| 摘要 |
<p>686,760. Radio signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 16, 1950 [Aug. 12, 1949], No. 21062/49. Class 40 (v). In a two-way radio communication system, a repeater station, on receipt of predetermined signals peculiar to that repeater, is arranged to repeat the signals back in the direction from which the signal was received instead of forward to the next station in the system. In this way the system may be tested station by station by looping each repeater back to the terminal station in turn. As shown, each repeater station in a frequency modulation communication system comprises a receiver R1 receiving on frequency f1 and feeding a transmitter T1 transmitting on f2, and a receiver R2, for the other direction, receiving on f3 and feeding a transmitter T2 which transmits on f4. Each receiver is provided with a demodulator whose output is fed to a filter F1 or F2 responsive to the allocated signal, which may be a tone signal of different frequency for each receiver. The filters are coupled to rectifiers D1, D2, respectively, the outputs controlling relays K1 or K2. If the relay K1 is operated by receiver Rl, it switches on an oscillator O1, of frequency f3-f2, and a mixer M1, which receives as its inputs the frequency f3-f2 and the frequency f2 from the transmitter T1, the resultant frequency f3 being fed to the receiver R2 and transmitted back on transmitter T2. Similarly receipt of the appropriate tone at receiver R2 will cause oscillator 02 of frequency f1-f4, and modulator M2 to be switched on, the output f1 being fed to R1 and transmitted back on T1. To prevent " ringing " the relays K1, K2 are interconnected so that when one is in operation the other is disabled. In a simplified arrangement the receiver may be provided with an extra piezoelectric crystal which can be substituted in the frequency changing circuit to render the receiver responsive to the appropriate transmitter at the same station, as described in Specification 670,302. Time delay circuits may be provided at a repeater station to ensure that when a predetermined signal has looped back that station it will remain looped back for a predetermined time after the signal ceases, to enable other signals to be sent round the loop for special test purposes. Reference has been directed by the Comptroller to Specification 652,111.</p> |
