603,568. Radio navigation. STANDARD TELEPHONES & CABLES, Ltd. May 11, 1944, No. 9036. Convention date, July 1, 1942. [Class 40 (vii)] Relates to means for producing simultaneous speech and course indication signals on a single carrier in an overlapping beam beacon system. The speech signals may be superimposed on a two-course aural or visual indicating system and either of these may be combined with another perpendicular two-course aural or visual guide path operating on the same carrier frequency. In Fig. 1, the RF carrier from source 20 is modulated at modulator 21 by speech signals from source 23 and at modulator 22 by speech signals and the 1020 c.p.s. course signal from source 24, and the modulation outputs combined in the balanced bridge 25 of the type described in Specification 491,359. The modulation components are thus combined in phase at terminal 27 and applied through the balanced bridge 40 to aerial 2. Owing to the transposition 26, the modulation components are combined in anti-phase at terminal 28 suppressing the carrier and the speech side bands but not the course side bands which are radiated. from aerials 1 and 3 in phase opposition due to the transposition 10 in the feeder 8. The transmission lines 11 and 12 coupling bridge 25 to aerial 2 and to aerials 1 and 3 differ in electrical length by 90 degrees so that the course side bands radiated from the three aerials produce a directional lobe which may be reversed by operating the phase reversal switch 29. This operation is performed in complementary rythm by the keyer 31 to produce an aural indicating guide path. An additional visual indicating guide path at right angles to the aural path may be produced by modulating the carrier from source 20 at modulators 35 and 36 by distinctive frequencies e.g. 90 and 150 c/s., combining the outputs in phase and anti-phase in the bridge 33, and applying the bridge outputs to aerial 2 and aerials 7 and 9 as described more fully in Specification 563,007. Bridge 40 is provided to balance the signals supplied by the bridges 25 and 33. In the above system, the modulators 21 and 22 are not equally modulated and a modification is described, Fig. 2, for obtaining symmetrical modulation in which the 1020 c/s course signals are applied in push-pull, and through a 90 degree phase shifter 54 in parallel to the modulators 51 and 52 which differ from the modulators 21 and 22 of Fig. 1 in that the lower side band modulation products are suppressed. The outputs are combined in bridge 25 as before so that the upper side bands resulting from the push-pull signals are fed to aerials 1 and 3, the carrier being suppressed, and the upper side bands resulting from the parallel-fed signals together with the carrier are fed to aerial 2. Since these latter side bands-are in quadrature with the former, the electrical lengths of transmission lines 11 and 12 should be equal. The speech signals are fed to the modulators in parallel so that the resultant side bands are fed to aerial 2 only. Fig. 3 shows a modification of Fig. 2 for producing a visual indicating course line by aerials 1, 2 and 3. The twomodulating frequencies, e.g. 90 and 150 c/s., produced by alternators 61 and 62 are combined in the hybrid coil 63 so that one frequency, e.g. the 90 c/s., is in phase opposition at the two output terminals and the other frequency, i.e. the 150 c/s., is in phase coincidence. The output from the upper terminals is passed through a 90 degree phase shifter 54 so that in effect' a first set of 90 and 150 c/s. signals are obtained in the line 67 in phase quadrature with a second set in line 68, but with one of the second signals leading in phase and the other lagging in phase with respect to the corresponding signals of the first set. The two sets of signals are applied in push-pull and parallel to the modulators as in Fig. 2 and since the two sets of upper side bands fed to the central aerial 2 lead and lag in phase respectively by 90 degrees relative to the corresponding side bands fed to aerials 1 and 3, two overlapping lobes of differently characterized side bands are radiated simultaneously. The speech signals are combined with the parallel applied course signals by means of the hybrid coil 64, an attenuator 66 being provided in the line 67 to compensate for the dissipating network 65 of coil 64. Alternatively the two sets of phase-quadrature 90 and 150 c/s. signals could be produced by suitable generators and in Fig. 3a (not shown) two such sets of signals are applied directly to modulators corresponding to modulators 51 and 52 in Fig. 2 when the relative phases of the resultant upper side bands is similar to that produced by the system in Fig. 3. The speech signals are applied to both modulators in parallel, as in Fig. 1. The course line is not shifted by any phase change in -the modulators, but it is weakened and second harmonic distortion is produced. The presence of this distortion may be used as a phase check at a monitoring station. When a visual course is radiated from. aerials 1, 2 and 3, the visual course radiation from aerials 7, 2 and 9 should have different modulation frequencies or an aural course may be radiated from these aerials. All the systems described have the advantage that the course line is weakened but not shifted by amplitude changes in the modulator outputs. The mechanical modulation shown in Fig. 1 may be replaced by electronic modulation as shown in Specification 550,633 and the aerials 1, 2, 3, 7 and 9 may be of the type described in Specification 538,036.