GB545126A - Improvements in or relating to radio telegraph systems - Google Patents

Abstract

545,126. Wireless receiving systems. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. Sept. 28, 1940, No. 14673. [Class 40 (v)] In a radio telegraph system in which signals are radiated by intermittent interruption of a radio-frequency wave modulated by a low frequency tone, the receiving apparatus is arranged that it takes up the same predetermined condition when the transmission is disturbed whether by interference or by fading. Fig. 1 shows an arrangement which is a modification of the arrangement described in detail in Specification 540,839. The output from the second frequency changer D2 is fed through three low pass filters F, F<SP>1</SP>, F<SP>11</SP> to supply signalling paths SP, SP<SP>1</SP>, SP<SP>11</SP> feeding into a conversion circuit CC to which is also fed over an interference path IP an interference component taken through filters F1, F2, amplifier A3 and detector D3. The conversion circuit CC feeds a telegraphic relay circuit RC, security apparatus SA and recording apparatus such as a teleprinter TP. The conversion circuit comprises valves V3, V4, Fig. 2, arranged as explained in Specification 540,839 so that a signal marking impulse at input terminals 1, 2 causes anode of V4 to become more negative while an interference pulse at 3, 4 causes the anode of V4 to become more positive. Thus the effect of interference is the same as fading or as a spacing impulse and a false " mark is impossible. The rectified voltage at the grid of V3 corresponds to the strongest of the signals applied through rectifiers RS, RS<SP>1</SP>, RS<SP>11</SP> since the voltage set up across R7 passes the rectifiers so that the smaller signals are not operative. In a modification, Fig. 3 not shown, valve V3 is dispensed with by reversing rectifier R1 and feeding the voltages from the signal and interference paths in opposition to the grid of V4. In another modification a separate valve V3 is provided for each signal path, the strongest output being fed to V4. In a final modification each signal path has a corresponding interference path.