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Re: Low cost GPS receiver?

From: Daniel O'Connor
Subject: Re: Low cost GPS receiver?
Date: Wed, 5 Apr 2023 11:01:11 +0930

> On 2 Apr 2023, at 10:42, Daniel O'Connor <> wrote:
>> On 2 Apr 2023, at 07:10, Hal Murray <> wrote:
>> said:
>>> For NTP purposes USB is fine, and solves both the communications and power 
>>> in
>>> the same cable and you don't have to do any soldering either :) 
>> That depends on if you want good time or crappy time, and what your versions 
>> of good and crappy are.
> Naturally, and what you consider 'low cost' :)
> At work we have an FTDI RS232 TTL cable connected to a uBlox M8T (that is 
> inside a rack in a radar system) that NTP talks to with PPS capture because 
> we don't control the firewall so NTP packets are blocked and it suffices to 
> keep time well.

I setup ntpviz for it, here's a static grab of the last few days:

>> I'm interested in better than you can get via USB with the ones I've tried.
>> The firmware in most/many GPS modules seems to do a poor job of scheduling 
>> the 
>> serial transmissions.
> Do you have PPS connected?
> At least on FreeBSD you can tell the ucom driver to capture DCD or CTS with 
> the PPS infrastructure which is what I use above.

FWIW the uBlox M8T has a USB interface built in which generates DCD/CTS edges 
on the port with PPS.
With something like and a reasonable 
antenna you should be good to go.

Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
-- Andrew Tanenbaum

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