Sense Determination from a Fixed Position

Author: J.B. Hoag

It is possible to determine from a single fixed position the sense of the signal, i.e., whether the transmitter is ahead of or behind the receiver along the line of propagation of the radio wave. This can be accomplished by using a vertical antenna in conjunction with the loop.

Fig. 34 G. A sense-determining radio-compass

As in Fig. 34 G, a short vertical wire is placed along the axis of the loop. The voltages induced in the directional loop and in the non-directional vertical antenna are combined in the mutual inductance M to give response curves of the types shown in Fig. 34 H.

Fig. 34 H. Principle of sense determination

If the vertical antenna voltage is equal to that of the loop, the two will add on the left, Fig. 34 H(a), and cancel on the right, to yield the cardioidal (heart-shaped) response curve shown. If the antenna voltage is too great, the curve of Fig. 34 H(b) will be obtained, while if too small there will be appreciable intensity of reception from the right. The coupling at M is adjusted until Fig. 34 H (a) is most nearly obtained. Then, for a radio wave approaching from the left, the signal will be strong, while if it is arriving from the right, the signal will be weak or zero. It is only necessary that the signal be noticeably stronger in the sense (direction) of the transmitter than in the reverse direction for this method to succeed, so that precise adjustment of M is not required. The procedure, then, is to determine the line of reception by the minimum method, with the loop alone, then switch on the vertical antenna and set for a maximum to get the sense. The procedure may obviously be reversed; the sense may be found first and then an accurate line obtained by the minimum method.