Speaker
Description
This Talk will briefly explain the different working principles of common affordable GPSDOs and demonstrate how to build one using an so far uncommonly used mechanic - disciplining the GPS receivers clock itself.
The full setup:
all we need is ..
- raspberry pi pico 4$ - a 5$ used OCXO from ebay
- an RS41 weathersonde (free, some hunting required)
- some resistors
The components have been selected to be easily available, cheap and easy to solder.
The pico is being used to generate a phase locked 26MHz clock from the 10MHz OCXO. This clock is soldered to the RS41 weathersonde to discipline the gps receiver itself. This enables the GPS receiver to report a clock bias which directly translates to the drift between gps time and our OCXO down to nanoseconds. A simple PWM-DAC on the pico is hereby able to steer the the clock bias with sub nanosecond accuracy - indefinitely.
Unlike most < 1000$ GPSDOs this provides SDRs with a reference this approach has no untracked residual frequency offset. A single initial time synchronization is enough to create hourlong observations in If a 10min Lightning slot is available, i could go into more detail about the clock generation using only a pico and future plans to miniaturize the concept on a custom PCB. I will bring the working GPSDO to the event and likely even a first PCB iteration.
