Patent GB-529712-A (GB)
Title: Improvements in or relating to wireless apparatus for the simultaneous reception of a plurality of signals
IPC: H03J7/32
Filed: 1939-03-17
Abstract: 529,712. Wireless signalling. WALLACE, M. March 17, 1939, No. 8588. Convention date, March 17, 1938. Addition to 525,393. [Class 40 (v)] [Also in Group XXXV] Several different signals, distributed over a wide band of frequencies, are received simultaneously by constantly varying the tuning of the set, as described in the parent Specification, and are then presented as separate traces on the fluorescent screen of a cathode ray tube. This allows the direction, field-strength, frequency, and other characteristics of the various signals to be simultaneously compared, particularly for the purpose of enabling an aviator to ascertain his position in the air. As shown in Fig. 22, a chart of the country to be navigated is superposed on the fluorescent screen of a cathode ray tube, and the incoming signals are shown, in varying amplitude, both on the vertical and the horizontal axes of the screen. By noting the co-ordinates of the signals from a given beacon station, its position can be identified on the chart, as indicated by the cross-hatched square. The grouping of the signals along the vertical and horizontal axes is effected by switching the " timing " or scanning voltage generated by a magneto 61a, 70a, Fig. 18, in synchronism with the reversal of contacts 143, 144, 145, between the tuning system and the deflecting-plates 9, 15 of the cathode ray tube. The form of the scanning- voltages produced by the magneto can be adjusted by varying the shape of the armature 61a and the associated pole-pieces. This method of direction finding may be used in combination with a network of beacon stations which covers the area to be navigated with beams having a frequency determined by the latitude and longitude of each beacon. Periodic variation of the tuning and timing voltages may also be effected by varying the inter-electrode capacity of an input valve by means of a dynatron-oscillator (Fig. 27, not shown), or by means of mechanically operated and ganged switches (Figs. 8 and 9, not shown). Various alternative means are described for varying the frequency-band over which the receiver can be tuned and for correlating the controlvoltages applied to the cathode ray tube (Figs. 1 to 4, not shown). In Fig. 5, two frame aerials 142, 143 are alternately switched into circuit at 145, 146, so that signals are fed first to one and then to the other of the deflecting-plates of the cathode ray tube, synchronously with the tuning and timing switches 110, 113 and 24, 25, respectively. Signals from the first aerial are shown on one side, and signals from the second aerial on the other side of the median-line of the fluorescent screen. The relative amplitudes of given signals then show the pilot which stations lie to the right of the craft, and which to the left ; or a frame aerial and a vertical aerial may be combined to give a narrow equi-signal course for " homing. " The frame aerial and cathode ray tube can be swung simultaneously through an angle, as shown in Figs. 12a, 12b and 12c, so as to indicate the location of each beacon station by the corresponding changes in amplitude of the signals, N. S, E, W along the axis of the screen. A receiving circuit is also described (Fig. 14, not shown) in which the trace of a station straight ahead appears as shown at A1, 'Fig. 16, whilst it takes one or other of the positions A2 or A3 when the machine is flying off-course. Fig. 25 shows an overlapping- beam transmitter O, with marker beacons f1 ... f5, transmitting signals of graded frequency, strung out along each of the course-lines, so that the aviator can identify his exact position at any time. A wider band of frequencies can be covered by periodically switching-over from one wave-band to another (Fig. 15, not shown) the signals in one wave-band being shown on a different part of the fluorescent screen from those on another wave-band. A local-oscillator valve (Fig. 28, not shown) may be used to calibrate the frequency of a visual signal, and to facilitate its reception on a loudspeaker.