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A comment on FriendlyElec NanoPi R5S as PTP Grandmaster Clock with GNSS/GPS Discipline (2022).

Re:FriendlyElec NanoPi R5S as PTP Grandmaster Clock with GNS... by magicalhippo on Monday October 14, 2024 @06:43AM (#41836237)
Set up my own GPS-referenced NTP server using an RPi3, very easy. Needed to use a powered antenna though, that little PCB thing I got with the module just didn't cut it.

Been working augmenting it with a 10MHz ovenized crystal oscillator (OXCO) for kicks, in case GPS is offline. You can second-hand units cheap on AliExpress and Ebay, which is nice as they're pre-aged so shouldn't drift as much.

Quality can vary a bit between them, some have lived a hard life perhaps, so I suggest getting 5 and checking with a scope.

Chrony somewhat recently gained support for multiple PPS sources, so should be able to just hook it up. This means I shouldn't need to worry about the absolute frequency of the OXCO as long as it is stable, which is nice.

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Re:FriendlyElec NanoPi R5S as PTP Grandmaster Clock with GNS... by willis936 on Monday October 14, 2024 @07:48AM (#41836629)
The phase of the OCXO's PPS will need to be disciplined to GPS, otherwise your offline time reference will be a stable, low jitter, and wrong.

Edit: I see you mean not feeding in PPS, only 10 MHz where phase doesn't matter. I didn't know Chrony supported that. You could also use a good reference multiplied to replace the Pi's clock.

Gepetto's GPSDO has been tempting to me for a long time. I've just never had an application to justify the cost.

https://www.tindie.com/products/nsayer/gps-disciplined-ocxo/

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Re:FriendlyElec NanoPi R5S as PTP Grandmaster Clock with GNS... by magicalhippo on Monday October 14, 2024 @08:30AM (#41836897)
Sorry, sloppy wording. My circuit will allow for both, with a small uC doing the 10MHz to PPS division and also run a DAC to control the OXCO fine-adjustment.

But I figured I'll try the simple approach first.

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