| 摘要 |
618,589. Telegraph receiving-systems. COMPAGNIE GENERALE D'ELECTRICITE. July 3, 1945, No. 16956. Convention date, March 12, 1943. [Class 40 (iii)] The invention is applied to the type of phasereversal telegraph system described in Specification 449,999. In this system the first signal-element of a message which is of a predetermined and invariable phase is filtered, amplified and applied to a ring demodulator DM, Fig. 1, and is also filtered and applied to a ring-type modulator Xm which is slightly asymmetric and produces an output in phase with the initial signal element. This output controls the demodulator DM and, being in phase with the input thereto, produces a telegraphic signal in the receiver LOC of predetermined and invariable polarity. Subsequent phase reversals of the incoming signals produce reversals at both the input 4 and control terminal 7 of the modulator Xm and the phase of its output, once established, is unchanged. The two phases received will, however, produce unequal outputs from the unbalanced modulator Xm and hence signal distortion occurs. In order to avoid such distortion, a blocking circuit BL and a rectifier Rd are added as shown in Fig. 2. The initial signal-element is now amplified at V1 and applied to the input 2 of the demodulator DM and is also applied to its control terminal 6 via the normally open blocking circuit BL. These inputs being in phase, the outputs to the receiver LOC and modulator Xm are of predetermined polarity and the latter establishes an output in phase with its input, i.e. in phase with the initial signal-element. This output is delayed at F2, amplified at V2, again delayed by the rectifier circuit Rd and applied to the blocking circuit BL which then ceases to pass the received signals. The delay of Rd is sufficient for the output of the modulator Xm to reach the demodulator DM before the blocking circuit is closed. Subsequent signals are then dealt with as in Fig. 1, the blocking circuit remaining ineffective as long as transmission continues. |
