Patent GB-701592-A (GB)
Title: Improvements in or relating to radio navigation aids for aircraft
Inventor: JOLLIFFE SIDNEY ARTHUR WALTER
IPC: G01S1/02
Filed: 1951-02-14
Abstract: 701,592. Radio navigation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 20, 1951 [Feb. 14, 1951], No. 3617/51. Class 40 (7). [Also in Group XXXVIII] A radio navigation system which radiates to an aircraft speech signals corresponding to its bearing with respect to a ground station, comprises, at the ground station a radio direction finder which operates, through a follow-up control system, to position a plurality of switches in accordance with the bearing of the aircraft and thereby to select, in sequence, from a plurality of speech records, those records corresponding to the hundreds, tens and units of the numerical value of the bearing angle, the composite signal reproduced in sequence from the records being transmitted to the aircraft. The radio directionfinder employed is of the type wherein a modulation-signal having a phase corresponding to the bearing angle is compared with a signal of reference phase. The modulation and reference signals, both of sinusoidal form, are applied to respective channels S, R, Fig. 1, and are amplified at 2R, 2S, limited and clipped at 3R, 3S, and then differentiated to produce alternate positive- and negative-going pulses, the positive-pulses being suppressed by the diodes 6R, 6S while the negative pulses are applied to valves 7R, 7S forming an Eccles-Jordan trigger circuit. The output from the Eccles-Jordan circuit which consists of a train of pulses whose lengths are proportional to the bearing angle is applied to cathodefollower valve 14 to charge condenser 18 to a corresponding potential. Condenser 18 is connected to the control grid of valve 19 which together with valve 20 comprises a bridge circuit controlling a polarized relay 27, 28 which when energized actuates a reversible D.C. motor 30 to drive the wiper arm of a potentiometer 23 to a position of balance, the wiper arm being connected to the control grid of the valve 20. The motor 30 also drives three wafer switches H, T, U, each having 180 contacts at equal intervals of 2 degrees. The "hundreds # switch H has all the contacts having the same value for the "hundreds" figure of the bearing-angle value connected together; likewise the "tens" switch T has all contacts corresponding to the same " tens " figure for the bearing connected together and the " units switch U has all contacts corresponding to the same unit figure for the bearing connected together. Fig. 2 illustrates apparatus controlled by the switches H, T and U. A photo-cell PE is situated within a transparent drum D on which are record tracks D1 ... D12, tracks D3 ... D12 having recorded thereon the speech sounds for the numerals 0 ... 9, track D2 the symbol QDM (meaning " reciprocal magnetic-bearing") in speech, and track D1 the station identity. In front of the tracks are shutters SH1 ... SH12 which normally prevent light from a lamp LS and passing through lens OS from falling upon the drum D and exciting the photo-cell PE. When co-operating with the ground station, an' aircraft radiates a message which is received by the direction-finder to position the switches H, T and U in accordance with the aircraft bearing. When the bridge comprising valves 19 and 20 is balanced and relay 27, 28 is de-energized, switch contacts are closed to start motor MD which rotates the drum D at a predetermined speed and, through gearing, the five-position switch 5SW at one-fifth this speed. In the first position of this switch (i.e. during the first rotation of the drum D the shutter SH1 is opened and the station identification recorded on the track D1 is reproduced by the photo-cell PE. Similarly during the second rotation of the drum, the symbol QDM is reproduced. During the third rotation of the drum, the switch 5SW co-operates with the switch H to cause the appropriate shutter to open to cause the number corresponding to the setting of switch H to be reproduced. During the fourth and fifth rotations the numbers corresponding to the tens and unit switches are reproduced. After a complete rotation of the switch 5SW the motor MD is switched off. The reproduced sound signals are applied in sequence to the amplifier PA and thence to a transmitter for radiation back to the aircraft. Transmission of range information, Fig. 4.-In a modification, in addition to the direction-finding apparatus previously described and comprising aerial system RA1 and direction-finding unit DUF1, there is provided a further off-set aerial system RA2 and direction-finding unit DUF2. When the aircraft X is following the landing path, the angular indication provided by the second direction-finder corresponds uniquely to range, and two switches at the output of DUF2 are positioned in accordance with the tens and units values of the range in miles. The unit SPR, corresponding to the apparatus shown in Fig. 2, comprises a drum D having 13 speech records thereon and 13 shutters, the additional record consisting of the word "range." A complete cycle of operations consists of eight rotations being as before, the word "range" being reproduced in the sixth rotation and the tens and units numerals corresponding to the range being reproduced in the seventh and eighth rotations.