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.
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.
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.
Comments
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.
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/
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.