[time-nuts] Re: Suggestions solicited for Pi/GPSDO ntp server

[David Taylor via time-nuts]

On 26/05/2022 17:44, Lee Reynolds via time-nuts wrote:

Hi, Lords of Time!

(Been a lurker for many years, just know too little to add but am always
fascinated by your discussions. It almost reads like theological
discursions at some points, it gets into such fine and abstruse points!)

I think it's about time to retire my old former cell site GPSDO.

Technology has improved and I'm thinking of setting up a Raspberry Pi
based ntp server for the local devices. (I also have some spare Pi's, so...)

Does anyone have any suggestions for a good solid Pi/GPSDO setup and
code for such a purpose? Something like Leo's device but, of course,
much cheaper?

Any suggestions would be greatly appreciated.

TIA,

    Lee


Lee,

What accuracy are you wanting for your "local devices"?  A Windows box NTP 
server could give you hundreds of microseconds, a Raspberry Pi tens of 
microseconds.  With the RPi you could have several local GPS/PPS/NTP servers 
perhaps located in different parts of the building.


Hal has given some good advice.  I particularly sympathise with the "out of 
date" part, where Linux OS changes almost on the basis of (it sometime seems) 
"if it works, break it!".  I've built a few of the Raspberry Pi NTP servers, 
and in practice the Ethernet being over USB isn't an issue, but if you can get 
a Pi 4 that would reduce that problem.


But the Pi4 isn't so easily obtainable right now, and it generates rather more 
heat, so the stability of the CPU clock isn't as good as on earlier RPi models. 
 Ambient temperature can be a problem, so try to keep the RPi out of direct 
sunshine, preferably in a cupboard away from any heating.  All to keep the CPU 
clock stable!  No need for a display, it can all be built from the command line 
over SSH.


Ask if you have further questions.

David
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[time-nuts] Re: GPScon peogram

[David Taylor via time-nuts]

On 06/04/2022 00:33, Lon Cottingham wrote:

      How does one acquire GPScon?  The only source I find in from Jackson's 
Labs ant it only works with Jackson Lab's products. 73 de Lon, K5JV


I suppose it isn't this program:

  http://www.realhamradio.com/gpscon-info.htm

What about ublox U-Center or Lady Heather?

David
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[time-nuts] Re: GPSDO - GPS1300-10-1000 by RFX Ltd. UK

[David Taylor via time-nuts]

On 02/03/2022 17:34, va2...@ebox.net wrote:

Hello to all members.

I want to add to my lab a Pi based display that would show a GNSS SV map
like the one attached to this message.

Any suggestions ?

Thank you !

Claude VA2 HDD


Claude,

I would look into gpsd.  I guess someone will have made a graphical add-on, if 
not a text simulation of a graphical display.  Mine was u-blox u-center with a 
serial line actually from an RPi HAT, operated stand-alone.


73,
David GM8ARV
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[time-nuts] Re: GPSDO - GPS1300-10-1000 by RFX Ltd. UK

[David Taylor via time-nuts]

On 01/03/2022 22:43, Bob kb8tq wrote:

Assuming you are south of Hadrian’s Wall, you will have GPS sats overhead
at least occasionally. The bulk of what you will be able to “see” will be to the
south. If you really have a good antenna location and are a bit north, you may
be able to “see” sats on the other side of the north pole. More or less, there
is a big coverage blank area over the poles with GPS.


Even north of Hadrian's wall we get GNSS satellites overhead.  Here's with an 
indoor antenna dual-band setup.  None reach 40 dB.


David
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[time-nuts] Re: electronics question or how not to fry my raspberry pi

[David Taylor via time-nuts]

On 28/01/2022 19:41, folkert wrote:

Hi,

[]

The RPI doesn't like 5v on its GPIO pins.
So I wonder:
- can I feed the picdiv 5v on its GPIO pin while giving it a 3.3v
   voltage so that it outputs 3.3v as well to the rpi pins?
- or should I use a voltage divider? I was thinking of a 4.7k ohm and
   8.2k ohm resistor giving slightly less than 3.2v - will that work? or
   will that attenuate the signal too much? The 50 ohm bnc cable between
   the amplifier and the rpi is 3m long. Anything else I should be aware
   of?


Regards,

Folkert van Heusden
PD9FVH


Folkert,

In similar circumstances I've used a resistive divider and it's worked exactly 
as expected.


For such short cables there are unlikely to be any other effects you need to 
take care of.  You might like to see what the voltage levels are if you 
terminate the 50-ohm cable with a 47-ohm resistor - it /may/ drop to 2.5V 
peak-to-peak.


I would simply try it and see.

Of course, if the idea is to send PPS to the RPi getting the appropriate GPS 
devices would be my preferred solution!


Oh, just looked, I would expect to see a square-wave, not the near sine-wave 
your 'scope trace shows.  Is it nearer to square with a much faster timebase?


Cheers,
David
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[time-nuts] Re: Derivation of time from celestial sight

[David Taylor via time-nuts]

On 27/12/2021 20:18, Brent wrote:

My understanding (and I could be wrong) is that one could derive 'stellar'
time from a start sight/fix on polaris or another well tracked celestial
object.  I was once told that early editions of Bowditch provided the
process (for the moon I was told) although one of the relatively old
edition's that I have doesn't provide it.


My previous answer mentioned precision, of course, not accuracy.  And the error 
I mentioned was not the error in GPS which places the zero degree meridian some 
102m east of Greenwich!


David
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[time-nuts] Re: Derivation of time from celestial sight

[David Taylor via time-nuts]

On 27/12/2021 20:18, Brent wrote:

My understanding (and I could be wrong) is that one could derive 'stellar'
time from a start sight/fix on polaris or another well tracked celestial
object.  I was once told that early editions of Bowditch provided the
process (for the moon I was told) although one of the relatively old
edition's that I have doesn't provide it.

Some theodolite manufacturers provided attachments to aid the process (for
the high zenith where a theodolite experiences reduced accuracy), and those
attachments were dated and calibrated for their year of manufacture and
came with tables for use in future years.

That's about all I know or can find on the subject.  Can anyone here point
me to any published literature?  Anyone have experience trying?  Any idea
what type of accuracy can be expected?

Got some new toys coming and need something to do with them

Brent


Brent,

You might find something like these of interest:

  http://www.thegreenwichmeridian.org/tgm/articles.php?article=6

  https://www.rmg.co.uk/stories/topics/airys-transit-circle-dawn-universal-day

  http://www.royalobservatorygreenwich.org/articles.php?article=1087

There is a possibly apocryphal tale that some students at Cambridge did this in 
the late '60s or early '70s and getting about a second or two accuracy, and 
discovering that the longitude of the Cambridge Observatory was some hundred 
metres out.  You might find a reference, and I might be mistaken!


Cheers,
David
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[time-nuts] Re: Poor's man NTP

[David Taylor via time-nuts]

On 18/12/2021 21:13, giuse...@marullo.it wrote:

Hi Bob,

If you have a requirement for always being in the microseconds rather than 
milliseconds, PTP is a better approach.

I just need it for logs and computer time sync, PTP seems overkill for my 
requirements.
It is a small lab, then maybe I could offer NTP (SecureNTP) service for the 
rest of the company, if I will add other NTP/SecureNTP servers depending on the 
load.

Giuseppe Marullo
IW2JWW - JN45RQ


Giuseppe,

If you are considering something for "the rest of the company" you could save 
yourself a lot of bother by getting something like the LeoNTP box:


  http://www.leobodnar.com/shop/index.php?main_page=product_info_id=272

  https://store.uputronics.com/index.php?route=product/category=70

It just sits there and works, and can serve many thousands of NTP clients. 
Good luck in finding one, though, due to the current component shortage.


73,
David GM8ARV
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[time-nuts] Re: Poor's man NTP

[David Taylor via time-nuts]

On 16/12/2021 23:37, giuse...@marullo.it wrote:

Hi,

just wondering if a PI4 could be a suitable NTP server for a small lab (and
maybe with some other NTP servers for my company, about 2000 clients).

Main use is for correct timestamp on logs/computer time sync.

I setup the NTP using Adafruit Ultimate GPS shield(with battery), and the
GPS/GLONASS Antenna(cheap one, not a timing antenna). Antenna is on a roof
window with a small metal base, outside.

What is the accuracy I could expect from it?


You can see the offsets reported by a number of Raspberry Pi NTP servers here:

  https://www.satsignal.eu/mrtg/performance_ntp.php

As a very rough guide I would expect a PPS-based RPi to be within 100 us 
easily, and perhaps considerably better (~10 us) in a constant temperature 
environment, and with no other load.  I don't know about load capacity as I've 
not tested that, but here it's serving perhaps 50 devices.  With classic NTP 
which is what I use there will be a period before the offset becomes near-zero 
so 24 x 7 is the way to operate.


Although there are some devices on that page with LAN, 2.4 GHz or 5 GHz 
connections, for beat accuracy you must use the PPS signal from the GPS as you 
know.  The "o" tally code suggests that's OK.


I suggest using the "pool" directive rather than multiple pool servers:

  https://www.satsignal.eu/ntp/setup.html#pool

Cheers,
David
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[time-nuts] Re: PPS latency? User vs kernel mode

[David Taylor via time-nuts]

On 13/12/2021 21:22, Trent Piepho wrote:

And finally we can have the kernel act on the PPS timestamps itself.
But NTP network traffic might be a bridge too far.  Mills describes
this as a "hardpps()".  This was added to Linux in 2011 by Alexander
Gordeev, based on Mills' work, but with a different implementation.
This is a "kernel consumer" of PPS timestamps, which can be used to
steer the PLL entirely inside kernel code.  It's enabled with the
kernel config option NTP_PPS.  One can easily see if this is present
in the kernel via the usual methods.  It is often NOT enabled because
it doesn't work with tickless kernels.  I do now know if current ntpd
supports this or what it takes to use it with ntpd.  I have used it,
but I wrote my own code from scratch to integrate it with a GPS module
to perform time sync without installing either ntpd nor chrony.


Trent,

Thanks for that!  I was only aware of a limited subset of that as I came later 
to NTP on Linux (it was mostly Windows before), and I understood even less at 
the time!  Your notes helped clarify things, thanks.


David
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[time-nuts] Re: PPS latency? User vs kernel mode

[David Taylor via time-nuts]

On 13/12/2021 04:17, Adam Space wrote:

What do you mean by "kernel mode"?

I am referring to this guide
  that another user here
recommended to me a bit ago. I am not too sure myself since I am relatively
new to this.


That document is now historic background.

It refers to the early "kernel mode" when (AIUI) part of the OS rather than NTP 
did the fine clock adjustment.  I recall that early Raspberry PI OS kernels did 
not include all the functions required for the most accurate timekeeping, and 
that a kernel recompile was required.


Fortunately that is no longer required, and recent OS versions can directly 
accept PPS pulses, although they no longer include NTP!


You may find my current version less confusing:

  https://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html

although the confusion is now within the different RPi models, mapping the 
different physical serial ports to the virtual ports, and choosing the ports 
which don't have a variable clock speed!


In Windows we do need to distinguish user/kernel modes, because we used to have 
kernel mode as a modification of the device driver but it's no longer 
accessible, and a workaround runs in user space, hence user mode.


Cheers,
David
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[time-nuts] Re: Clock display on Linux systems?

[David Taylor via time-nuts]

On 05/12/2021 20:53, Adam Space wrote:

Most distributions of Linux already have a "clock" application that shows
the system time, but I am wondering how to program a more customizable
display on a Linux system / Raspberry pi. There are a few solutions that
pop up by googling the issue, but these are all insufficient. For example,
the only solutions in Python (which I would prefer to use if possible, but
not necessary) I have found are 1) using a library like pygame or tkinter
to build a display or 2) doing something more barebones like displaying the
time and sleep() ing for a second. 1) is terribly inefficient for a display
of accurate time, because either you have a refresh rate that is low and
the clock updates with significant lag, or you have a high refresh rate
which eats up large processing power. 2) is also inefficient because the
frequency of a local clock may be poor, so long term accuracy can only be
sustained with synchronization via NTP for example.

Perhaps there are lower level Linux commands that could be used for this?
I'm not sure. Any suggestions are welcome.

Adam


Adam,

I have a simple digital wall clock program for the Raspberry Pi if it's of any 
help.  FreePascal/Lazarus both source and executable available:


  https://www.satsignal.eu/raspberry-pi/DigitalClock.html

Cheers,
David
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[time-nuts] Re: Leap indicator set to 1 !

[David Taylor via time-nuts]

On 27/11/2021 15:22, Steven Sommars wrote:

FYI.

At 2021-11-27 00:00:00 UTC many public NTP servers began setting the leap
indicator to 1.
This may be gpsd related



Yes, I see it on [possibly] one of my ISP's servers:

   cpc137586-lock4-2-0-cust263.6-1.cable.virginm.net
   86.3.245.8

I wrote a little (Windows) program to check this.

Cheers,
David
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[time-nuts] Re: List Opinion/Suggestion(s)

[David Taylor via time-nuts]

On 25/11/2021 08:14, Hal Murray wrote:



(according to a pre-configured  compile-time constant),


Have you looked at the tinker stuff in the config file?  I'd expect it to be
there.


I don't see it in there, Hal.

David
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[time-nuts] Re: List Opinion/Suggestion(s)

[David Taylor via time-nuts]

kb...@n1k.org  said:

I would strongly suggest that with NTP ???more is better???. Three reference
devices is about the minimum. Five is a good target to aim for.


One suggestion I make to folk who ask is to use the "pool" directive.  This 
allows NTP to choose as many servers as it needs (according to a pre-configured 
compile-time constant), and it will automatically drop and add servers as 
needed.  OK, it's a little more complicated than that but using pool is easy:


Replace the lines:

# Use pool NTP servers
server 0.uk.pool.ntp.org  iburst
server 1.uk.pool.ntp.org  iburst
server 2.uk.pool.ntp.org  iburst

with the single line:

# Use pool NTP servers
pool uk.pool.ntp.org  iburst

if you are in the US, for example:

# Use pool NTP servers
pool us.pool.ntp.org  iburst

and you can use multiple lines such as a Dutch user might have:

# Use pool NTP servers
pool nl.pool.ntp.org  iburst
pool uk.pool.ntp.org  iburst

See:
  https://www.satsignal.eu/ntp/setup.html#pool

Cheers,
David
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[time-nuts] Re: NTP servers

[David Taylor via time-nuts]

On 22/11/2021 02:29, McFail Troll wrote:

Hi all, I am new to the mailing list, and pretty new to timing stuff in
general. I wanted to ask if any of you folks who have a more advanced
set-up (synchronization via gps/radio, or just a well working rubidium
clock or something) maintain a solid stratum 1 NTP server. Of course, I am
aware that there are plenty of good stratum 1 NTP servers open to the
public (e.g. NIST's servers), but I am curious to see if I could sync up
with some of you guys who seem to have some pretty cool set-ups.

Btw, sorry if this has been asked before on this list. Thanks


You may find some helpful information on my Web page:

  https://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html

about using a GPS/PPS device with a Raspberry Pi.  This gets you down into the 
microsecond region at a low cost and a low power consumption - helpful as 
leaving the device on 24x7 is best.


Be aware that many of the public stratum-1 servers are overloaded and perhaps 
not as good as you might want.


Cheers,
David
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[time-nuts] Re: in-ground clock room

[David Taylor via time-nuts]

On 09/09/2021 03:36, Bill Beam wrote:

Tom,

How long do you expect your proposed voult to go undisturbed?
I have several pendulum clocks.  They are disturbed every couple of months
by earth quakes.  By disturbed, I mean pendulum banging against the case 
walls
Any ground motion that can be felt will upset the clocks.  Often the clocks will
signal an earth quake that is not felt.

Good luck.

Bill Beam
NL7F


Bill,

It sounds as if you live in an area where monitoring of earthquakes would be of 
interest!  If you haven't got something already, you might like to look at the 
Raspberry Shake:


  https://raspberryshake.org/

The devices are not at the professional seismograph level.  They operate a 
world-wide network.


73,
David GM8ARV
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[time-nuts] Re: Comparison/evaluation of u-blox timing receivers

[David Taylor via time-nuts]

On 24/08/2021 02:51, John Ackermann N8UR wrote:

In 2020 I did an extensive evaluation of the timing ability of the
u-blox LEA-M8F, NEO-M8N, NEO-M8T, NEO-M9N, ZED-F9P, and ZED-F9T.  The
work was made possible by support from the HamSci consortium
(https://hamsci.org) under NSF grants supporting HamSci activities.

I was sure I'd posted about the paper on time-nuts, but I can't find any
record that I did, so this is a belated announcement.  It's available
for download from

https://hamsci.org/sites/default/files/publications/2020_TAPR_DCC/N8UR_GPS_Evaluation_August2020.pdf

As BobC says, "Lots of fun!"

John


Most interesting, John, thanks for posting.

(Accidentally send directly, sorry.)

David GM8ARV
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[time-nuts] Re: GPS antenna distribution?

[David Taylor via time-nuts]

On 28/06/2021 21:56, lstosk...@cox.net wrote:

Thanks guys.  Opened a lot of things to think of.  Makes me wonder how I get 
any results from a north facing window with the UV coating!  Will work out 
something.  N0UU


Maybe an antenna in the loft might produce better results?  Check it 
with your (Android) phone/tablet which can display the signal strengths.


You could consider using something which sticks to the outside of the 
window if the attenuation is too great?  Cable through a small hole, or 
where the window opens?


73,
David GM8ARV
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[time-nuts] Raspberry Pi GPS/PPS/RTC HAT

[David Taylor via time-nuts]

For UK (and perhaps European) enthusiasts, if the import duty, VAT and 
collection fee is too great, you might like to look at:



https://store.uputronics.com/index.php?route=product/product=60_64_id=81

I hope this is OK to post, but since Brexit buying anything from outside 
the UK is a lottery as to what the final price may be.


Cheers,
David
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Re: [time-nuts] U-blox F9T performance (was: U-blox teaser)

[David Taylor via time-nuts]

On 01/03/2021 00:52, Thomas Abbott wrote:

Hello Time Nuts, first post from a long-time lurker.

In late 2019 I evaluated the Ublox F9T for a project. Here is a graph of
the time difference between PPS outputs of two RCB-F9T boards on the bench.
Each had a U-blox dual-band ANN-MB-01-00 antenna, they were 1 metre apart,
on ground planes, with excellent sky view.

[]

Thomas

Any chance of adding X and Y scales to the graphs?

David
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Re: [time-nuts] Raspberry Pi 4 oscillator replacement

[David Taylor via time-nuts]

On 04/02/2021 10:20, Avamander wrote:

Hi,

I was wondering if anyone here has replaced the 54 MHz oscillator on the
Raspberry Pi 4 with a GNSS-disciplined rubidium standard? An overkill
upgrade, but is technically doable? What hardware would it take in addition
to a GNSS-disciplined rubidium standard and a Pi 4?

Here's where I got my inspiration from, someone replacing the oscillator on
a Pi 3 with a TXCO:
https://raspberrypi.stackexchange.com/questions/74482/switch-out-the-x1-oscillator-on-a-rpi-2-3


Yours sincerely,
Avamander


I would likely use one of these:


http://www.leobodnar.com/shop/index.php?main_page=product_info_id=301

Cheers,
David
--
SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv

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