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The complete electronic system of a frequency-sweep 240 MHz NMR spectrometer working with a superconducting magnet is described. Full circuit and construction details are given for the rf sideband generator, pretuned coaxial cavity, af aperiodic synchronous detector, digital frequency synthesizer as well as a phase-coherent, variable-frequency, time-sharing pulse generator. This system, with multichannel irradiation possibilities uses extensively standard integrated logic circuits and can be inexpensively built by any laboratory engaged in NMR research.

A large signal opto-microwave modeling technique is developed for an InP/GaInAs heterojunction bipolar phototransistor. The DC and RF parameters as well as the optical parameters extraction methods are described. Then an investigation of the maximum available gain is made using three-port considerations to determine the optimal load impedances. Opto-microwave Sparameters and an opto-microwave gain describing the transfer from the optical input to the electrical output of the phototransistor at millimeter-wave frequencies are defined. This study demonstrates the importance of the base load impedance on the opto-microwave transfer from the optical input to the collector output of the InP/GaInAs heterojunction bipolar phototransistor, and therefore on the phototransistor responsivity.