This paper presents a survey about problems to be expected to arise with two simultaneously operating transmitting sets with closely spaced, tuned antennas. At first both the possible types of mutual influence are presented: active and passive influence, an overcoupling of power from one transmitter into the other leads to a so called active influence, whereas any reduction of transmitting operation by means of mistuning another antenna in the reactive short range field shall be called passive influence. The following consideration will be restricted to passive influence via short range antenna coupling. A theoretical investigation of these facts is followed by a description of a simple measuring set, suitable to investigate quantitative mutual passive influence. A new method for the first matching procedure for programmable matching units is presented. It provides a constant standing wave ratio, not depending on the other matching units state.