Patent GB-710384-A (GB)
Title: Improvements in or relating to frequency shift telegraphy
IPC: B62M9/00
Filed: 1952-03-14
Abstract: 710,384. Multiplex radio signalling. SIEMENS & HALSKE AKT.-GES. March 14, 1952 [March 14, 1951], No. 6748/52. Class 40 (5) Relates to receivers for diplex systems in which a carrier frequency assumes four values f1, f2, f3, f4, for the four possible combinations of marking and spacing conditions in the two channels A, B, viz. space-space f1, mark-space f2, space mark f3 and mark-mark f4. The channel circuits each comprise phase-shifting and phase demodulating means by which direct currents representing the signalling conditions are produced. In all the embodiments described, the channel B circuit operates on the basis that for this channel space condition is signalled by either f1 or f2 while mark condition is signalled by either f3 or f4. In one embodiment, Fig. 2a, the four low frequencies into which the four carrier frequencies are converted and which are spaced at intervals of 400 c/s, are fed to a series resonance circuit L1, C1 tuned midway between frequencies f2, f3, Fig. 2b. The phase of the voltage developed across the capacitor C1, relative to that across the whole circuit, leads by nearly 90 degrees for frequencies f3, f4, and lags by nearly 90 degrees for frequencies f1, f2 as shown in the second graph. These two voltages are fed to a double push-pull modulator phase comparator GM2 and produce currents of opposite polarity for marking and spacing conditions in the, polarized relay B. The channel A circuit operates on the basis that for this channel space condition is signalled by either f1 or f3, while mark condition is signalled by either f2 or f4. The channel circuit feeds frequencies f2, f3 unchanged through band-pass filter BP1 to the series resonant circuit L2C2 while the frequencies f1, f4 are transposed. For this purpose, all the frequencies are fed to a modulator GM1 supplied also with a frequency fm, Fig. 2b, which is equal to f4-f1. The output is passed through band-pass filter BP2 passing the range f1, to f4, thereby selecting the resultant frequencies f4' and f1<SP>11</SP> which occupy the same places as f1 and f4 respectively but are due to the presence of f4 and f1 respectively. The subsequent action of circuit L2, C2 and the phase comparator GM3 produces currents of opposite polarity for frequencies f4<SP>1</SP>, f2 and f3, f1<SP>11</SP> respectively in the polarized relay A. In other embodiments for receiving channel A, frequencies f2, f3 are interchanged, Figs. 3a, 3b (not shown), f4 is superposed on j2 and f1 on f3, Figs. 4a, 4b (not shown), and f2, f3 are interchanged with superposition of the other two frequencies, Figs. 5a, 5b (not shown) In a further embodiment, channel B is translated, as in Fig. 2a, by circuits LC, GM1, B, Fig. 6a, while channel A phase comparator GM2 is fed from phase shifters PD1 and PD2 which operate as shown in Fig. 6b. The curve #u3 shows the variation of phase with frequency in circuit PD1 and curve #u4 that in circuit PD2. These are so arranged that the phase angle difference between the outputs increases by 180 degrees from frequency to frequency, the two outputs being " in phase # for frequencies f 1 and f3 and " out of phase" for frequencies j2 and f4. The output of the comparator is thus of opposite polarities for marking and spacing conditions.