GB505303A - Improvements in or relating to radio and like transmitters - Google Patents

Abstract

505,303. Wireless transmitting-apparatus; inductances ; electric resonators. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. March .14, 1938, No. 7924. Convention date, March 13, 1937. [Classes 40 (iii) and 40 (v)] [Also in Group XXXV] In variably-tunable transmitters in which the tuning adjustment is performed by shortcircuiting a portion of the tank circuit inductance, undesired effects due to distributed capacity of the unused portion of the coil are prevented by suitable screening. The anode inductance of the push-pull amplifier, Fig. 2, is divided into two halves V1, V2, each located in a tubular screen and connected to it at the end remote from the anode. An adjustable connection is provided between the inductance and screen for the purpose of tuning. The load R is connected between the points A and B on the screens and a variable shunt formed by the movable bridge plate P is connected in parallel with it. The plate P is maintained at earth potential by connecting it to the external earthed screen S. In order. to keep the direct-current voltage from the load R the inductance screening may be made as a cylindrical condenser consisting of a ceramic cylinder metallized inside and outside. At higher frequencies the screened inductance may be replaced by short-circuited concentric lines, Fig. 3, each with a movable adjusting base D. The earthed screen S and bridge plate P are arranged as before and the method of feeding an unsymmetrical load is shown. The concentric cable K (through which the load is to be fed) has its outer sheath forked, the two portions being connected parallel to the screens of the concentric lines. The core of the cable passes down one sheath only and at the input end is connected to the other sheath by the connection X. For feeding a concentric cable from two transmitters either in parallel or separately, Fig. 4 (not shown), the "symmetrizing loops" from each transmitter are connected together at their closed ends, from which the feeder cable is continued, and switches are provided for altering the necessary connections. The U-formed parts of Figs. 3 or 4 may be replaced by cables coiled up to form variometers, Fig. 5 (not shown), and sliders are provided between the coiled portion and the straight conductors or screens to permit adjustment.