019 12:05:14 +0200
Adam Kumiszcza akumiszcza@gmail.com wrote:
I cannot see any difference between these positions. I've made 10
measurement for each position, getting 12 SNR values for satellites for
each measurement and then calculated the average of these.
Hanging antenna had 25.18 SNR average (2.21 standard deviation). Antenna on
a ground plane had 26.10 SNR average (2.08 standard deviation).
https://docs.google.com/spreadsheets/d/1lvGFTQS62MqiQALjHmWFZRY3hb5O1OqANFGBhnCaEUo/edit?usp=sharing
SNR is a bad indicator of multipath. Multipath changes the SNR by
at most 3dB. And the change can go in either direction. For GPS L1 C/A
the multipath can affect the timing solution by up to 30ns (IIRC, I don't
have a reference at hand). That's much more than you'd expect from just
a 3dB degradation, and definitely not what you would expect from a 3dB
increase in signal strength. The reason for this is that the multipath
signal is correlated with the signal and affects it differently than just
random noise.
If you want to see what the effect really is, you have to measure the
output of your GPS to a more stable standard (at the very least a good
rubidium vapor cell standard) and look at the variations with a tau
up to 24h. Note that multipath is usually correlated on a 12h/24h basis,
but it is not necessarily a strong correlation as the signal path changes
slightly due to changing satellite orbit and changing lensing effects
of the atmosphere. How much correlation you get depends on a lot of
factors that are not easy to quantify in an uncontrolled environment.
Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
On Thu, Aug 8, 2019 at 7:00 PM David J Taylor via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi everybody! My first post here, I hope the subject is adequate for this
mailing list.
I'm using a tiny layer 1 NTP server consisting of Raspberry Pi 3B+ with
Ublox MAX-M8Q expansion board providing GNSS (currently GPS, Galileo and
Glonass, sometimes I switch to Beidou, too) reference with PPS + a simple
patch antenna hanging near the window. Offset, jitter and rms are most
often smaller than 1 µs. The server is included in NTP pool.
I'm using several Windows 10 machines on the same LAN, all using NTP client
software from Meinberg. The typical offset and jitter in those are about
100-500 µs. I would like to make it lower.
[]
Thanks in advance for any suggestions!
Adam Kumiszcza
---===========
Adam,
You could feed the PPS signal to the Windows PCs as one way of making the
performance better:
https://www.satsignal.eu/ntp/setup.html
Performance:
https://www.satsignal.eu/mrtg/performance_ntp.php#windows-stratum-1
Cheers,
David
Hi again!
My raspi is now in a new location. The GPS signal is fine, the window is
not south-facing, but the antenna is outside the window attached to a metal
windowsill, and there are no buildings nearby.
I'm coming back to the idea of distributing PPS signal. Do you think such a
contraption could work?
https://botland.com.pl/pl/raspberry-pi-hat-komunikacja/11707-serial-pi-plus-max3232-interfejs-rs232-dla-raspberry-pi-7426787870194.html
I mean, stacking it over the uputronics board and soldiering some pins.
The MAX3232 chip is the same as on these kind of devices:
https://www.ebay.com/itm/MAX3232-RS232-to-TTL-Serial-Port-Converter-Module-DB9-Connector-MAX232/262241627343
Cheers,
Adam
From: Adam Kumiszcza
Hi again!
My raspi is now in a new location. The GPS signal is fine, the window is
not south-facing, but the antenna is outside the window attached to a metal
windowsill, and there are no buildings nearby.
I'm coming back to the idea of distributing PPS signal. Do you think such a
contraption could work?
https://botland.com.pl/pl/raspberry-pi-hat-komunikacja/11707-serial-pi-plus-max3232-interfejs-rs232-dla-raspberry-pi-7426787870194.html
I mean, stacking it over the uputronics board and soldiering some pins.
The MAX3232 chip is the same as on these kind of devices:
https://www.ebay.com/itm/MAX3232-RS232-to-TTL-Serial-Port-Converter-Module-DB9-Connector-MAX232/262241627343
Cheers,
Adam
---==
Adam,
You need to consider what cable you will use, how many devices you need to
feed, and what distance is involved. I've fed a couple of PCs from the same
RS232 device, just the data out and CD (PPS) lines, of course. Not
paralleling the data into the GPS device. One PC is ~4m away, and the two
signals are fed over a twin-pair coaxial cable. Likely a 3-core unscreened
cable would also be OK over such a short distance. The other PC is about a
metre away.
If you're talking about ten PCs I would have a number of TTL to RS232
converters, each feeding 2-3 PCs, or a controlled impedance cable (50 or 75
ohms) with tap-offs along the cable and a termination at the far end. The
old thin-wire Ethernet comes to mind.
But others here have more experience than me, though, and may be able to
recommend surplus units to do the job.
Cheers,
David
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
On Wed, Sep 25, 2019 at 8:01 PM David J Taylor via time-nuts <
time-nuts@lists.febo.com> wrote:
From: Adam Kumiszcza
Hi again!
My raspi is now in a new location. The GPS signal is fine, the window is
not south-facing, but the antenna is outside the window attached to a metal
windowsill, and there are no buildings nearby.
I'm coming back to the idea of distributing PPS signal. Do you think such a
contraption could work?
I mean, stacking it over the uputronics board and soldiering some pins.
The MAX3232 chip is the same as on these kind of devices:
Cheers,
Adam
---==
Adam,
You need to consider what cable you will use, how many devices you need to
feed, and what distance is involved. I've fed a couple of PCs from the
same
RS232 device, just the data out and CD (PPS) lines, of course. Not
paralleling the data into the GPS device. One PC is ~4m away, and the two
signals are fed over a twin-pair coaxial cable. Likely a 3-core
unscreened
cable would also be OK over such a short distance. The other PC is about
a
metre away.
If you're talking about ten PCs I would have a number of TTL to RS232
converters, each feeding 2-3 PCs, or a controlled impedance cable (50 or
75
ohms) with tap-offs along the cable and a termination at the far end. The
old thin-wire Ethernet comes to mind.
But others here have more experience than me, though, and may be able to
recommend surplus units to do the job.
Cheers,
David
It will be connected via a short cable (1,5 m or less) to one computer. The
second will join much later, I will worry about splitting the signal then.
Other computers would be in different rooms, so I would need another time
source.
My question was rather if stacking another board with serial port on it
would be a good idea. I'm thinking of using PPS signal there directly via
GPIO. And maybe NMEA, too.
Cheers,
Adam
From: Adam Kumiszcza
It will be connected via a short cable (1,5 m or less) to one computer. The
second will join much later, I will worry about splitting the signal then.
Other computers would be in different rooms, so I would need another time
source.
My question was rather if stacking another board with serial port on it
would be a good idea. I'm thinking of using PPS signal there directly via
GPIO. And maybe NMEA, too.
Cheers,
Adam
Adam,
You may be unable to stack another board on top, but that depends on the
boards, of course. I would suggest using the network connection between the
computers (with the Internet as a backup) for getting the coarse seconds.
You then need to know what voltage level is required on the second computer
for its serial connections - +/- 12 V or TTL levels. If it's a standard
serial port on the computer, use a RS232-TTL converter just to connect the
PPS line to the DCD pin (1 on a DB9 connector). No need to the TX/RX lines,
just ground and PPS.
I had hoped that someone else on the group who had real-world experience of
distributing PPS might chip in....
Cheers,
David
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv