GB445668A - Improvements in or relating to high frequency telegraph transmitters - Google Patents

Abstract

445,668. Wireless transmitting-circuits. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE, 12, Hallesches Ufer, Berlin. Aug. 1, 1935, No. 21877. Convention date, Aug. 4, 1934. [Class 40 (v)] In a radio telegraph transmitter employing a drive oscillator and one or more amplifying stages, and in which key clicks are avoided by gradual or delayed keying of an amplifying stage, keying of the drive oscillator is effected automatically in dependence on the aerial current. When tone modulation is employed, the amplitude of the tone frequency is varied in dependence on the aerial current. As shown in Fig. 1, the key T operates through a delay device 2 on the grid circuit of the amplifier 1, giving a gradual rise and fall of aerial current as the key is closed and opened respectively. When the key T is closed, the contact of a relay I falls back and starts the generator 3. As the aerial current rises, a rectifier 5 in a circuit coupled to the aerial, or otherwise associated with the output of the valve 1, energizes a relay II, which closes its contact and maintains the oscillator in action until the aerial current has died away. The relay II may be fitted with a delay winding, or the time constant of its circuit may be chosen to give a suitable delay. The relays I, II may be combined by a single relay with two windings, or they may be replaced by valves. Fig. 3 shows a circuit adapted for tone-frequency modulation. The tone is genorated by a valve 7 and amplified by a valve 8 the output of which is coupled into the grid circuit of the transmitting-amplifier 1, the output of which is thereby modulated. To prevent full modulation voltage being applied during the rise and fall of aerial current, a rectifier 5 in a circuit coupled to the aerial has its load resistance connected in the grid circuit of the valve 8 causing a reduction of the tone-frequency amplitude during the rise and fall periods. The systems of Figs. 1 and 3 may be combined in the same transmitter, and the same rectifier 5 may be used for the keying control and the tone control.