Mode Separation in Oscillators with Two Coaxial-Line Resonators

The resonance frequencies of a capacitance-terminated coaxial-line resonator may readily be determined graphically. The graphical analysis shows clearly why separation of the various modes of resonance is possible in oscillators using two resonators. Mode separation is favored by the use of resonators that have a large difference in their products of characteristic impedance and terminating capacitance. Too great a difference in the CZ0o products may, however, result in the coincidence of two modes of resonance for certain tuning combinations. Measured tuning curves for a lighthouse-tube oscillator agree with predicted curves in their general aspects. The agreement is improved by considering the tube electrodes and leads as extensions of the coaxial lines, terminated in capacitances smaller than the lumped interelectrode capacitances.