Common-aerial working for v.h.f. communication

The use of very high frequencies for ship-to-ship and ship-to-air communication in the Navy has been seriously restricted by the difficulties of siting a sufficient number of aerials for the many lines required in some ships. This paper describes a method which has been applied to economize in the number of aerials, by combining a number of transmitters or receivers on the same aerial. Passive circuits only are employed and would have advantages on board ship even if the considerable difficulties involved in designing suitable valve circuits could be overcome. Each set is connected to the aerial through a highly selective filter of a type that represents a short-circuit across the feeder at frequencies remote from resonance. The effects of this short-circuit are removed by the use of connectors, approximately ¿¿ long, between each filter and the point of branching; the lengths of these connectors can be fixed without excessive loss. The results of measurements and ship trials are reported and it is shown that the losses introduced are smaller than those that may be caused by the use of inferior aerial sites. The theory of the method is briefly investigated.