2 ms·
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'
by magicalhippo 2y ago
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.
- willis936 2y agoThe 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/ https://www.tindie.com/products/nsayer/gps-disciplined-ocxo/
- magicalhippo 2y agoSorry, 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.