[time-nuts] Need Time Help
kb8tq at n1k.org
Tue Oct 4 08:03:08 EDT 2016
As others have mentioned, you have two strikes against you:
1) Modern laptops *love* power saving. That makes them poor time keepers
at the millisecond level. It takes some well thought out software in the OS to
keep track of all the strange things they do.
2) Windows XP is getting a bit old and tired. It’s internals were done long ago
on hardware very different than what we have today. It has a lot of limitations.
Between the two, you will always struggle. An RTOS would do much better than
XP for timing. Virtually all of the more modern OS’s (some of them free) will
handle timing better than XP does. That’s not to say the laptop will not ultimately
limit what you can do.
There are a few more strikes when you try do do NTP over a residential internet
connection. Cable modems and the like are not designed for high accuracy
By far the best solution is to get timing from a GPS. Even a cheap on, running over
a lousy cable will get you into the 1 us region if it’s a modern unit. That is way
better than the 5 ms that you are after. Moving it around on a local LAN with
good cabling isn’t going to degrade it by much over 1 ms, even using NTP.
One alternative to the whole “computers are a mess” issue is to simply put the
GPS into the same hardware that is receiving / transmitting the signals . There
are a *lot* of GPS modules on the market that will put out an accurate PPS signal.
Depending on how picky you are, they are in the $10 to $50 range. Let the local
hardware do the job rather than network the whole thing. Local hardware running
a reasonable OS is in the $30 to $100 range, again depending on features. Given
that you probably already have the price of a small car tied up in antenna systems,
this isn’t that crazy a cost.
> On Oct 4, 2016, at 12:41 AM, Larry Hower <hower at hower.net> wrote:
> Hello to the List:
> 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.
> We are hoping to achieve less than 5ms deviation, although anything below
> 15ms will be adequate for now.
> 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.
> We are using WSJT-X software. We use standard receivers plus we have tried
> a few SDRs.
> Sorry for the oversimplified example but I want to make sure we are all on
> the same page.
> As background:
> 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.
> 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
> *Standard Receivers*
> ICOMs (910/9100 and others – non-SDR). Locked to 10MHz external osc
> reference. We have frequency accuracy of 1 to 2 Hertz at 10GHz.
> 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.
> *Some time related hardware details*
> *1. Global Star 4 USB and Serial Connections*
> 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.
> *2. TimeNet NTP Device*
> 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.
> The G Star units have been installed at 2 separate locations, tested using
> WSJT-X QRA 64 and WSPR-2 signals on 10.137MHz.
> Similar tests with a TimeNet unit at one end and G Stars at the other end.
> G Star units were installed on the XP laptops with the PPS option enabled
> and running WSJT-X. These XP units seem to have their time “in sync”. See
> 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.
> *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
> *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.
> 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.
> I ask for advice on how we can use the above gear or other gear or other
> software to have our setup deliver better than 15ms accuracy.
> Ultimately we want sub-millisecond accuracy.
> Any help will be very much appreciated. Thanks in advance for anything you
> can advise.
> Larry Hower
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