Patent GB-684077-A (GB)
Title: Improvements in or relating to radio direction finding systems with remote indication
Inventor: GARFIELD WILLIAM LITTERY
IPC: G01S5/00
Filed: 1951-07-24
Abstract: 684,077. Radio navigation; frequency modulation; pulse modulation systems. STANDARD TELEPHONES & CABLES, Ltd. July 24, 1951, No. 17511/51. Classes 40(v) and 40 (vii). [Also in Group XL (b)] An arrangement for remotely indicating the direction of propagation of radio energy received by a radio direction - finding station which produces a plurality of electrical quantities (e.g. voltages) jointly representative of said direction comprises translating means each arranged to translate a respective said quantity into a characterized train of pulses of repetition frequency dependent on the magnitude of the said quantity, means for jointly transmitting said trains to indicating means including receivers each arranged to receive a separate one of said trains and generate an operating signal equivalent to the corresponding electrical quantity for obtaining an indication of the direction of propagation. The direction-finder 1 may employ a continuously rotating loop or goniometer or comprise two loops or Adcock pairs a comparison of the amplitudes of the signals received by which gives the angle (#) the direction of propagation makes with a reference direction. In the embodiment described it assumed that four voltages: M+E Cos #, M - E Cos #, M+E Sin #, and M - E Sin # are the outputs of the direction finder over lines 2, 3, 4 and 5, respectively and these may be applied directly to trigger circuit 6 and local indicator 7 to give a bearing indication 8. For transmission to a remote indication the second and fourth of these voltages are in effect redundant as they may be derived from the first and third at the indicating station. It is thus necessary to transmit the voltages on lines 2 and 4 only. The voltage on line 2 is fed to control the frequency of saw-tooth generator 19 the frequency of which may vary between 10 and 50 c/s. according to the input signal. A feedback linearizing arrangement consisting of convertor 21 and counter 20 is provided for the generator 19. The saw-tooth waveform is used to control keying device 22 which passes pulses of tone from 1020 c/s. generator 23 for application to line 12 through band-pass filter 24. A similar translating device 17 is used to convert the potential on line 4 into a pulse frequency modulated signal for application to line 12 but the frequency of the tone generator is made different, say 2220 c/s. In one of the indicator receivers 13 filter 25 selects the keyed energy from oscillator 23 and passes it to amplifying and detecting unit 26. The pulse output from detector 26 is squared and differentiated at 27 before being applied to trigger circuit 28 which gives pulses of fixed amplitude and duration of the same recurrence frequency as the input pulses. These are applied to counter circuit 29 which generates output potentials similar to those on lines 2 and 3 for application to trace generator 14 and indicator 15. A similar receiver 18 receives the pulse train from translator 17 and generates output potentials similar to those on lines 3 and 4 which are also applied to the trace generator and indicator. An alarm circuit 30 is provided in connection with each receiver to give a warning if no pulses are being received. The saw-tooth generator. The generator 19 is a relaxation oscillator. The condenser 31 (Fig. 2), is charged through pentode 32 at a rate dependent on the valve's grid potential and when the potential across it reaches a certain value thyratron tube 34 strikes and discharges it ready for a further cycle. The saw-tooth output is derived at 35, the main input fed in at 36 and the input from the linearizing feed-back circuit at 37. A fixed potential is applied at 38 which determines the " frequency range " of the generator. The counter circuit. Circuit 29 receives pulses of fixed duration, standard initial amplitude and shape, Fig. 5(d), (not shown), and these are applied to the grid of valve 40 which is over-driven for the duration of the pulse and has a high resistance 41 in its anode circuit. The square waveform pulses comprising the anode voltage of valve 40 are fed through a smoothing network represented in the Figure by a single section 43, 44, although in practice it may combine many sections, to cathode follower valve 42, the output potential being delivered at 45. A portion of the anode potential of valve 40 is tapped off resistor 40 and applied to amplifier 47 which has a similar high anode load resistor 48, smoothing network, and cathode follower, reproducing at 52 a potential corresponding to that on line 3 (Fig. 1), while the potential at 45 corresponds to that on line 2.