Patent GB-499028-A (GB)
IPC: H04W88/02
Abstract: 499,028. Wireless receiving systems. WALLACE & TIERNAN PRODUCTS, Inc. June 15, 1937, No. 16613. Convention date, June 20, 1936. [Class 40 (v)] A method of supervisory control of a wireless receiving system includes the application to the receiver of locally-generated signals to simulate the signals normally received and means operated by the receiver to give an indication of the failure of any part of the receiver to function in normal manner. In Fig. 1, the output of the receiver proper A is applied to the reproducer 14 and also to a relay amplifier E comprising an amplifier 34 and rectifier bridge 99 feeding a tuned relay D. The radio frequency output of an oscillator 33 controlled by a piezo-elcctric crystal 96 and modulated by a microphone hummer 10 is applied to the aerial input circuit 13 through an attenuator 11, screened conductor 98 and capacity coupling member 97a. The receiver and its associated supervisory circuits are put in operation for normal manual reception, intermittent monitoring and testing by means of two multi-contact three-position switches 20, 21. The operation of these switches on the receiving system is as follows: Switches 20 and 21 on right-hand contacts. The power supply from the 110v. mains is applied to the receiver A, and the filaments of the local oscillator 33 and relay amplifier 34, and the plate circuit of the latter, are energized from the potential sources G, H. With switch 21 to the right the circuit of the relay 74 is completed through contacts 76, 77 to the 6-volt source G. Operation of this relay causes a pivoted switch plate 79 to swing to the right thereby engaging contact 81 with the toothed cam 17. This cam forms part of a cycling mechanism driven continuously by a motor 12 at constant speed, which is supervized by a centrifugal switch device 61, 62, 64; if the motor 12 slows down or stops, the alarm bell B is energized by closure of contacts 63, 64 operating relay 65. Following operation of relay 74, the cam 17 now periodically makes and breaks the circuit of the microphone hummer 10 at a frequency of e.g. 5 cycles per second and the oscillator 33 is thereby modulated at this frequency. To test the receiving apparatus, the operator depresses successively switches 87 and 88 ; this applies plate potential to the oscillator 33 from the source H. Modulated oscillations which simulate the character of the signal normally received are impressed on the receiver input, and pass through valve 34 rectifier 99 to the relay D which is tuned to the modulation frequency. D is thus energized to operate relay 106 which actuates the alarm B through the reset switch 117, relay contacts 106 and contacts 120, 121 of cam switch 122. Relay 124 is also energized to hold on the alarm until switch 117 is depressed. The alarm thus indicates that the receiver is properly tuned and that apparatus E is operative. Switch 88 is now depressed to test the receiver failure alarm circuits ; this opens the oscillator plate circuit at 94, 95 and relays D and 106 are rendered inoperative. The circuit of alarm B is also closed through contacts 129, 130 of switch 88 and 112, 128 of relay 106. Ringing of the alarm shows proper failure indication, and the switch 117 is again depressed to turn off the alarm. Switch 20 to centre, switch 21 to left-hand contacts. This affords intermittent monitoring and intermittent listening by means of cams 134, 135, which make one revolution every 15 minutes. The cam profiles are shown in Fig. 2 (cam movement right to left). For the first 60 seconds (profile 134a) everything is energized (except the plate circuit of 33) and the valves heat up ; for the next 20 seconds (profile 134b) the plate supply is applied to 33 and for the first 10 seconds of this period (profile 135a) contacts 120, 121 of cam switch 122 open, while during the second 10 seconds (profile 135b) contacts 121, 140 close, and, if relay D is not operating, the alarm B rings until reset switch 117 is'pressed. During the next 10 seconds the alarm is removed from control by relay 106 (profile 135a) and for the last 30 seconds of the operative period (profile 134a) receiver A is set to receive signals from its distant transmitter. For the next 13 minutes the whole apparatus is de-energized. Switches 20 and 21 to centre contacts. The receiver A, oscillator 33 and amplifier 34 are continuously operative ; the microphone hummer 10 and relay 74 are energized every 15 minutes, plate voltage is connected to oscillator 33 and testing signal applied as before. In this position the receiver is operative for listening for 14¢ minutes, the remaining 30 secs. being employed for testing. Switches 20 and 21 to left-hand contacts. This gives "manual" operation ; the oscillator amplifier and cycling mechanism are all inoperative. When the operator has received an automatic call (as above) he throws 20 and 21 over to left-hand to listen on the reproducer 14. In the arrangement shown in Fig. 3, the receiver A comprises a radio frequency amplifier 200, detector and A.V.C. unit 201 and audio frequency amplifiers 202, 204, the loudspeaker 203 being fed from the first. Modulated high frequency oscillations from the oscillator are supplied over condenser 209 to simulate the normal signal for supervision purposes. These oscillations have the same frequency as those from the distant transmitter 212 and have such feeble amplitude that the A.V.C. controls the set to maximum sensitivity. The normally received signal from transmitter 212 is such that the receiver is not controlled to maximum sensitivity on its reception. If the receiver is operating correctly the non- selective relay 211 is energized on receipt of the local signal alone, and opens the circuit of the alarm 213. The modulation of the distant transmission is either zero or such that the amplifier 204 has negligible response thereto. Hence even with the combined input of distant and local signal the relay 211 is not energized and the alarm rings to indicate a call ; this follows since the sensitivity of the set has been decreased due to reception of the distant signal. In further modifications a relay tuned to the modulation frequency is provided additionally to the relay 211 and in parallel thereto ; the circuit is opened by 211 when the testing frequency is applied and the tuned relay actuates the alarm to indicate a call, Fig. 4 (not shown). The relay 211 may control the operation of a wireless transmitter to give distant indication of failure while the tuned relay actuates a foghorn etc.; or the relay 211 may, when actuated by failure of the receiver, operate to connect a spare receiver in place of that in use, Figs. 5 and 6 (not shown). Specifications 409,481, [Group XXXV], 459,235, 462,454, and 462,455 are referred to.