Patent GB-194070-A (GB)
Title: Improvements in and relating to high-frequency telephony systems
IPC: H04B1/46
Filed: 1922-01-14
Abstract: 194,070. Pollock, E. Jan. 14, 1922. Combined transmitting and receiving arrangements; thermionic valves, arrangements and connections of; thermionic modulating systems and apparatus.-A combined transmitting and receiving set is so arranged that the receiving circuits are rendered insensitive during the period when transmission is taking place, thermionic tubes energized by the microphonic current being variously employed to achieve this result. In certain cases, radiation from the transmitting-aerial can only occur when, and for as long as, the microphone is being spoken into. As shown in Fig. 1, the transmitting-aerial q is energized by a thermionic generator g. The transmitted energy is modulated into speech form by an absorption triode a, the conductivity of which is controlled by the microphone currents through a transformer p, s. The receiving- aerial q<2> is coupled to a detecting-triode b, the high-tension supply e<2> of which is shunted by a diode k, which is normally non-conductive. So long, however, as speech current variations occur in the microphone circuit m, e, p, p<2>, the filament of the diode k will be energized, and the high-tension supply e<2> will be short-circuited so as to render the receiver b insensitive. In Fig. 3, the microphone current is amplified by a triode o placed in shunt across the primary coils p, p' and p<3>, p<2>. The high-tension supply h to the thermionic generator feeding the transmitting-aerial q can only pass through an interposed diode n when this is energized by the amplified microphone currents through the transformer s<6>, p<5>. A pair of diodes f, d are shunted across the receiving-aerial q<2>, and a triode j shunts the plate battery of the detecting- valve b. These three tubes are all rendered conductive through the coils p<3>, s<4>, s<3>, and p<2>, s<2> respectively, and act conjointly to divert any power picked up by the aerial q<2> and so prevent it from affecting the receiving phones t. Instead of two separate aerials, one may serve both for reception and transmission, the aerial inductance linked to the receiving-device being short-circuited in a similar manner so long as transmission is actually taking place. In Fig. 6. the transmitting-aerial q is energized by a high-frequency alternator g. A low-frequency alternator w feeding the filament of the receiving triode b is shunted by a pair of rectifying-diodes y, 2. When the microphone m is being spoken into, the energy from the alternator w is bypassed through the rectifiers, and the receiving tube b is thereby rendered inoperative. In Fig. 8, both the plate and filament circuits of the receiving-tube b are normally fed through a transformer p<2>, s<5>, s<2> from the alternator w, a rectifier n<2> being interposed in the plate supply. When the microphone is being used, the coil p<2> is short-circuited, and the energy so by-passed is fed through a transformer p<11>, s<11> and diode n to the plate of the thermionic generator g supplying the transmitting aerial q. Specifications 194,765 and 194,836 are referred to.