Hi how do i reduce the Drive Level Of the Crystal Oscillator in this Shortwave Transmitter Circuit? its Typically 100 uW with those newer crystals.

 

Hi how do i reduce the Drive Level Of the Crystal Oscillator in this Shortwave Transmitter Circuit?

Go down with the supply voltage, change C1/C2 ratio, decrease the current through the transistor.

In a self-limiting oscillator, the transistor operates in the non-linear saturation/cuttoff range and it is not possible to predict the expected drive level of the crystal. What you can do is measure the current through the crystal or do it in a simulation.

A solution to have predictable crystal dissipation is to run the transistor in linear mode and do the amplitude limiting externally with e.g. antiparallel diodes. The common collector Colpitts oscillator can be modified into a common collector Butler topology with the series resonant crystal in the feedback and with antiparallel diodes added at the base for limiting purposes. Pierce or Hartley type crystal oscillators can also be easily modified to limit drive level.

 

Go down with the supply voltage, change C1/C2 ratio, decrease the current through the transistor.

In a self-limiting oscillator, the transistor operates in the non-linear saturation/cuttoff range and it is not possible to predict the expected drive level of the crystal. What you can do is measure the current through the crystal or do it in a simulation.

A solution to have predictable crystal dissipation is to run the transistor in linear mode and do the amplitude limiting externally with e.g. antiparallel diodes. The common collector Colpitts oscillator can be modified into a common collector Butler topology with the series resonant crystal in the feedback and with antiparallel diodes added at the base for limiting purposes. Pierce or Hartley type crystal oscillators can also be easily modified to limit drive level.

What particular specs are required for the diodes?

 

What particular specs are required for the diodes?

Usually Schottky diodes are used due to their low 1/f noise but generic Si diodes (1N4148 or similar) are fine too.