Provable 10MHz±0.01Hz (or better) into 50Ω at low cost
NOTE: I haven't figured how to run GitHub properly. Look at the latest release for most recent updates.
Files: Main.asm - the software written in PIC assembler. Read SettingUpMPLAB.pdf to create the .hex file.
SettingUpMPLAB.pdf - setting up MPLAB X V5.35 (the last version to support MPASM).
Software.pdf - an overview of how the software works.
GPSDO-2023-02-12_163841.zip - KiCad 6.0 files with schematic and PCB layout
Circuit.png - a printout of the schematic from KiCad 6.0 (to save you having to set it up)
GPSDOnotesV1.pdf - notes about commissioning and running the GPSDO
Notes: The schematic (and therefore the PCB) has a few optional bits.
- There are spaces for filter capacitors around the buck converter. Some converters require them. Some have them onboard so not needed on the PCB.
- There is provision for a precision regulator to supply 5V to the FET pair that generate the control voltage. It and associated components can be left out, a wire link can get the 5V from the OCXO regulator, with only a slight (hard to measure) degradation of performance.
- There is provision to acquire the NMEA data and 1pps from a remotely located GPS module via a line driver/receiver pair. This has been tested to 20 metres, but most people will get satisfactory results plugging the GPS unit into the PCB. In the testing, a socket was installed for the line receiver (a UA9639). Pulling the IC allowed the GPS to be plugged in directly without removing other components.
- Use of optocouplers is not strictly necessary but does ensure no earth loops with whatever is connected to the GPSDO.
Latest Update: 2023-04-13 - Latest source, hex, notes in Release V1.2