| 摘要 |
960,654. Personal signalling receivers. MINISTER OF AVIATION. Dec. 18, 1962 [Dec. 28, 1961], No. 46396/61. Heading H4L. A personal signalling receiver including an R.F. amplifier, a demodulator and an A.F. amplifier has a selector means responsive to a personal call signal and switching means which control part of the A.F. amplifier so that either it is caused to act as an oscillator on receipt of the call signal by the selector or it amplifies the signal from the demodulator. The transmitted carrier frequency is picked up by a coupled ferriter rod aerial 1 and is fed to R.F. amplifier 2, consisting of an oscillator mixer stage Q1, two I.F. amplifier stages Q2 and Q3, and at its output a detector stage D1 The output of detector stage D1 is applied to selector device 3 with two tone amplifier stages Q4 and Q5 driving a reed unit 8, 9 and 10 whose reeds 9 and. 10 are tuned to a single tone frequency or two separate tone frequencies comprising the characteristic call signal. When these reeds resonate together H.T. is applied to energize a double relay T/1 resulting in the closure of contact T1. The relay is locked by switch S1(b) in the position illustrated. The A.F. amplifier 5 has an amplifier stage Q6 and a push pull output stage Q7, Q8 whose output is applied to loud-speaker 6. A positive feedback connection 7 is taken from the output to a switch S1(a) which in the position shown applies positive feedback to the amplifier input converting 5 into an oscillator. Operation of stage 5 as an oscillator occurs on closure of relay T1 since H.T. is then applied to the relevant parts of circuit 5. On hearing the alarm signal at loud-speaker 6 the called person manually changes the switches S1(a) and S1(b) (normally ganged together) to their second positions. Changeover of switch S1(b) releases the relay T/1 and applies H.T. direct to stage 5. The movement of switch S1(a) to its second position, however, breaks the feedback line 7 and connects the output of detector stage D1 to the input of stage 5 which now functions as an A.F. amplifier to provide the operator with transmitted speech intelligence. A modification of the circuit is described, Fig. 3 (not shown), in which the unit 4 responds only to the sequential alternate reception of two different tones. A volume control is also provided. |
