SDG #026 Symmetricom GPSDO 10MHz Reference Part 3

The third and final instalment of the Symmetricom GPSDO conversion turns a surplus telecom oscillator module into a finished piece of bench equipment. The focus is integration rather than characterisation: fitting mains power, output buffering and a usable user interface inside one enclosure without compromising the stability that makes a GPS disciplined oscillator worth building in the first place.

Power comes from a Meanwell MSP-100-48 medical grade supply, chosen because the original module expects a 48V rail and because a lower noise, low leakage supply is a sensible choice when it sits close to a precision OCXO. Running it internally removes the external adaptor and the associated cable clutter, but it also requires consideration of heat and radiated noise inside the case, which is exactly the sort of trade-off that separates a working prototype from a permanent instrument.

The custom PCB handles amplification and distribution of the OCXO output, so the reference can feed several instruments at once at a sensible level rather than delivering one marginal signal. That is the practical difference between a curiosity and a genuinely useful house standard for counters, oscilloscopes and signal generators.

The build is completed with a machined front panel with a vacuum fluorescent display showing GPS data such as satellite lock and status. It is not strictly necessary for the oscillator to work, but visible confirmation that the unit is locked and disciplined matters when it is trusted for measurements. Anyone considering a similar surplus GPSDO project will find this a realistic look at the mechanical, power and interfacing work that follows the initial teardown.