A variable-capacitance cylindrical condenser for precision measurements, and a wavemeter for short wavelengths

摘要

The paper describes a form of cylindrical condenser which has been developed for precision measurements at very high radio frequencies. One cylinder is always totally enclosed by the other and the capacitance is varied by altering the distance between the axes of the cylinders. This distance is varied by rotating the inner cylinder about an axle which is eccentric with both cylinders. With the dimensions chosen, the capacitance is increased by 1 ????????????????F by rotating the pointer through 45???????° from the position of minimum capacitance; the total change of capacitance is 16 ????????????????F. The capacitance valuses engraved on the scale are determined by calculation and not by experimental calibration.It is shown by electrostatic principles that the end-effect capacitance is likely to be substantially constant as the position of the inner cylinder is varied, and this supposition is supported by several exacting tests by experiment; the validity of the calculated scale is thus vindicated. The condenser can also be used as a very small variable inductance; an important use of this appliction is for determining the residual inductance of the condenser, which is found to be about 0.05????????H. The paper also includes a tentative design for a short-range, short-wave absorption wavemeter in which the same principles of construction are used.