Test oscillator for study of drive level dependence of quartz crystals

Test oscillators, in contrast to passive measuring methods, are able to span the whole range of drive levels from noise to normal operation. This is important for simulation of start-up conditions for practical oscillators, as well as for checking filter crystals for operation in a wide range of signal levels. A wide-band, negative-resistance Butler oscillator is modified with a ramp generator, controlling the negative resistance. This is zero when the crystal is inserted; any transient electrical or mechanical shocks due to insertion cannot affect start-up of oscillations. Analog output signals represent crystal current and oscillator negative resistance. Amplification of hf-signals makes possible observation of low level oscillation (`second level of drive´). Repeated sweeps can demonstrate change of resistance between sweeps. The oscillator can serve as part of an automatic testing facility under computer control