Patent GB-1070472-A (GB)
Title: Antenna selector systems
IPC: H01Q3/24
Filed: 1964-05-29
Abstract: 1,070,472. Diversity receivers; transistor pulse generating circuits. STANDARD TELEPHONES & CABLES Ltd. May 29, 1964 [June 3, 1963], No. 22302/64. Headings H3T and H4L. Relates to arrangements in which one of a plurality of aerials is connected at any one time to a receiver: in the absence of a " usable " signal the aerials are connected sequentially and the first one affording a usable signal is locked on to the receiver. According to the invention the dwell period of the means sampling the aerials is individually adjustable for each aerial. The embodiments are for the utilization on an aircraft of radio navigation information transmitted from a " Tacan " beacon and incorporating a 125 c/s. signal (Fig. 2A). A peak signal detector (2, Fig. 1) affords a smoothed waveform having a delayed lagging edge (Fig. 2B) to ensure uninterrupted operation in the event of momentary loss of the input signal. Two aerials are used in this embodiment. A Schmitt trigger circuit (3) produces inverted rectangular waveforms (Fig. 2C 1 , 2C 2 ) the former of which inhibits the operation of an astable pulse generator (5), (Figs. 2D, 2E) the pulse spacing from which is switched by waveforms (Figs. 2H 1 , 2H 2 ) from an " aerial position memory " circuit (6). In the absence of a gating signal, the astable pulse generator causes the aerial position memory circuit to cycle between two aerials (1, 2) with predetermined dwell times. One pulse from the astable pulse generator is lost when the positive-going Schmitt trigger waveform (Fig. 2C 1 ) terminates; this loss is rectified by a differentiator (10), (Figs. 2F, 2G). Detailed circuit arrangements, Fig. 3.-The input 125 c/s. signal, after amplification by an emitter-follower 13 incorporating a Zener diode CR 1 , passes to a clamping circuit 15 ... 18 and thence to a peak detector 21 ... 24 incorporating the delay of lagging edge (Fig. 2B). After amplification and impedance transformation by a " Darlington pair " Q 2 , Q 3 , incorporating diodes CR 4 , CR 5  to compensate for D.C. temperature drifts of diodes CR 2 , CR 3  the signal at junction 29 is fed to Schmitt trigger 31, 32. The waveform (Fig. 2C 1 ) at the collector of transistor Q 5  actuates transistor Q 6  which, via Zener diode CR 6 , bridges capacitor C 5  in the unijunction pulse generator 39 so that no pulses are generated thereby. At the end of the gating period pulse generation commences (Fig. 2E); adjustable dwell periods are afforded by resistors R 25'  R 26'  The pulses pass via an emitterfollower Q s -to reduce sensitivity to noise- and pulse steering networks 55, 57, 59 and 56, 58, 60 to a bi-stable circuit 46, 47; anti-phase rectangular pulses (Fig. 2H 1 , H 2 ) arise at the respective collectors of transistors Q 10'  Q 9 . The positive pulse (Fig. 2F) to replace the one lost from the unijunction pulse generator is formed by capacitor C 4 , resistor R 30  and diode CR 7 . The D.C. level at the collector of transistor Q 10  determines which aerial is locked on to the receiver (Figs. 2I, 2J). Diode CR 16  prevents any maloperation due to reverse E.M.F. in aerial-switching solenoid 83. For use with more than two aerials the bistable circuit may be omitted, a stepping relay being actuated by the output of the unijunction pulse generator and independent, adjustable, dwell period resistors being incorporated (Fig. 4).