A kit for the conversion of an X-bandesr spectrometer for K-band operation is described and its performance has been tested withp-benzosemiquinone, vanadyl acetyl acetonate and 2, 5-ditertiary butyl semiquinone. The easy conversion of the X-band spectrometer to K-band operation enables us to distinguish between magnetic field dependent and field independent parameters. A varactor harmonic generator is used as a frequency doubler driving the fundamental power from the existing X-band source to give a power output at K-band without having to modify the electronic circuit; the modification of the microwave circuitry is proposed.

A computer-controlled X-band time domain electron paramagnetic resonance (EPR) spectrometer, with a time resolution of the order of 0.5μsec, has been constructed with many of the crucial microwave components designed and fabricated by the Microwave Engineering Group of TIFR. The spectrometer operates either in a microwave power pulsed mode for determination of spin-lattice relaxation times by the saturation recovery technique or in the kinetic mode for determination of the time dependence of EPR signal after laser excitation. It has an automatic frequency control, an automatic phase control and, most importantly, a field-frequency lock which ensures good stability of the EPR line positions enabling signal averaging for extended periods. The constructional details of the spectrometer and its performance in both the modes are described here by reporting results on certain typical systems.