[time-nuts] Need Time Help

Tue Oct 4 08:51:44 UTC 2016

On 10/4/2016 6:41 AM, Larry Hower wrote:
> Hello to the List:

Hi and welcome!

> After a long and bitter struggle with XP and WIN 10, I am writing to ask
> for some help in solving some problems we have been having in our attempt
> to establish a very accurate time reference for use in EME activities.

You have a much higher budget for amateur radio gear than I do if you're
doing EME. I'm envious. :)

> We are hoping to achieve less than 5ms deviation, although anything below
> 15ms will be adequate for now.

This should be quite feasible, even with Windows.

That said, is such precision really necessary? I know that JT65 and JT9
both require "good" time sync, but is millisecond-level precision
needed? I've had good results for terrestrial contacts with time
differences ranging from 0.0 to 1.0 seconds. EME might require tighter
sync, of course.

> Specifically, we want to use a universal reference that will enable amateur
> radio operators in different parts of the world to start and stop their
> transmissions within a few milliseconds of a specific time. For example, I
> transmit at 12:00:00 for 1.75 minutes and “Joe” listens. Then “Joe”
> transmits at 12:02:00 for 1.75 minutes. Repeat until QSO happens.

GPS should be that "universal" (really, planetary) reference.

> 1. We are using desktops and laptops in separate locations running XP or
> Win 10.
> 
> 2. We have used MS clock tools, including use of Boulder time servers,
> tried both host name and IP address, without reaching the goal.

No surprise. The built in Microsoft timekeeping software is "good
enough" for typical computing purposes (within a second or two) but
isn't really sufficient for your purposes.

Desktops will be easy, assuming they have a serial port or a serial
header on the computer itself. If the desktop only has a serial header,
a cheap adapter like
<https://www.amazon.com/StarTech-com-Serial-Motherboard-Header-PLATE9M16/dp/B001Y1F0HW/>
will connect the header to a standard serial connector.

Laptops might be harder. Using NTP software to a good NTP server on the
internet should get you within a few milliseconds. Synced to a good NTP
server on the LAN with the server using GPS+PPS should get you within a
millisecond.

> 3. We have set up some Serial GPS units with PPS and some USB GPS receivers
> (no PPS) and can get to about 0.2 sec but it is not trusted or close enough.
> 
> 4. We have set up a network time server with similar results.
> 
> 5. Deviation is measured using WSJT-X

> We believe that SDR processing can insert a delay of varying length,
> depending on the software, bandwidth, etc. Our SDR tests seem to have a
> delay of as much as 0.5 sec. And with sometimes variable results. We will
> see how SDRs can be used after we resolve the current issues.

This isn't really surprising. If the SDRs are connected via USB, there's
additional delays and jitter inherent in that connection.

> *Some time related hardware details*
> 
> *1. Global Star 4 USB and Serial Connections*
> 
> http://usglobalsat.com/p-688-bu-353-s4.aspx#images/product/large/688.jpg
> 
> We have 4 of these. Two are older models with serial connections. We have
> serial ports on some computers (XP and a new high-end laptop running WIN
> 10) so we are able to activate the PPS option. Two of the GStar are newer
> models with USB connections which are not able to use the PPS option.
> 
> We have tried NEMATime and NEMATime 2 software on this hardware without
> reaching our goal of <15ms. Range of deviation is from 0.0 to about 0.3
> sec. Drifts.  Deviation is measured using WSJT-X.

The BU-353-S4 lacks a PPS line to precisely signal the start of each
second. (At least the specific one I have for mapping doesn't have that
option.) Although you may get somewhat better precision using the SiRF
binary stream, your deviation is about what I'd expect for a USB
receiver with NMEA output.

Simply put, without PPS you probably won't get closer than 250ms unless
you're quite lucky. Doubly so if you're using PPS-over-USB.

> *2. TimeNet NTP Device*
> 
> http://www.veracityglobal.com/products/networked-video-integ
> ration-devices/timenet.aspx
> 
> We have one of these TimNet units and it has been set up at 2 different
> locations on differing computers according to user instructions. We are
> using the TimNet software as DL'd recently from their web site. We get GPS
> “lock” and Time “lock” shown in the user panel but we do not have faith
> that this is carried into the system clock. Occasionally the "lock"
> indicators go blank but the time seems to be updated when the software is
> strted again (the updated is operation is show at the correct time.  We
> think the app needs some work. Deviation is measured using WSJT-X.  See
> later details.

I wonder if you'll get better results using Meinberg's Windows port of
NTPd: <https://www.meinbergglobal.com/english/sw/ntp.htm> -- you should
be able to configure it to query your TimNet device and get reasonably
good precision.

Meinberg's NTP software is explicitly recommended in the WSJT-X
documentation.

> *WSJT-X*
> 
> We are not sure what, if any, internal delays there are attributable to
> this software. We have been using the same version/build at both ends for
> the tests. The software displays in 0.1 sec increments but will show 0.0sec
> when things appear to be working well. We do not know the actual level of
> precision of the WSJT-X software time measurements. I undersand that WSJT-X
> “reads” the system clock at the start of a period (TX or RX) and displays
> what it finds as the time deviation from the local system clock.

According to the manual at
<http://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main-1.6.0.html#TUT_EX2>,
the DT column shows the offset between the time of the remote station
and your local system clock, not between your local system clock and UTC.

I'm not sure if the time difference displayed compensates for speed of
light delays.

I suspect the software is able to compensate for internal delays, else
it wouldn't be much use.

> *WIN XP*
> 
> There are 2 laptops running XP. They seem to match each other re time using
> WSJT-X, both are “out” usually by less than 0.1ms or 0.2ms. We are fairly
> sure that they are working properly but they need to be more accurate
> (<15ms).

I assume your "out" time is in seconds, not milliseconds.

> *WIN 10*
> 
> Installed on a number of desktop and laptop computers. Many efforts were
> made to make these system clocks reference the GPS devices.
> 
> We became aware that the WIN Time/Date GUI was not always driving the
> setting down into the system clock. We became aware also that the Registry
> entries needed to be confirmed as far as NTP or local reference and the
> sync cycle needed definition because of the same unreliable GUI actions.
> 
> We found that we needed to start the Time Services and deal with some other
> factors.  We have found that in WIN 10 the time/date clock does not show
> the update when it happens automatically according to the setting in the
> directly.  It does how the correct time of sync when we do it manually or
> restart the GUI.
> 
> The end result is that we don't trust WIN 10 and and we are not sure how to
> fix the problem. Linux not allowed for now.
> 
> 
> *Status*
> 
> Our conclusion is that the external gear should be able to provide a more
> accurate reference than we are able to obtain presently.  We think "it is
> in there somewhere" but we can't get it out.
> 
> We have a feeling that the WIN system clocks are not being updated
> correctly or at least in a repeatable manner.  We don't know if the problem
> is hardwaare or software or our setup / configurations.

Try Meinberg's NTP software and GPS receivers with PPS outputs.

I've had good luck with the Garmin GPS 18x LVC
<https://buy.garmin.com/en-US/US/oem/sensors-and-boards/gps-18x-oem/prod27594.html>.
It's available for ~$70 USD from Amazon at
<https://www.amazon.com/Garmin-18x-LVC-Navigator-Unit/dp/B0016O3T7A/> --
it comes with a bare wire connector and you'd need to solder the
appropriate connector for 5V power and serial connections.

Note: you need the LVC model, as this has PPS output. The USB and "PC"
(standard serial) do not do PPS output.

I added some extra bits to blink an LED with each PPS, and an LED for
power. The USB pigtail provides power while the serial connection goes
directly into a hardware serial port. Here's a pictures of my connector:
<http://imgur.com/a/PEiBU>

There's lots of other great GPS receivers with PPS output, including old
timing receivers like the Motorola Oncore, Trimble Resolution T, etc.
Those PPS outputs are typically within 20-100 nanoseconds. Oncore UT+'s
are about $20 on eBay --
<http://www.ebay.com/itm/Motorola-UT-Plus-Oncore-Timing-GPS-1PPS-50-ns-/270467197172>,
while the Resolution T is about $50
<http://www.ebay.com/itm/Trimble-Resolution-T-Timing-GPS-module-12ns-1pps-/252474351979>.
The only downside of the Resolution T is the pinout does not use the
common 2.54mm/0.1" spacing, but instead uses 2mm spacing.

I've had excellent luck with my GPS 18x LVC feeding my Windows 7 PC
running ToyNTP via a hardware serial port:
<http://www.dxatlas.com/ToyNtp/>. It steers the system clock using a
Kalman filter and is remarkably good. I typically see offsets <10
microseconds. The only caveat is that ToyNTP requires NMEA output at
4800bps. Other speeds and other formats won't work; keep this in mind if
you use older GPS receivers that might not output NMEA.

Cheers!
-Pete