[time-nuts] Re: GPS failed

[John Sloan via time-nuts]

> I'd like to get some opinions and war stories regarding GPS reliability at 
> high RF level and elevation locations. 

At last count I’ve got ten GPS/GNSS active antennas scattered around the
house (I have a very understanding spousal unit), including one in the
kitchen skylight and one outside. We are currently in a sunspot cycle, and
this summer has been an unusually active season. Several times I’ve seen
one or more of my systems fail, sometimes for a couple of days at a time.

I subscribe to the NOAA Space Weather Prediction Center alert system.

https://www.swpc.noaa.gov/communities/space-weather-enthusiasts

Inevitably about the time I’m thinking about swapping an antenna to see if
it fixes the problem, I get an alert from the SWPC warning about a major
coronal mass ejection event.

I’ve finally learning to check the SWPC web site first before messing with
hardware. I’ve also learned to check the systems before sunrise (I’m an
early riser anyway) and after sunset.

In each case the systems effected came back to working order without my
having to do anything. Some antennas - regardless of location - seem to
be affected more than others.

(Why so many antennas? Five of them are GPS-disciplined NTP servers. Two
of them are part of a little NTP/GPS monitoring system I built. Two are
part of a Differential GNSS test bed I run 24x7. And one is just the test
antenna to my work bench for whatever I’m working on.)

- John

--
J. L. Sloan Digital Aggregates Corporation
+1.303.489.5178 3440 Youngfield Street
mailto:jsl...@diag.com  #209
http://www.diag.com Wheat Ridge CO 80033 USA




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

[John Sloan]

> In this application RPis seem to last for many years - in others where we
> use the SD-card (e.g. influxdb or similar) they seem to regularly fail in
> 1-2 years, requiring an reformat or new SD-card. An RPi or similar with a
> more robust SSD/M2 drive would be good.

I’ve had the same experience with the SD cards.

At least the most recent Raspberry Pis (e.g. the 4B) support firmware to boot 
from USB with just a little configuration effort. I just recently starting 
playing with this, booting a RPi 4B from a USB-attached Samsung T5 SSD. It 
seems to work mostly fine (caveat: see below). For other reasons, I’ve been 
running a RPi-specific version of Linux MATE, but Raspbian should work okay 
too. (I tried the RPi-specific image of Ubuntu, since I run Ubuntu on my Intel 
machines, but was not terribly impressed; slow interactive response.)

One thing I did run into: if I try to plug too many USB devices in along with 
the SSD - e.g. in my case a mouse, keyboard, and GPS dongle - the system 
crashes because the SSD USB connection resets. It seems to be a power problem; 
I solved it with an external powered USB hub, leaving the SSD on a USB port on 
the RPi.

:John

--
J. L. Sloan Digital Aggregates Corporation
+1.303.489.5178 3440 Youngfield Street
mailto:jsl...@diag.com  #209
http://www.diag.com Wheat Ridge CO 80033 USA

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

[John Sloan]

I have four home-built clocks, each using a Raspberry Pi, all with slightly 
different designs, all running gpsd and ntpd (so all are NTP servers on my home 
network). Three are GPS disciplined; one is WWVB disciplined. Two of the GPS 
clocks use the modem-control lines on a serial port for the 1PPS signal, one 
uses the simulated modem-control signals on a USB-connected GPS dongle. One of 
the GPS clocks has a cesium chip-scale atomic clock - specifically, a Jackson 
Labs Technologies dev board with a Microsemi CSAC - for holdover (there’s no 
kill like overkill).

All four clocks use an Adafruit “Pi Plate” LCD board with a two-line display to 
display the date and time.

https://www.adafruit.com/product/1115

The display format could have been anything I chose, but I implemented one that 
looks like this (using a 24-hour time so no AM/PM).

Tue 2021-Dec-07
 06:33:49 MST

They all run the same trivial Python script that I wrote to read the system 
clock (which is disciplined to NTP, and hence to GPS or WWVB time) and drive 
the display. The script runs five times a second. Efficiency is not really an 
issue since this is running on a quad-core processor. An entire core could be 
dedicated to just updating the display. I leave that to the Linux scheduler. 
This approach combines the accuracy of GPS-disciplined time with support for 
time zones and Daylight Saving Time adjustments in the system clock.

The time on the LCD is as accurate as I need it to be, since it’s just a 
human-read display. The NTP time provided by each clock is at least competitive 
with getting the time from NTP servers across the internet. I have another 
Raspberry Pi that uses ntpq to query all of my clocks, along with two 
commercial NTP servers on my network, plus two external servers, and compares 
them. Based on its own measurements, it typically chooses the atomic clock as 
the best reference.

There is undoubtedly a lot of room for improvement in all of this, especially 
in my WWVB clock.

Here is a link of all of my blog articles on clock- and time-related stuff.

https://coverclock.blogspot.com/search/label/Horology

Some of those articles will include links to my GitHub repositories for those 
projects.

Here is an album of photographs of all of my NTP servers, both home-brew and 
commercial.

https://flic.kr/s/aHsmgrizkL

:John

--
J. L. Sloan Digital Aggregates Corporation
+1.303.489.5178 3440 Youngfield Street
mailto:jsl...@diag.com  #209
http://www.diag.com Wheat Ridge CO 80033 USA

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Re: [time-nuts] World's most precise.... wall clock

[John Sloan]

I’ve built several small home-brew NTP servers using a Raspberry Pi,
a GPS receiver, and an LCD display. Most of them are desk clocks.
My favorite one (and the biggest money sink) is a mantle clock in my
living room that incorporates a chip-scale cesium “atomic clock”.

Photo: https://flic.kr/p/2kqoHC7

Blog article: 
https://coverclock.blogspot.com/2017/05/my-stratum-0-atomic-clock_9.html

Git repo: https://github.com/coverclock/com-diag-astrolabe

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 


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[time-nuts] small multi-timezone display

[John Sloan]

I’d investigate whether there was an Android “World Clock” app whose display 
had your requirements, then buy an Android tablet in your price range and with 
the appropriate form factor. (I like the “World Clock” app on my iPhone, but 
I’ve never encountered a cheap iPhone.)

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 

> On Jan 8, 2021, at 8:29 , time-nuts-requ...@lists.febo.com wrote:
> 
> [time-nuts] small multi-timezone display

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Re: [time-nuts] New Member GPS NMEATime Trouble

[John Sloan]

TG9AJR Juan Munoz mailto:tg9...@gmail.com>> writes:
> But I tried the GlobalSat and cause issues with NMEATime that will Not
> Responding and had to End Task. I did unplugged the U-BLOX from the PC and
> put the GlobalSat instead.

I’ve never used any of these devices on Windows - all my GNSS work is under 
Linux - but it’s possible you just need a Windows driver for it.

I’ve not used the U-BLOX UB-6010 specifically, but I’ve used lots of other 
U-Blox devices. I’ve had excellent luck with them. The brand is my so far 
preference for current and future work. I’m guessing just from the model number 
that this is a 6th generation U-Blox device. One of my Linux-based NTP servers 
uses a U-Blox LEA-6T receiver, also a gen 6 device, with the GPS daemon, with 
no issues.

The GlobalSat BU-353-S4 is one of my favorite inexpensive USB-attached GPS 
dongles. From what I’ve been able to tell running these with my own GPS 
software under Linux, it uses a SiRF Star IV GPS receiver with a Prolific 
USB-to-serial interface chip. The serial interface expects to run at 4800 baud, 
8 bits, 1 stop bit, no parity. The GPS stage updates at 1Hz. It enumerates on 
the USB bus as vendor 0x067B product 0x2303, and as a USB (serial) device, 
versus an ACM (modem) device, so no modem control.

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 
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[time-nuts] Hobbyist and prototyping boards with U-blox ZED-F9P

[John Sloan]

Folks:

I’ve been doing a lot of SW work using the U-blox ZED-F9P chip over the past 
few months. Being a SW guy, I try to minimize the amount of breadboarding and 
HW integration I have to do.

For several months most of my work has been using the SimpleRTK2B board from 
Ardusimple in Barcelona Spain: US$193 plus shipping.

https://www.ardusimple.com/simplertk2b/

However, recently I noticed that SparkFun just up the road from me in Boulder 
Colorado has a GPS-RTK2 board with a F9P: $220 plus shipping.

https://www.sparkfun.com/products/15136

The GPS-RTK2 is little more than the SimpleRTK2B, with different additional 
capabilities. Since ultimately all I needed was the USB connection for my SW 
hosted on a Raspberry Pi, the SparkFun board worked with my SW with zero 
changes or drama.

:John

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 
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Re: [time-nuts] NIST time and frequency seminar - 11-14 June in Boulder, CO

[John Sloan]

Here is a write up from when I attended the NIST Time & Frequency Seminar
last year (2018). Coincidentally, I had just had a tour of the NIST T
facilities a month or two before as part of another event. In the
spirit of full disclosure: I’m an embedded software developer who
routinely deals with precision frequency references (e.g. when I wrote
firmware for ATM products) and geolocation (for many different
applications). I like to say “I’m not a hardware engineer, but I keep
a hardware engineer on speed dial”. I got a lot out of the seminar,
but a EE specializing in T would likely get even more.

https://coverclock.blogspot.com/2018/06/wibbley-wobbley-timey-wimey.html

:John Sloan



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Re: [time-nuts] Lost GPS lock or 1PPS recently?

[John Sloan]

Folks:

Well blow me down. It took some Google Maps fu on the web on my part, but
my time and place does indeed coincide with this “GPS Interference Testing” at
White Sands Missile Range. I just happened to be in my home office watching
several of my GPS-disciplined NTP servers when this occurred. Thanks, Graham!

:John

> ZDV   DENVER (ARTCC),CO. [Back to Top] !GPS 08/260 (KZDV A0287/18) ZDV NAV
> GPS (WSMR GPS 18-20) (INCLUDING WAAS, GBAS, AND ADS-B) MAY NOT BE AVBL WI A
> 359NM RADIUS CENTERED AT 45N1063840W (TCS054036) FL400-UNL, 311NM
> RADIUS AT FL250, 215NM RADIUS AT 1FT, 223NM RADIUS AT 4000FT AGL, 169NM
> RADIUS AT 50FT AGL DLY 1830-2230 1809031830-1809082230

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 


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[time-nuts] Lost GPS lock or 1PPS recently?

[John Sloan]

Folks:

GPS jamming and spoofing isn't really my area of expertise, but it's something 
I worry about, not just for its impact on geolocation and navigation 
applications, but also because GPS has become critical as a high precision 
timing reference in the telecommunications realm, which *is* my area of 
expertise.

Yesterday (2018-09-03) afternoon (about 22:00UTC, 16:00MDT) I noticed one of my 
three home-made GPS-disciplined NTP servers had lost its GPS lock. After some 
forensics on my part, this (2018-09-04) morning (about 16:00UTC, 10:00MDT) I 
replaced the amplified antenna, and the device reacquired its lock. I figured 
it was just an antenna failures; this is an amplified filtered antenna so it 
has active electronics.

Then just an hour or so later, I noticed one of my commercial GPS-disciplined 
NTP servers (TimeMachines) had lost the GPS 1PPS timing signal, but indicated 
it still had GPS lock. (I question now what this actually means in the context 
of this particular device). As a troubleshooting step, I power cycled the 
device, and it reacquired 1PPS. But as I did that, the second commercial 
GPS-disciplined NTP server (Uputronics) right next to it lit up with a red 
warning on its display, indicating it had lost GPS lock. A minute or so later 
it also reacquired lock and indicated 1PPS, with no action on my part.

All of these devices are completely independent, have different software (and 
probably hardware), have separate amplified antennas sitting side by side in 
the window of my home office, and are not all on the same electrical outlet 
(but may be on the same household circuit).

I lit up the LCD display on my little GPS monitoring tool I built that runs 
Lady Heather 24x7 and see on the graphical display sudden jumps of reduced 
timing accuracy of a factor of 10^2 (from nanoseconds to hundreds of 
nanoseconds) in the recent past. But I’m thinking this can also be caused just 
by the dynamic satellite geometry, and might be normal. It’s not like I watch 
this graph all the time (even though it does sit right in front of me on my 
desk).

No clue what's going on in my suburb near Golden Colorado. But I’m a little 
freaked out. Trying to figure out which rule, [1] It’s something stupid I’ve 
done, or [2] I am not unique, to apply.

:John

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 
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[time-nuts] NIST Tour and Time & Frequency Seminar

[John Sloan]

This summer, somewhat coincidentally, I got to take a tour of some of the NIST 
Time and Frequency Division, rode my motorcycle up to Fort Collins to see the 
WWVB antennas, and attended the NIST 43rd Annual Time & Frequency Seminar. I 
wrote a couple of blog articles with my notes and photographs. Could be someone 
here will find these interesting.

https://coverclock.blogspot.com/2018/05/time-is-precious.html

https://coverclock.blogspot.com/2018/06/wibbley-wobbley-timey-wimey.html

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 
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