A MOSFET TRANSMISSION-LINE HIGH-POWER ELECTRON-NUCLEAR DOUBLE-RESONANCE SPECTROMETER

In the apparatus we are going to describe, since our ultimate aim was its broadband behavior, a very large irradiating rf field up to 80 G can be obtained from 1.0 to 50 MHz on the sample inside the microwave cavity. A mean power of 300 W was attained by suitably combining four homemade rf amplifiers. Two Motorola MRF 174 metal-oxide-semiconductor field-effect transistors (MOSFET) were used in each of the amplifiers. Broadband behavior was achieved, while retaining the principle already used of stepping down the rf amplifier output impedance, by introducing into the spectrometer a flat transmission line with the correct characteristics. Examples of electron-nuclear double-resonance (ENDOR) spectra are reported and compared with those obtained on an earlier spectrometer.