[time-nuts] tyco electronics A1025

[Bob Camp]

Hi

Maybe a bit more on a timing receiver:

GPS is (for some reason) better known for navigation than for timing. In navigation the receiver moves around a lot. In most timing applications, the receiver is stationary. When moving, the mathematical solution to the “where am I / what time is it” question has errors in both terms. Often consumer grade GPS’s “push” the error into the time side of the solution to make the location appear more accurate. There is a lot of debate over this actually making the location more accurate or simply being a result of sloppy code. 

In a timing situation, with the location fixed, you can eliminate the location variability from the math. This involves a survey (often an automatic feature) of the location. Once the survey is complete, the timing data out of the receiver improves significantly. With improvements in the survey, the data may improve even more. This mode of operation is of no use in a normal non-timing situation. It only shows up in devices with firmware written for timing. 

Like it or not, all GPS devices are made as cheaply as possible against a design specification. The PPS out of the GPS comes from a free running TCXO on the simple modules. Since the TCXO can be anywhere relative to the PPS, there is an error in the edge that is delivered. It’s commonly referred to as sawtooth error. On a timing receiver, this error can be measured by the firmware and reported to “higher authority”. 

—————

Does all this matter in all applications? No, of course it does not. It may well be overkill. That’s well worth considering along with all the other issues.

—————

Coming back to the original point:

You can get modules for < $20 with some or all of the features above. They may also have other nice attributes (documentation ….). I have no idea what the value of the A1205 is to you. It may well be free at this point. If it does have a cost, compare it to the other modules as you look at it.

Another consideration is that your A1205 may be in fine shape and a random device off of eBay may have spent part of it’s life under water. There is no one single answer, only a lot of things to consider. 

Bob


> On Dec 14, 2014, at 11:07 AM, paul swed <paulswedb at gmail.com> wrote:
> 
> Should have added. You get great documentation also and everything is well
> established and most likely will handle some 1024 week rollovers.
> The old stuff is quite annoying with respect to this.
> Regards
> Paul
> WB8TSL
> 
> On Sun, Dec 14, 2014 at 11:05 AM, paul swed <paulswedb at gmail.com> wrote:
>> 
>> Strongly agree with Bob. The neo 6 on ebay is a good example silly stupid
>> cheap!
>> Regards
>> Paul
>> WB8TSL
>> 
>> On Sun, Dec 14, 2014 at 9:46 AM, Bob Camp <kb8tq at n1k.org> wrote:
>>> 
>>> Hi
>>> 
>>>> On Dec 14, 2014, at 6:03 AM, Francesco Messineo <
>>> francesco.messineo at gmail.com> wrote:
>>>> 
>>>> Hi all,
>>>> I've just found an old anti-theft system (I think) for cars . It has a
>>> tyco
>>>> electronics A1205 gps module.
>>>> I've been unable to find any information about this module, other than
>>> it
>>>> should be a 3.3V 12 channel GPS module with serial NMEA output.
>>>> Does anyone have any informations about it? Even a pinout would help.
>>> I'd
>>>> like to use it as a cheap NMEA receiver for a stratum 1 ntp server.
>>>> Thanks in advance.
>>> 
>>> It’s unlikely that a consumer targeted GPS has a good dedicated PPS out
>>> of it. Finding one that will do position hold is even less likely. You can
>>> get modules that will do both for < $20 and have a documented interface.
>>> 
>>> Bob
>>> 
>>>> 
>>>> Frank IZ8DWF
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