[time-nuts] Re: Samsung-Symmetricom GPSDO Rollover Problem

[Bob Camp]

Hi

NMEA is a very basic protocol. You put ASCII “text” commands and get back “text” as a response. If you are doing it on a serial port, you can type the commands and read the results. It does not include the information typically needed to “do a GPSDO”.

The folks who came up with NMEA realized that it would never be able to cover 100% of what people needed to do. They allowed proprietary extensions to the protocol. They are still serial commands and they go in the same way as any other NMEA request. They simply are not part of the default command set. 

In addition, the basic NMEA protocol has been extended a couple of times to cover various new features. Various GNSS systems have been added since NMEA first came out. They now are covered in modern versions of the protocol. In some cases these changes confuse older firmware. 

Binary protocols are very different than NMEA and they are a whole world onto themselves. 

Matching up what this or that firmware “needs” typically is a matter of dealing with a handful of queries and responses. Working out exactly *what* those are for a specific version of firmware is a non-trivial task. Very minor things can and do create very random seeming problems. 

Bob

> On Nov 11, 2024, at 2:05 AM, Brett Fanoga via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Thank you.  I did confirm that the Furuno GPS receiver ran NMEA. I pulled the receiver out of the Samsung-Symmetricom Z3805A and mounted the Furuno GPS receiver in a stand alone receiver enclosure and all I could see it doing was generic NMEA at 9600 BPS.
> 
> I understand the moving, I have also just moved.  I am very much interest in your replacement efforts.
> 
> Just for info, to the list, the Hewlett-Packard Z3805A used Motorola GPS receiver in the binary mode. Also the Z3801A.
> 
> Somewhere down the line, after H-P sold the Time-Frequency division to Symmetricom, it appears Symmetricom redesign the Z3805A units.  The main PC board on the bottom of the Z3805A looks like the original in the Z3801A, Z3805A and the 58303.  The switching power supply board mounted above it looks the same. Some models used the HP double oven 10811 oscillator and then they changed to using the MTI-260 oscillator mounted on a new PC board and it doubles the 5 Mhz output of the MTI-260 to 10 Mhz.  Also the Furuno GPS receiver GT-8031B is a 12 channel receiver and I regularly see the GPSDO running with 9-10-11 satellites in GPSCon software.  It just has the March 2005 rollover date problem, like a lot of elder GPS receiver.
> 
> 
> 
> On 11/10/24 23:42, Scott Qi via time-nuts wrote:
>> Hi, it is a old version of NMEA protocol, I ever made a PCB (using GT-8031F card) this year to replace it (correct the GPS rollover problem), but seems few people need it, so I did not sell it, now I am moving, need to find which box include the PCB (I have more than 50 boxes to move).
>> 
>> for the old Z3801A or Z3805A, using Motorola M6 or M8 GPS module, need to upgrade the firmware (replace the 4 firmware chip easily).
>> 
> 
> 
>> On 11/11/2024 12:19 AM, Tom Knox via time-nuts wrote:
>>> Hi,
>>> I would look at Synergy they have a number of UBLOX modules specifically designed for vintage Motorola
>>> receivers.
>>> Cheers,
>>> Tom Knox
>>> 
>>> ________________________________
>>> From: bryon via time-nuts <time-nuts at lists.febo.com>
>>> Sent: Sunday, November 10, 2024 9:45 PM
>>> To: time-nuts at lists.febo.com <time-nuts at lists.febo.com>
>>> Cc: bryon <kd4fm at aol.com>
>>> Subject: [time-nuts] Samsung-Symmetricom GPSDO Rollover Problem
>>> 
>>> I have a Samsung GPSR, which is a Symmetricom Z3805A.  It looks like a
>>> Z3801A, except it has a front panel power switch.  On the rear panel it
>>> shows its made by Symmetricom and it has stickers inside on the PCB
>>> showing Symmetricom Z3805A, etc.  Runs off of 28 volts DC.  It also uses
>>> the MTI-260 5 Mhz oscillator on a 5 Mhz doubler board to get back to 10 Mhz.
>>> 
>>> The unit runs, but it has the March 2004 rollover date problem.
>>> 
>>> The unit uses a Furuno GT-8031B GPS receiver.  The GPS receiver has the
>>> form factor of a Motorola M12+ receiver and then the Furuno receiver is
>>> mounted on an adapter board that has the form factor of the elder
>>> Motorola PVT/Oncore VP receivers.
>>> 
>>> The Furuno runs 9600 BPS and the basic data sheet states it runs NMEA
>>> like protocol.
>>> 
>>> I attempted to put a LEA-6T and a M12+ into NMEA mode at 9600, but they
>>> will not do it.  I think its because they are timing only receivers and
>>> only run binary.  I also tried to put a Motorola Oncore VP in the unit
>>> that was set to the 6 channel mode and binary and the Samsung unit gave
>>> a front panel fault about 30 seconds after power up.
>>> 
>>> Does anybody have any experience with a replacement GPS receiver for
>>> this unit ?
>>> 
>>> Thanks.
>> 
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