GB306493A - - Google Patents

Abstract

306,493. Lorenz Akt.-Ges., C. Feb. 21, 1928, [Convention date]. Copying - telegraphs. - In a picture telegraphy apparatus, synchronizing signals due to periodic variation of the grid bias of a thermionic valve are superimposed on the picture signals, which are also introduced into the valve, the receiver being such that the synchronizing signals are not manifested on the picture record. Picture signals, represented by shaded areas b, Figs. 1 and 4, are produced either with a stylus or by an optical method from the picture on drum 1, Fig. 2, and control the grid potential of the valve 3, the anode of which is joined to the grid of the valve 9 through the resistance 6 and the battery 7. The resistance 6 and a portion of the battery 7 are short-circuited at the synchronizing frequency by means of a rotary switch 8 coupled to the picture drum. On the receiving side, Fig. 3, the input terminals 12 are in the grid circuit of valve 13, in the anode circuit of which are the battery 16, resistance 15, and recording galvanometer 14. In parallel with the resistance 15 is a filter 17 which accepts the synchronizing frequency and the output of which is applied to the primary of the transformer 18. The output of transformer 18 is applied to the grid of valve 19, in conjunction with the biassing battery 22. The synchronizing impulses are taken from terminals 21 in the anode circuit of valve 9. The negative potential on the grid of valve 9 is arranged to be the greatest, corresponding to the point G1 on the valve characteristic curve, Fig. 4, when no picture impulse is passing and when switch 8 is open. A picture impulse reduces this potential to a value corresponding to G3, while G2 and G4 are potentials caused by the closing of switch 8 when a picture impulse is absent and present respectively. The shaded areas b, s below the curve, Fig. 4, show typical variations of these' voltages with time, s being the synchronizing impulses superimposed on the picture impulses b, while s<1> and s<11> are portions of an impulse s divided by the cessation of the picture impulse. The complete transmission of a picture is of the form shown in Fig. 1. By adjusting the galvanometer 14 the synchronizing impulses, which are of smaller amplitude than the picture impulses, are prevented from affecting the recording of the latter. The shadow F, Fig. 4, of the galvanometer thread normally covers the slit Sp as at a; the slit is only uncovered by a picture impulse as at c, the synchronizing impulse being insufficient alone to uncover the slit, as at b, and in conjunction with the picture, impulse serving merely to increase the distance of the shadow from the already uncovered slit, as at d. The synchronizing frequency may thus be greater or less than the highest picture frequency.