Fading channel simulators

Summary form only given, as follows. In the light of a recent letter to the Editor (ibid., vol. 54. p. 1072, August 1966) it may be of interest to readers to know that water tank fading channel simulators of the type described in this letter have been in operation in the graduate electrical engineering laboratories both of the Polytechnic Institute of Brooklyn and of the Massachusetts Institute of Technology since 1964. The MIT unit was developed under the guidance of Prof. Jacobs and uses recirculated water jets as a source of disturbance. The PIB unit operates from 200 kHz to 4 MHz and uses both mechanical movement and/or air bubbles as sources of disturbance. The PIB unit has been described in the literature. Additional results from this unit are presented in a recent paper ("An electronic probability density machine," IEEE Trans. on Insrrumention and Measurement, vol. 15, pp. 25-29, March-June 1966) describing a probability density machine that provides a useful adjunct for such a simulator. Several additional papers describing work done on this unit are now in preparation. The PIB simulator is used regularly both by graduate students taking our Graduate Communications Laboratory course and as a research tool by M.Sc. and Ph.D. candidates.