High frequency electronic research at the Institut für Hochfrequenztechnik ETH, Zurich, Switzerland

Two selected topics of current electronic research at the Institute are reported in brief. The first concerns noise in FM demodulators at noise amplitudes comparable to signal amplitudes at the demodulator input. Owing to the nonlinearity of limiters and demodulators the rigorous mathematical treatment of the demodulation process becomes rather involved. A number of basic cases have been rigorously worked out by various authors. More complex cases (for example, frequency-compression systems) however can hardly be expected to be solved strictly. For this reason approximation methods have been developed in order to arrive at expressions permitting simple numerical evaluation of the more difficult cases not treated thus far. The application of the methods employed for a number of cases shows good agreement with the experimental results as well as with the theoretical results of previous authors. The second topic concerns the generation of large HF electro-magnetic fields inside a plasma by applied external fields below the plasma frequency. The application of a static cross magnetic field modifies the ordinary skin effect in the plasma. Earlier experimental work shows that high carrier densities in the plasma occur under certain optimum conditions. A satisfactory theoretical explanation of the effects measured does not exist so far. The results of a new theoretical approach to the problem are given and discussed. They agree rather well with the experimental facts, some of which are also shown as measured by the author.