[time-nuts] Re: NTP server replacement GPS receiver

[Fleeson, Richard]

Yes you are correct Heols has been very responsive and helpful as have others I have contacted like Furuno, Jackson Engineering and Symmetricom.  So far the Heols module is the only one I have tried that works in the S200.  I sent a full description of my S350 issues to Heols at the same time I reached out to the Time-Nuts brain trust.   My search is an effort for work to avoid the cost of new replacement NTP servers.  I have limited time so the sub-module solution and a software update is what I am looking for.

Talking to Furuno the GT-8031 will produce the correct date.  It just takes setting the date/time registers in the GT-8031.  This needs to be done at boot up or after a Pin 6 reset.  The date/time setting should hold if you put a battery feed on Pin 7.  For those who might score a used Symmetricom for their home basement lab I think there may be a cheap "Man In The Middle" way to hack the original Symmetricom sub module.  I have not tried this but you could intercept the serial commands sent to Furuno GT-8031 and set the correct date and time registers as well as if needed truncate the week roll over output back to the Symmetricom.   Of course you would need to allow the other normal Symmetricom/GT-8031 TX/RX data flow as well.

This is the GT-8031 pinout for TX/RX and Battery connections:
[cid:image001.png at 01D962FF.82BD8020]

Let me know if anyone needs the protocol for the GT-8031.

Richard

From: Steven Sommars <stevesommarsntp at gmail.com>
Sent: Wednesday, March 29, 2023 8:15 PM
To: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Cc: nlsa at nlsa.com; Fleeson, Richard <RFLEESON at c-span.org>
Subject: Re: [time-nuts] Re: NTP server replacement GPS receiver


** WARNING EXTERNAL EMAIL **
Heol Design has been responsive to my support questions, even though I am not a customer (just an observer).

I've seen two issues:  #1  Off by 1 second for a one second duration every hour, beginning XX:59:01     I'm told this is due to software version mismatch.
I'm aware of only one public NTP server with this problem; that site is unable to make the needed software change.
#2   Off by one second for a duration of one hour at the beginning of specific GPS weeks.  I observed this  2023-03-12 00:00 and reported to Heol.
Heol Design told me that the problem comes from the way Tymserve-Datum attempted to avoid GPS WNRO (using leap seconds) and that the problem is expected to recur every 70 or 71 weeks.
I was able to verify this from my historical NTP logs.   They're working on a fix.

Versions do matter.  Check with Heol Design for the required software versions and updates.




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