Patent GB-416707-A (GB)
Title: Improvements in or relating to modulated carrier wave transmitting apparatus
IPC: H03C3/26
Filed: 1933-09-15
Abstract: 416,707. Wireless transmitting systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Usselman, G. L. ; Port Jefferson, Long Island, New York, U.S.A.) Sept. 15, 1933, Nos. 25638 and 25639. Convention dates, Sept. 30, 1932 and Oct. 15, 1932. [Class 40 (v).] A frequency or phase modulated carrier wave transmitter comprises a high-frequency source connected to a mixing valve over two parallel branches of a coupling circuit, said branches having means for relatively shifting the phase of the oscillations, and the effective conductivity of the branches being oppositely varied by the modulating potentials. In the arrangement shown in Fig. 1, an oscillator A, e.g. a crystal or long line frequency controlled oscillator, is connected to a phase splitting circuit PS, one branch of which comprises a phase retarder 2 and resistance 4 while the other branch comprises a phase advancer 3 and resistance 5. The oscillations from PS pass to the control grid of a screened grid mixing valve Z and thence to a frequency multiplier, limiter or ordinary amplifier D. The branches of the phase splitting circuit are shunted respectively by a valve X, Y, the grids of which are connected through parasitic, preventing resistances 14, 15 and in phase opposition to a signal source B. The plate, filament, screen and bias potentials are derived in obvious manner from a battery or other source 21 and potentiometers P1. P2. In the absence of signals, the output of PS comprises the resultant of two waves of equal energy, one of which is phase retarded and the other phase advanced by equal angles so that the phase angle of the resultant is constant. Signals from B vary the impedances of valves X, Y in phase opposition so that the energy passed by the two branches of PS is varied accordingly, whereby the phase angle of the resultant varies in accordance with the frequency and intensity of the signal. As the phase splitting and modulating circuits present a low impedance to valve Z, matching may be improved by connecting the output of PS to a tapping on the induction element of a tuned circuit connected across the input to Z. The valve Z may be operated as an amplifier or frequency multiplier, in which case the anode circuit CI is tuned to the carrier frequency or a multiple thereof. In the modification shown in Fig. 3, the source A is connected in parallel to the control grids of valves G, H, the tuned output circuits M, N of which are connected over a phase retarder L and advancer Q to the grid of mixing valve V. Signals from B pass to the grids of G, H in phase opposition and each valve operates as an amplitude modulator so that the amplitudes of the waves passing through the retarder L and advancer Q vary in opposition, the resultant output from valve V being a wave of constant amplitude having a phase angle varying according to the frequency and intensity of the signals. Frequency multiplying and amplitude limiting devices previously mentioned may be used in this modification, and the valves G, H may also operate as frequency multipliers. The tank circuits M, N may be loosely coupled. The modulating signals may be applied to the screen grids instead of to the control grids, Fig. 4 (not shown), or to the anode circuits, Fig. 5 (not shown). Three electrode valves may be used, and in the arrangement described with reference to Fig. 6 (not shown), the amplitude modulators G, H are neutralized triodes, the neutralizing capacities being connected between the grids and one of the ends of centre tapped tuned anode coils. The neutralizing capacities may be adjusted to give slight feed-back. In a further modification, Fig. 7, the impedance of the source A is matched to the input circuit impedance of valves G, H by tapped connections to a tuned input inductance 440. The arrangement shown results in the carrier being applied to the valves in counterphase and in order that the outputs connected to the phase shifting elements L, Q may be in phase, the anode circuit connections of valve H are the reverse of those of valve G. In this case, neutralization is effected by capacities NC, N<1>C<1> between the anode of one valve and the grid of the other. Specification 411,638 is referred to.