US1955245A - Radio receiving system - Google Patents

Description

April 17, 1934. N. E. LINDENBLAD 5 RAD IO RECEIVING SYSTEM Filed March 23, 1928 II 16 v 14 L 10 PHI/YR 24 14 I n- I 10 E E RECi/Vtk I i l INVENTOR NlLS E. UNDENBLAD RY ATT NEY Patented Apr. 17, 1934 UNITED STATES 1,955,245 RADIO. RECEIVING SYSTEM Nils E. Lindenblad, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March 2 3, 1928, Serial No. 264,130 2 Claims. (01. ZED-20) '10 damped, and also modulated carrier energy, for

the latter is substantially undamped, relative to the high damping of strays. It is an object of my invention to reduce stray disturbances by providing circuits which will discriminate between undamped and highly damped energy impulses.

Incidentally, such an arrangement aids in preventing interference by code signals from spark transmitters, which are especially bothersome owing to their wide frequency band.

Stray disturbances can never be successfully reduced by using tuned. circuits alone, because no matter what the arrangement is, as soon as the disturbance has entered a tuned circuit it sets up an oscillation, and will stay there until it is able to pass on to other circuits coupled to it, or is absorbed by the resistance of the first circuit, for each disturbance represents a certain amount of energy which must be dissipated before it will disappear. It has been suggested to use resistances in the receiving circuit to aid in the dissipation of the disturbance, but the use of simple resistances alone does not change the signal to stray ratio, while the use of resistances in tuned circuits handicaps the reception of the desired signal, and permits disturbances to reach the tuned circuits, where their effect may be noticed perhaps long after the stray has entirely passed by the receiving station.

The object of my invention is to reduce stray 4o disturbance by discriminating between undamped ranged in series with an absorption resistance of the order of magnitude of the impedance of the tuned circuit for energy of the resonant frequency. The inert circuit is coupled in series with an aperiodic antenna, so that the impulses applied to it are a true copy of the electrical waves in space, and the receiver is coupled, to the resonant circuit of the electrically inert circuit. In this way most of the initially received energy is absorbed in the resistance, but the remainder is efiiciently resonated, so that undamped synchronous energy is built up. 7

The invention is more fully described in the following specification, which is accompanied by a drawing in which Figure 1 indicates my invention as applied to a wave antenna, which is most desirable; and

Figure 2 shows its application to an aperiodic loop antenna.

Referring to Figure 1 there is a wave antenna 2 grounded through a surve resistance 4, and coupled to an electrically inert-circuit 6 through an intermediate coupling tube 8. The coupling tube serves to block the inert circuit and receiver circuits from the wave antenna, so that the latter may be kept practically perfectly aperiodic.

The inert circuit 6 comprises a parallel resonant circuit 10, which is tuned to the desired signal, and an absorption resistance 12, which is preferably of the order of magnitude of the parallel impedance of the circuit 10 to energy of resonant frequency. 1

The receiver 14 is suitably coupled to the tuned circuit 10. In the present case the connection is made through the medium of another coupling tube 16, the grid of which is blocked from the p high potential on the anode of the tube 8' by means of a blocking condenser 18, and the bias of which is established by means of a grid leak resistance 20.

When subjected to a sudden impulse the action of the inert circuit may be explained] as follows. In transient behavior, in series with the high resistance 12, the condenser of the tuned circuit 10 has zero reactance, and the inductance has infinite reactance, and they cannot be brought to equal values for parallel resonance with its resulting high impedance except by the application of sustained oscillations. It follows that for a sudden impulse the impedance of the inert circuit 6 is practically entirely that of the absorption resistance 12, so that the potential applied to the inert circuit is spent practically entirely in the resistance 12, and practically no potential is applied to the grid of the coupling tube 16, for that is coupled below the resistance. However, when sustained oscillations from a continuous wave signal are applied to the system the slight impulses which leak through the resistonce 12 gradually build up in the circuit 10 and cause it to have a high impedance of magnitude comparable with that of the resistance, so that for undamped oscillations a substantial portion of the inert circuit 6 is the impedance of the tuned circuit 10. The potential across this circuit is directly applied to the coupling tube 16, and serves to energize the receiver. In this Way the ratio of response to energy which is highly damped, and to sustained oscillations, is made enormously different. If, on the other hand, a voltage produced in the antenna is applied directly across a tuned circuit without a resistance in series the tuned circuit will respond to even a sudden impulse, because the energy from a sudden impulse charges the condenser, and causes sustained oscillation in the tuned circuit, instead of being dissipated in the resistance.

Figure 2 shows how the inert circuit 6 may be used to couple a receiver 14 to an aperiodic loop 22. The inert circuit is simply placed in series with the untuned loop, and the receiver is coupled to the timed circuit of the inert circuit. In the present case inductive coupling has been shown, and preferably a' grounded ast'atic shield 24 is provided between the coils of the coupling transformer.

Experiments with this inert circuit show that communication may be carried on even through heavy lightning storms which make reception impossible with an ordinary tuned receiver. The reception is best for plain continuous wave signals, and is slightly worse for signals which are somewhat damped, like the modulated carriers of broadcasting stations. Spark reception is efiectively prevented unless the coupling is made very strong.

Even an aperiodic loop is somewhat reactive and will store some energy, but a wave antenna is ideally combined with my inert circuit, for it is non-reactive, owing to its surge resistance termination, and therefore possesses no electrical inertia.

I claim:

1. In receiving apparatus, a wave antenna, a resistance connected between one terminal of said antenna and ground, a thermionic repeater having anode cathode and grid electrodes, means for connecting said cathode and grid electrodes to the terminals of said resistance, an inductance and variable capacity connected through a resistance to said anode, a second thermionic tube having its grid electrode connected through a capacity to the connection between said resistance and said inductance, and indicating means connected with the output electrodes of said last named tube.

2. Receiving apparatus comprising a wave antenna, a surge resistance connected between said antenna and ground, a thermionic coupling tube having its control grid connected to one terminal of said resistance and its cathode connected to ground, an absorption resistance connected to the anode of said tube. an efficient parallel resonant circuit having one terminal connected to said resistance and the other terminal connected by way of a capacity to the cathode of said tube, a receiver, and'a thermionic repeater having its output electrodes connected with said receiver and its control grid electrode connected to the terminal of said parallel resonant circuit, which is connected to said absorption resistance.

NILS E. LINDENBLAD.

Images