Patent GB-578301-A (GB)
Title: Improvements relating to radio direction finders
IPC: H03J7/32
Filed: 1942-07-31
Abstract: 578,301. Wireless direction -finding apparatus. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). July 31, 1942, No. 10730. [Class 40 (v)] Radio direction-finding apparatus includes a receiver with an omni-directional aerial and means for automatically and cyclically varying the tuning so as to scan a frequency band, means for producing on an oscilloscope screen indications corresponding to the frequencies of transmissions received during the scanning, means for interrupting the scanning and tuning the receiver to a selected one of the indicated transmissions, and means for determining the direction of propagation of this transmission. A number of forms of apparatus are described, in some of which means are provided for indicating simultaneously on the oscillograph screen the selected frequency to which the receiver is tuned and the direction of propagation of the corresponding transmission. In one form of apparatus, Fig. 1 (not shown), the condenser shaft of a receiver connected to an omni-directional aerial is rotated by a motor, and the output current of the receiver is applied to.a rotary potential divider which is mounted on the same shaft and is formed and connected to the orthogonal deflection plates of an oscilloscope in known manner so as to give a circular trace on the screen with radial deflections at the points corresponding to the frequencies of received transmissions. The direction from which any one of these transmissions is being received may then be determined by stopping the motor, tuning the receiver manually to the desired transmission, connecting it to a rotatable directional aerial system, and adjusting this system until the deflection of the oscilloscope beam vanishes, indicating that the aerial system is in the angular position of minimum reception. In a modification, Fig. 3 (not shown), the circular trace and radial deflections of the beam are produced magnetically by a deflecting coil traversed by the output current from the receiver and carried by the condenser shaft so that it is rotated around the axis of the oscilloscope synchronously with the tuning condenser. The manual setting of the condenser is indicated on the oscilloscope screen by a radial line, produced by supplying an interrupted current to the deflecting coil. As the tuning range extends over 180 degrees only, the beam is extinguished over the other half of its path in which the indications would be repeated by applying to a control grid a voltage derived from a rectifier to which high-frequency energy is passed from an oscillator by way of a member secured to the condenser shaft and formed so as during the half revolution to provide capacity coupling between fixed electrodes in the circuit between the oscillator and rectifier. Fig. 5 shows a further modification in which an indication 89 of the angular position of the directional aerial system is given simultaneously with those indicating the transmissions on the oscilloscope screen. The aerial system comprises directional antenna units 61, 62 connected to a goniometer 63, the arrangement being used during the frequency-band scanning operation as an omni - directional system. Signals received in the movable coil of the goniometer are passed to a receiver 64 and amplifier 78, the output of which is connected to a potential divider (or reversed goniometer) 77 on the shaft of the tuning condensers 65, 66, which during the detection of transmissions is rotated by a motor 69. The potential divider 77 is connected through an amplifier 72 to the deflecting system 71 of the oscillograph so that, as before, a circular trace is produced by the beam with radial deflections corresponding to the received transmissions. A rotary potential divider 82 on the shaft of movable coil of the goniometer 63 is fed from the amplifier 78 and connected, alternately with the potentiometer 77, to the amplifier 72 through a commutator switch 74, so that a spot appears on the screen indicating the angular position of the goniometer, which spot may be converted to a radial line by superimposing a high-frequency current on that supplied from the amplifier 78. The switch 74 is reversed mechanically at sufficient speed to cause apparently continuous and simultaneous indications of the transmissions received and of the goniometer adjustment. An " electrostatic switch" 81, comprising a member rotated by the motor 69, provides, during the half revolution in which indications are to be suppressed, capacity coupling between an oscillator 80 and a rectifier 79 which then blocks the amplifier 78. The receiver 64 is tuned manually by a knob 67 for selecting the transmission, the bearing of which is to be found. To allow simultaneous selection of a particular transmission and the detection of all transmissions within the frequency range, separate " selecting " and " detecting " receivers may be used. In one form of apparatus, Fig. 12 (not shown), the tuning condensers of a " detecting " receiver are continuously rotated to produce, as in the previously-described apparatus, indications of all transmissions in the frequency range, and a selecting receiver connected to a directional aerial is manually tuned to the desired transmission. An " electrostatic switch " or commutator on the continuously-rotated condenser spindle of the detecting receiver supplies during alternate half revolutions energy from an oscillator to the detection receiver, in order to block it, and to the rotatable coil of a reversed goniometer, which is mounted on the condenser spindle of the selecting receiver. The fixed coils of the goniometer are connected to deflecting plates of the oscilloscope, resulting in a radial deflection of the beam which indicates the tuning of the selecting receiver, and which occurs in the half-cycles during which the transmission indications produced by the detecting receiver are suppressed. Fig. 14 shows a form of apparatus using a " detecting " receiver 212 and " selecting " receiver 235 and giving simultaneously on the screen of the oscilloscope 201 indications of all transmissions within the frequency range, of the frequency to which the selecting receiver is manually tuned, and of the bearing of the transmission of this frequency, as shown on Fig. 16 respectively at 249, 252 and 253. The indications 251 are obtained, as before, by continuous rotation of the tuning condensers 206 of the receiver 212 by a motor 204, which also rotates the beam deflecting coil 202 to which the output of the receiver is supplied after amplification in an output stage 213. The manual setting of the condensers 227 of the receiver 235 is indicated by means including two goniometers 208, 228 having their pairs of stator coils connected as shown. The rotor 228s of the goniometer 228 is rotated with the shaft of the condensers 227 and receives highfrequency energy from an oscillator 215 by way of a transformer 234. The rotor 208s of the goniometer 208 is rotated by the motor 204. In these circumstances, the output from the rotor 208s has the frequency of the oscillator 215 modulated by the frequency of rotation of the rotor 208s, the phase of this modulation wave corresponding to the angular position of the rotor 228s, i.e. of the condensers 207. This modulated output, consisting of halfwaves as shown in Fig. 15 is supplied via a transformer 233 and amplifier 216 to another portion of the output stage 213 having a tube whose cut-off point is at P so that only the tips 243 of the half-waves are amplified, furnishing the indication 252 on the oscillograph screen. To distinguish this indication, it may be made to appear as a broken line by high-frequency modulation applied to the grid of the oscilloscope during its appearance. The direction of the selected transmission is determined by manual adjustment of directional receiving means 239 for minimum reception, an indication 253 of the angular adjustment being produced by one of the means already described. Rectified blanking pulses are applied from the oscillator 215 by way of a rotary electrostatic switch 207 alternately to two amplifying units in the output stage 213, and a switch in this stage applies the signals producing the indications 252, 253 alternately to one of these units, whilst the signals producing the indications 251 are amplified by the other, whereby all three indications are produced at different times.