VHF FILTER CRYSTAL RESEARCH.

Abstract : The resonant frequency of a 20 MHz AT-cut fundamental mode resonator was lowered, in 20 kHz increments, a total of 400 kHz (2%) by depositing SiOx. The Qm of the fundamental, third, and fifth harmonic modes was determined as a function of the decrease in the resonant mode frequencies. These preliminary data indicate that dielectric tuning initially has little or no effect on resonator Qm. As the resonant frequency is further lowered, however, the Qm eventually begins to decrease linearly with the frequency. The latter appears to be a result of excessive mass loading of the entire resonator structure. Initial date were obtained on the effect of air loading on the Qm of fundamental, third, and fifth harmonic mode resonators. Measurement techniques are discussed and experimental data are presented to indicate the accuracy of the transmission line method in determinations of the resonant resistance of VHF crystals (10-100 MHz) in a vacuum system. The CdS-quartz composite resonator is discussed briefly. (Author)