Measurement of High Q at High Frequencies

A high Q tuned circuit is shock excited by the pulsed interruption of current flow through a pair of charge-storage diodes. The resulting damped oscillation is recorded via an FET source follower on a CRO or X-Y recorder. The Q is calculated from the observed logarithmic decay period. A Q of over 900 is readily measured at 60 MHz. The method is useful in the measurement of varactor series resistance and in the checking of the loading imposed by other components. The accuracy of the method is also discussed.