Patent GB-945685-A (GB)
Title: Improvements in radio receivers more particularly for multiplex pulse signals
IPC: H04J3/04
Filed: 1960-06-20
Abstract: 945,685. Valve amplifying, frequency changing and supply circuits; valve pulse circuits; multiplex pulse code signalling. PRECISION MECANIQUE LABINAL. June 20, 1960 [June 22, 1959], No. 21596/60. Headings H3F, H3P, H3W and H4L. [Also in Division G4] A receiver for multiplex signals in the form of coded pulses (see Division G4) comprises a pentode R.F. amplifier V101, Fig. 2, with cathode bias, the anode of which is resistancecapacity coupled to the primary of a wide band transformer T101. The secondary of this transformer feeds into the grid of one element V1022 of a double triode operating as a mixer, being suitably biased by a resistor R105 in its cathode circuit. The other element V1021 of the double triode acts as local oscillator, tuned circuit L104, C105 being connected between its anode and grid; it feeds the mixer V1022 via resistance-capacity coupling R103, C107 and a tap on the secondary of transformer T101. The mixer is followed by I.F. stages V103- V105, the first two of which feed into tuned circuits comprising variable inductors L110, L113 in the anode circuits. The final I.F. stage V105 is resistance-capacity coupled to a tuned circuit comprising variable inductor L116 and feeds into diode rectifier D101. The anode supply is decoupled by means of chokes, e.g. L102 and capacitors, e.g. C102 while the heater supply is similarly decoupled, by means of chokes, e.g. L103 and capacitors, e.g. C103. Channel separator (valves V140-V145, Fig. 3) and command channel (valves V146-V150, Fig. 3) circuits. Positive-going demodulated pulses from a decoding circuit are applied over condenser C143 to the grid of valve V140 in monostable state pair V140, V141, in which valve V140 is normally non-conductive and V141 conductive. On arrival of each synchronizing pulse the circuit reverses state for a period slightly longer than the interval separating the channel pulse furthest from the synchronizing signal from this latter signal itself. During this period tuned circuit C145, T111 rings, its tuning frequency being such that a sinusoidal waveform is produced which passes through zero in a positive-going direction at points corresponding to every signal channel period. In a modification (Fig. 4, not shown), the tuned circuit is fed from a separate valve. The sinusoidal waveform is reversed in phase by the transformer T111, and passed over condenser C146 to the grid of valve V142 in the two stable state pairs V142, V143 in which valve V142 is normally conductive and V143 non-conductive. At every instant when the sinusoidal waveform at the grid of valve V142 commences to go negative the pair reverse state, returning to their original state at the points at which the sinusoidal waveform commences to go positive. The resulting positive-going rectangular pulses at the anode of valve V142 are differentiated by differentiating circuit C148, R156 and the resulting pulses applied to the grid of valve V144. This valve has its anode-cathode path connected in parallel with that of a blocking oscillator V145, both valves being normally biased non- conductive by means of potentiometer R157, R171; each positive-going pulse produced by differentiation from the leading edge of a rectangular pulse renders valve V144 conductive. A pulse of current then passes into transformer T112 which releases the blocking oscillator, so that the latter produces a corresponding pulse at low impedance. The pulses derived from valve V145 are used to open a number of " command channels " each of which comprises a pulse counting circuit including a series condenser C151a &c. In the single " command channel" shown, the series condenser C151a charges a further condenser C152 stepwise via diode CX144; condenser C152 is so chosen that the number of pulses appropriate to the channel concerned charges it to a potential which renders operative a normally biased backblocking oscillator V146. Condenser C152 discharges relatively slowly over resistor B165. The channel gating pulses which appear at the anode of valve V146 are applied to a further valve V147, which is provided in those cases where although the channels are equally spaced from one another, they are spaced a relatively longer time from the synchronizing pulses. Valve 147 is normally biased conductive. Negative-going pulses from the anode of valve V146 are passed over diode CX145 to discharge a normally charged condenser C154; this puts negative-going pulses on the grid of valve V147, via condenser C156, which cause it to become cut-off. Rectangular positivegoing pulses appear on its anode, the duration of which is determined by the rate of recharge of condenser C154 over resistor R169. A diode CX146 prevents the grid of valve V147 going negative. These rectangular pulses are applied as gating pulses to the innner grid of a gate valve V148, the outer grid of which is fed with the signal from the decoder circuits; the valve is normally biased non-conductive and it only conducts when pulses are present on both grids. Negative-going separated channel pulses from the anode of gate valve V148 pass over diode CX147 to the grid of valve V149 in a bi-stable state pair V149, V150 which is so biased that valve V149 is normally conductive and V150 non-conductive. The presence of a pulse in the signal channel causes the pair to reverse state, the time-constant provided by condenser C161 and resistor R181 being such that the reversal of state is maintained between successive signal pulses, but return to the normal state is made if a signal pulse is absent. The valves V149, V150 operate relay coils R1, R2.