[time-nuts] Re: FPGA-based GPS NTP server project

[Bob Camp]

Hi

You don’t have to spend what the F9T’s cost simply to knock down the jitter. There are a 
number of uBlox modules that have sawtooth correction data and cost < $40 mounted on
on a board. 

Bob

> On Feb 12, 2023, at 6:51 AM, HÃ¥kan T Johansson <f96hajo at chalmers.se> wrote:
> 
> 
> Hi,
> 
> perhaps the uBlox ZED-F9T would be a suitable choice, on a RCB-F9T board?
> That looks like 8 ns jitter, and the UBX-TIM-TP message should give the sawtooth.
> 
> A 0.5 ns sampler I actually have on the FPGA.
> 
> Cheers,
> HÃ¥kan
> 
> 
> On Sun, 12 Feb 2023, Ed Marciniak wrote:
> 
>> Your mediatek GPS receiver is probably a really lousy pick for low jitter.
>> There are options from Navspark like the NS-T, other receiving chips/modules
>> from the same, as well as some uBlox parts that would do better.
>> There’s options with under 20ns jitter on those, and if memory serves
>> there’s one that’s available that with a good sky view and antenna might be
>> more like 8ns jitter.
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>> ____________________________________________________________________________
>> From: Bob kb8tq via time-nuts <time-nuts at lists.febo.com>
>> Sent: Saturday, February 11, 2023 4:38:23 PM
>> To: Discussion of precise time and frequency measurement
>> <time-nuts at lists.febo.com>
>> Cc: HÃ¥kan T Johansson <f96hajo at chalmers.se>; Bob kb8tq <kb8tq at n1k.org>
>> Subject: [time-nuts] Re: FPGA-based GPS NTP server project  
>> Hi
>> If you want to get the short term jitter down to around a second or so,
>> set it up with a GPS module that puts out a sawtooth correction. You
>> also need to get the Arty A7 measuring at the 1 ns level. That’s do-able
>> without insane amounts of effort.
>> Bob
>> > On Feb 11, 2023, at 4:09 AM, HÃ¥kan T Johansson via time-nuts
>> <time-nuts at lists.febo.com> wrote:
>> >
>> >
>> > Hi,
>> >
>> > I have a NTP server project based on a Digilent Arty A7 FPGA board with a
>> MediaTek GPS MT3329.  Board-to-board NTP tests over network show about 20 ns
>> jitter, with long-term wanders of 100 ns, presumably due to my limited
>> sky-view.  More details:
>> >
>> > http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html
>> >
>> > Cheers,
>> > HÃ¥kan
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