GB357532A - Electric circuits employing thermionic valves or the like - Google Patents

Abstract

357,532. Changing frequency. STANDARD TELEPHONES & CABLES, Ltd. and DUNHAM. C. R., Columbia House, Aldwych, London. June 12, 1930, No. 18027. [Class 38 (ii).] Comprises a distributer, for use as a frequency divider, wherein thermionic amplifiers are rendered operative in cyclic order so that all but one are disabled at any one instant. Thermionic distributer, Fig. 1, shows part of a multiplex transmitter in which carrier oscillations pass from a source P through transmitter contacts K1, K2 .., amplifiers V11, V21 .., and curbing valves Va, Vb, Vc, to a line LY, the valves V11, V21 .. being rendered operative in cyclic order so that the transmitter contacts Kl, K2 .. become effective in succession. The leads A, B, C, convey square-form impulses at phase intervals of 120‹, as indicated in Fig. 2, and the pairs of valves V11, V12 .., under the control of the waves A, B, C, interact so as to produce the above result. The leads HT, E, NT are permanently at -250 volts, 0 and -100 volts respectively. The valves are out of action unless their grid bias is more positive than -6 volts, and the circuit constants are such that valve V11 is out of action if either the wave A is in its negative half-cycle or the valve V12 is passing current, or both. All but one of the right-hand valves are passing current, so that the way through all but one of the left-hand valves is blocked by negative grid bias on this account. When however the point XO drops from its normal -2 volts to -10 volts (as described below) valve V12 ceases to pass current, the voltage drop in R122 is consequently reduced, and point Y1 rises from its normal -10 volts to -2 2 volts. At the instant when wave A reaches its positive half-cycle, therefore, valve V11 passes current, setting up in R112 a voltage drop which causes point X1 to fall from its normal - 2 volts to -10 volts and so prepare valve V21 of the next pair to become operative as soon as wave B shall reach a positive half-cycle. Thus the drop in potential has been passed on from point X0 to point X1, and in similar manner it travels along the series of valves in synchronism with the waves A, B, C. Similarly, when valve V11 blocks up again on the occurrence of the next negative half-cycle in wave A, point X1 rises to -2 volts and restores valve V22 to its normal (active) condition. This change also is passed on throughout the series of valves. The latter are connected in cyclic order, so that the changes in the potential of X0, described above, are effected under the control of the last valve in the series. A simplified system, Fig. 4 (not shown), employing fewer resistances is described also. In a frequency divider the distributer shown in Fig. 1 is adapted to yield a rectangular wave having a frequency 1/2, 2/3rds, 3/4, 1/4, or other simple fraction of the frequency of the square waves put into the leads A, B, C. According to Fig. 5 (not shown), six pairs of valves are connected in cyclic order; point X1 is connected to one and one of the points Y1, Y2 .. to another of the grids in a thermionic flip-flop device of the kind described in Specification 352,401, [Group XL]. The frequency is halved. The output of the flip-flop device is as shown at 10 .. 14 or 15 in Fig. 6 according as the point Y1, Y2 .. or Y6 is connected to an input terminal of that device. If different numbers of phases A, B, C, and of valve pairs V11, V12, V21, V22 .., be employed, different frequency ratios are obtained.