Patent GB-722600-A (GB)
Title: Radio frequency pulse repeaters
IPC: G01S7/38
Filed: 1944-03-24
Abstract: 722,600. Wiretess signaling; aerials. STANDARD TELEPHONES & CABLES, Ltd. March 24, 1944 [March 26, 1943], No. 5535/44. Classes 40 (5) and 40 (7). A pulse receiving and repeating system comprises an antenna, and a superheterodyne receiver, the pulse output of which triggers a modulator producing a pulse which is applied to the frequency changer to cause it to oscillate and retransmit pulses from the same antenna. In the arrangement of Fig. 1 pulse signals received by antenna 1 are fed by coupling loop 11 to a frequency changer 10 comprising valve 15 (V4), and the tuned circuit 12 and the local oscillator 21. The anode voltage of the valve 15 is such that oscillation does not occur but an intermediate frequency output is obtained which is fed through condenser 23 to the LF. amplifier 22. The output from the detector 26, is fed to a pulse amplifier 27 and the negative output pulse 32, Fig. 1, is fed to energize a trigger circuit 31 which produces a pulse 34, this pulse being fed to a modulator 35 which produces the large positive pulse 38 corresponding to the trailing edge of pulse 34. Pulse 38 is applied over condenser 40 to the anode of valve 15 and causes the frequency changer to break into oscillation and a pulse to be transmitted at a time after the receipt of a pulse determined by the duration of the pulse 34 produced by the trigger circuit 31. Circuit 31 comprises valves V1 and V2, valve V1 being normally biased substantially below cut-off while valve V2 has a very small grid bias. The negative pulse 32 is fed to the grid of valve V2 and due to the crosscoupling through condensers C1, C2 and resistors R1, R2, pulses 47, 50, Fig. 2, are generated at the anodes of valves V2 and V1 respectively while the corresponding grid' voltage variations are as indicated at 44 and 49 respectively. The negative voltage on the grid of valve V2 diminishes as indicated at 51, as condenser C1 is discharged through resistor R1, until the grid voltage rises above cut-off and the circuit reverts to its steady state, the duration of pulse 47 which is equivalent to pulse 34, Fig. 1, being determined by the time constant of the series circuit R1, C1 and thus by the variable resistor R1. The pulse 34 applied to the grids of the modulator 35, of which the valves V3 have the high impedance coil 36 in their anode circuit, causes a pulse of current 37 to flow in that circuit, the voltage generated across coil 36 being equal to the differential of the current wave and having the form shown at 38, Fig. 2. In order to prevent oscillation of the system, at least one valve in the intermediate frequency amplifier is blocked during the transmission of a pulse. The blocking valve 41, Fig. 1, has its grid energized simultaneously with the grid of valve V1, the positive voltage 49, Fig. 2, which is impressed on this grid causing the anode voltage of valve 41 to fall due to the drop through resistor R. The anode voltage wave is of the form indicated at 54 due to the time required to charge and discharge condenser C in the grid circuit of valve V in the I.F. amplifier. The grid of valve V is thus held below cut-off for that portion of the cycle during which the frequency changer is oscillating. The blocking voltage from the anode of valve 41 may also be applied to the grid of the local oscillator valve 57 as indicated. In a modified circuit, Fig. 3 (not shown), a negative pulse from the anode of the first valve in the trigger circuit is differentiated to provide negative and positive pulses. The second or positive pulse is applied to the grids of the modulator valves, which have a resistive anode load, to produce a negative output pulse which is applied to the cathode of the frequency changer valve to cause oscillation. The voltage for blocking the I.F. amplifier is obtained by integration of the negative pulse occurring at the anode of the first valve in the trigger circuit. The antenna, Fig. 1, is arranged primarily for the reception of horizontally polarized waves and consists of two members 2, 3 fed at their extremities through lines 5 and 6, a cross-over 9 which produces the correct phase relations at the extremities of the elements being inserted in line 5. In order to receive vertically polarized waves the repeater apparatus is enclosed in a housing 8, Fig. 1, which is made approximately one-quarter wavelength long at the operating frequency and of as small a cross-section as possible. The housing 8 is arranged substantially at right angles to the plane of antenna 1 and operates to receive and transmit vertically polarized waves by virtue of the coupling 7 to antenna 1.