Radio propagation at 84.125MHz: measurements with mobile receivers and in the presence of aircraft

The paper is concerned with an investigation of the propagation characteristics relevant to the operation of digital v.h.f. radiocommunication systems with mobile terminals. Appreciable information already exists regarding the statistics of signal-strength distribution as a function of range and aerial heights. However, comparatively little information can be found concerning the signal distortions likely to be produced by multipath propagation, by operation with a moving terminal, or by signal reflections from aircraft. Such information is required in order to assess the relative merits of different modulation and multiplexing methods and to permit prediction of performance against range. The digit rates of primary interest were about 20k bit/s, 150 bit/s and 75 bit/s. The complete paper describes relevant details of the equipment, an investigation of propagation characteristics with the receiving terminal in a moving vehicle, an investigation of the effects of aircraft reflections, and the possibilities of application of the propagation results to the design of digital transmission systems.