Patent GB-385521-A (GB)
Title: Improvements in or relating to radio direction finding apparatus
IPC: G01S1/02
Filed: 1932-05-28
Abstract: 385,521. Directive wireless signalling. AGA-BALTIC RADIO AKTIEBOLAGET, 13, Kungsgatan, Stockholm. May 28, 1932, No. 15222. Convention date, May 30, 1931. [Class 40 (v).] A directional wireless system comprises a transmitter with a directional and a non- directional aerial system, the former producing a rotating beam of angular velocity corresponding to the low modulation frequency of the signals in the latter, or a harmonic thereof, the direction of the transmitter being indicated at the receiver by the phase difference between the low-frequency modulations received from the two systems. In one embodiment a lowfrequency generator LFG, Fig. 1, modulates at LFM the radio frequency produced by oscillator O1 and supplied to a non-directional aerial A. The oscillator 02 of a different radio frequency supplies the crossed loop aerials R1, R2 with energy modulated by the same low.frequency from the generator LFG, the modulating currents being two components, 90‹ out of phase, produced by the phase-splitting device FF and applied to the two carrier-suppressing modulators M1, M2 individual to the aerials R1, R2 respectively. This results in a rotating beam being radiated from the system R1, R2, the relative phases of the low-frequency-modulations from the two systems A and R1, R2 received at any point, being dependent on the direction of the receiver relative to the transmitter. To remove the 180‹ ambiguity, some of the energy from oscillator 02 may be applied to the non-directional aerial A, Fig. 4 (not shown). The complete valve circuits for this embodiment are described, Fig. 5 (not shown). In another embodiment, a common carrier frequency is used from oscillator O, Fig. 6, with different intermediate modulation frequencies for the two aerial systems produced by generators MFG1, MFG2. The low frequency generator LFG modulates the intermediate frequency from MFG1 at LFM, the resultant currents modulating the radio frequency from O at MFM3 for the non-directional aerial while the two phase-displaced components from FF modulate the intermediate frequency generator MFG2 and the carrier from O through channels M1, MFM1, and M2, MFM2, respectively for the two directional aerials. The ambiguity-removing energy is applied to the transformer T in the non-directional aerial circuit from a modulator MFM4 supplies from oscillators O and MFG2. In a further embodiment, the low frequency modulations are produced by a mechanical rotary transformer RT, Fig. 7, with a fixed winding S supplied with radio frequency current from oscillator 02. The two mutually perpendicular windings comprising the rotor, rotate at a suitable frequency and supply modulated currents to the two aerials RI, R2 through amplifiers F1, F2, an equalizing device FU being interposed between the latter: The motor M driving the rotary windings of transformer RT also drives a low frequency generator G supplying currents to modulate oscillator O1 in modulator LFM for supplying the aerial A, ,which also receives oscillations from oscillator 02 through amplifier F3 and transformer T, for removing the 180‹ ambiguity. In a further embodiment a multiple frequency generator MG, Fig. 8, provides harmonic frequencies a, a + 1, b -1, b, and b + 1, a and b being arbitrary values essentially differing from one another. The frequencies a, a + 1, and b are used to energize the aerial A, and the frequencies b - 1 and b + 1 are applied to phase-splitting filters FF1 and FF2 respectively so that from each are produced two currents with a 90‹ phase difference between them which are applied to the aerials RI, R2 as shown to produce-the rotating field. At the receiver, when two' carrier frequencies are used, two receiving aerials and detectors are employed, the outputs from the latter being fed to a phase indicator which indicates the direction of the transmitter. When a single carrier frequency is used the receiver comprises a single aerial followed by a detector, two intermediate frequency filters and two detectors feeding the phase indicator. Specification 357,640 is referred to.