GPS Disciplined Oscillator (GPSDO)

 As we go higher up in frequency, a GPS Disciplined Oscillator (GPSDO) is needed for good frequency stability. Homebrewers are familiar with the drift of our VFOs in yester years, making it difficult for the receiving station to track our signal exactly! GPSDO will have an antenna to get GPS signals for controlling the local oscillator signal. When the GPS signals are not being received, the stability will depend on the stability of the local oscillator. Higher stability of local oscillators can be obtained by controlling the temperature in a special housing. Crystal oscillators enclosed in a temperature controlled chamber to prevent expansion and contraction of the crystal which could cause frequency fluctuation, is known as Oven Controlled Crystal Oscillator (OCXO).

Now lower cost GPSDOs have become available which have high stability so that drifts will be only in the range of one hundreth of a Hz! With these it is even possible to track very small changes in frequency of the HF signal reflected from the ionosphere when the ionosphere height is changing as with a solar eclipse.



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