US1481945A - Radio receiving system - Google Patents

Description

Jan.

Filed March 1921 Fatented Jan. 29, 1924.

UNITED STATES 1,481,945 PATENT OFFICE.

JUL WEINI BEBGEB, 0! NEW YORK, 11. Y., ABSIGNOB. TO RADIO CORPORATION OF AMERICA, A CORPORATION 01 DELAWARE RADIO RECEIVING SYSTEM.

Application fled larch a, 1921. Serial no. 449,489.

To all whom it may concern:

Be it known that I, Junros Wmmmnena, a citizen of the United States, residing in the boron h of Manhattan, city, county, and State of ew York, have invented certain new and useful Improvements in Radio Beceivin Systems, 0 which the following is a specification.

This invention relates to radio communication and aims to provide means for eliminating interference.

Since all electromagnetic waves reaching a receiving antenna produce an effect to a greater or less extent, it is necessary to adopt means foreliminating or reducing the efiec'ts of all waves but the ones proceeding from the desired-sending station. Various means have been proposed for this purpose, the most common probably involving the tuning of the antennae and receiving circuits to the wave length to be received. This is more or less successful. when the desired wave and the interfering waves are of the.

same order of strength and of widely different frequencies, but it is of little use when the interfering waves are much stronger than the desired waves and of nearly the same frequency. Interference of this nature .is encountered when the receiving station is near to an interfering transmittm station as compared to its distance from t e transmitting station being received.

The aim of my invention is to overcome relatively strong interference of this kind, though it may be used for the prevention of interference regardless of the strength of the interfering current.

The invention can be applied in various ways but I have shown by way of example illustrative embodiments on the accompanying drawings in which:

Fig. 1 represents diagrammatically a. receivin system and Fig. 2 is a modi cation thereo Referring to the drawing, 1 represents an antenna, and 2 a receiving circuit tuned to the signal frequency. The receiving circuit comprises the usual coupling coil 3 loading coil 4 and tuning condenser 5 coupled to an ordinary detector circuit 6- comprising an inductance 7 and tuning condenser 8, by means of variable coupling coils 9, 10. The coupling coils are both connected at one end to a condenser 11, the other slde of which is connected to the receiving and amphfier' circuit. In order to eliminate an interfering signal of a frequency f the mutual inductance M between the coup coils 9, 10 and the capacit C of the con enser 11 is so chosen or justed that the relation between these values is represented substantially by" the. following equation:

The modification shown in Fig. 2 differs from Fig. 1 in that the receiving circuits are somewhat simplified by eliminating the circult 3, 4, 5 and coupling the antenna coil 12 directly to the detector circuit. The relation of the mutual inductance between coils 12 and 10 and the capacity of con-- The voltage e generated in coil 10 by current '21 passing through coil 9 due to the mutual inductance M between the coils is given by the expression:

Now if it is desired to have zero voltage across the circuit 10, 11 for the frequency f, the necessary condition is that -e .:e or

i Z'I'fM't m which reduces to.

Therefore if it is desired to eliminate an interfering frequency of f this can be done by choosing or adjusting the mutual inductance and capacity in accordance with equation (1).

However,

when this is done the voltagesllo across inductance 10 and condenser 11 will not be equal for the signal frequency, and the amplifier circuit will respond thereto.

The equations given above are based on inating interference, comprising primary and secondary circuits, a pair of connections acros the primary and secondary c1rcu1ts, each connection comprising two portions consisting of capacity and inductance in series, one of said portions being common to both connections and the other portions being arranged to couple the primary and seconda circuits, said portions being relatively a justable to substantially eliminate interference.

2. In radio telegraphy, means for eliminating interference, comprising primary and secondary circuits, adjustable coupling coils for varying the coupling between the primary and, secondar circuits and a condenser in series with both of the cou ling coils and connected to the primary and secondary circuits, the mutual inductance of said coupling coils and the ca acit of said condenser being relativel ad uSte to substantially eliminate interference.

3- In radio telegraphy, means for elim inatin interference comprising primary and secon ary circuits, coupling coils between the primary and secondary circuits and a condenser in series with both of the coils and connected to the primary and secondary circuits, the mutual inductance between the coils and the capacity of the condenser being adjusted so that their relation is substantially expressed by the equation stantially eliminate interference on the secondary circuit.

5. In radio signaling apparatus having a primary and a secondary circuit, a coupling coil havin one winding connected in said primary circuit, and another winding connected in said secondary circuit, a variable capacity in series with both said windings, and means for varying the coupling between said windings.

JULIUS WEIN BERGER.

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