| 摘要 |
341,568. Wireless signalling. BROENTJES, W., 40, Volkerakstraat, Amsterdam. Oct. 24, 1929, No. 32351. [Class 40 (v).] In a system of secret wireless telegraphy transmission, one group of working frequencies is used for the signals and one group of open-circuit frequencies between the signals, the working and open circuit frequencies being interchanged at will amongst themselves and as groups during transmission. The groups of frequencies used are known to the sender and receiver alone, and are transmitted directly or as modulations of higher frequencies. The changes are effected manually or automatically after a warning signal. In the arrangement shown, the anode inductance tappings 13 .. 18 are connected to a disc switch having a rotating arm M which successively connects various tappings across combinations of the variable condensers kl, k<2>, k<3>. The contact arm M is rotated step by step by a toothed disc B actuated by an escapement D which is in turn controlled by coils W2, W1, respectively energized by the working contact and " open circuit " contact of the transmitting key S. A different frequency is transmitted for each step of the arm M, the tappings 13, 15, 17 determining the open-circuit frequencies and 14, 16, 18 the working frequencies. The open circuit frequencies may be given the character of working waves by interrupters o<1>, o<2>, o<3>, which may be short-circuited by switches s, s<2>, s<3>. The opencircuit and working frequencies may be interchanged by change-over switches c<1>, c<2>, c<3>. A tuned intermediate circuit, similarly controlled by a switch arm actuated by the disc B, may be provided between the aerial and anode or grid circuit of the valve Z, in which case the condensers k<1>, k<2>, k<3> should be mechanically coupled to those of the intermediate circuit. The receiver has a number of tuned circuits, one for each working frequency, connected to a common detector valve so that it is unaffected by change from one working frequency to another. |
