Every dipole is fed via a power cable (characteristic impedance 50 ohms) which leads vertically from the base of the centre mast to the feeding point of the dipole on top of the mast.
A design was to be found in order to allow the tuning of the impedance at feeding point of the dipole. This impedance should correspond as close as possible to characteristic impedance of the cable.
At the same time it was necessary to provide a balun for the symmetrical dipole and the unsymmetrical cable. Both tuning and baluning were realized by a stub ( a short circuited line ) connected to the feeding point at the dipole and consisting of the feeder cable and a rigid tubular line. Feeder cable and a rigid tubular line are in parallel and fixed to the mast by means of insulators.
By adjusting the length of the stub most of the reactive part of the antenna impedance is compensated. Length and width of the dipoles are designed to obtain a real part of the antenna impedance which corresponds to the characteristic impedance of the cable. Since the reactive part of the antenna is nearly zero the antenna impedance at the feeding point of the dipole is equal to the characteristic impedance of the cable and the standing wave ratio can be neglected.