US1951532A

US1951532A - Radio receiving system

Info

Publication number: US1951532A
Application number: US406756A
Authority: US
Inventors: Arthur A Schoen; Arthur A Blyth
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1929-11-13
Filing date: 1929-11-13
Publication date: 1934-03-20
Anticipated expiration: 1951-03-20

Description

March 20, 1934. A. A. SCHOEN Er AL RADIO RECEIVING SYSTEM Filed Nov. 13, 1929 INF INVENTORS M. scnoeu m BY NW.

ATTORN EY Cal Patented Mar. 20, 1934 UNITED STATES PATENT oFicE Blyth, Brooklyn, N. Y.

, assignors to Radio Corporation of America, a corporation of Delaware Application November 13, 1929, Serial No. 406,756

18 Claims.

This invention relates to radio reception and has as its prime object the provision of a novel method and means for reducing image frequency response in a superheterodyne receiver.

It often occurs, when utilizing a superheterodyne receiver, that when the local oscillator thereof is tuned to obtain beat frequency energy with a desired station, another station is heard, which, of course, is undesirable. This interference is due to the fact that the undesired station produces the same beat frequency with the local oscillator that the desired station does; and, in the past was avoided by manually tuning the oscillator to another frequency either above or below its former frequency depending upon its former relationship with the desired station. However, to most radio receiver operators, such procedure is highly bothersome as it involves additional careful manipulation of the oscillator tuning dials.

Accordingly, another object of this invention is to provide a superheterodyne receiver wherein the shift in oscillator frequency to reduce image frequency response is accomplished automatically.

In addition, we have found, depending upon 'the location in which the receiver is placed, that image frequency response is present only over a portion of the range of frequencies to which the receiver is responsive. Therefore, if the receiver is taken from one locality to another, the 'range or portion of the scale on which image frequency response occurs, changes both in magnitude and relative angular position; or in other words, in frequency band width and in position on the frequency spectrum.

Hence, to provide an automatic change-over device for shifting oscillator frequency variable in width and position is a further object of this invention.

Briefly, according to a preferred embodiment of our invention, the foregoing objects are carried out by inserting a reactance in the tunable control circuit of the superheterodyne local oscillator by means of a switching arrangement automatically operable during the manipulation of 'the variable element of the tunable circuit which controls the frequency of the local oscillator. As the switching mechanism is in the form of a commutator mounted upon the element varying the frequency of the local oscillator generator, the angular position at which change-over occurs can be readily controlled. By means of a variable contact, the portion or width of the frequency band in which frequency shift is accomplished, is made variable.

The features of this invention which we believe characterize it are pointed out with particularity in the appended claims; however, our invention may best be understood both as to its mode of operation and construction by referring to the accompanying drawing which, of course, is given solely by way of illustration and not by way of limitation.

Referring to it,

Figure 1 is a diagrammatic illustration of a superheterodyne receiver embodying the principles of our invention; V

Figure 2 illustrates a mechanism for providing variable frequency range change-over both in magnitude and position; and,

Figures 3 and 4 indicate alternative means for causing a predetermined frequency shift in an oscillation generator. 7,

Turning to Figure 1, numeral 2 indicates an antenna which may be a loop or any other desired type of antenna feeding energy into an untuned amplifier, comprising preferably a screen grid vacuum tube 4, for the purpose of preventing radiation from subsequent apparatus in the receiver over antenna 2. The output of amplifier 4 is fed into an oscillating detector OD which in turn feeds beat frequency energy into a tuned intermediate frequency amplifier 6 tuned to a constant frequency. The output of the intermediate frequency amplifier 6 is fed into a detector or rectifier 8, rectified, and thence fed if desired, into a relatively low frequency amplifier 10 and thence translated by any suitable means such as a telephone 12. In order to control and vary the frequency of oscillation of the oscillating detector or local generator of oscillations a tunable circuit 14 is provided comprising an inductive reactance 16 and a capacitivereactance 18 the latter having a straight line frequency characteristic and having fixed stator plates 20 and grounded rotor plates 22.

In order to translate signals from a desired station, the rotor plates of the condenser in tunable circuit 14 are varied by means of knob 24 and shaft 26 until the local oscillation generator produces energy of correct frequency to give a beat note frequency with the desired station corresponding to the tuning of intermediate frequency amplifier 6.

As already indicated, over a given range of frefrequency from a frequency higher than the desired station frequency to one below. Over that range of frequencies, by means of the commutator or switching mechanism X, a fixed reactance 28 is connected into circuit with the tunable circuit. Reactance 28 in the embodiment shown is a condenser of fixed value. As the switching arrangement is fixed to the control shaft 26 its action becomes, of course, automatic during the troublesome range where image phenomena occur.

The switching arrangement is shown in greater detail in Figure 2 together with the means for making variable the magnitude and position of the range of frequencies at which change-over occurs. More specifically, the switching or change-over mechanism comprises a disk of insulating material 30 having an insulating hub 32. By means of a set screw 34 the disk and hub can be placed at any desired angular position on shaft 26. In this manner the position in the frequency spectrum at which frequency shift over occurs is readily varied.

Hub 32 carries a metallic commutator segment 36 and disk 30 carries a metallic segment 38. Both segments are connected together by means of a metallic connecting piece 40 contacting with the under surface of segment 38 and thence over one surface of disk 30 to contact with the under surface of segment 36 at 42. Segment 36 is grounded by means of a contacting element 44.

One side of condenser 28 is connected to stator plates of condenser 20 and the other side iscon nected to ground through a contacting member 46 and segment 38 only when member 46 is contacting with segment 38. Contacting element 46 is carried by means of

screw clamps

48, 50 on an insulating support 52 and, accordingly, may be varied in position along segment 38 as shown by the dotted lines. This variation, of course, gives the magnitude or range width at which it is desired that frequency change-over of the oscillator be made.

Another way of causing shift of oscillator frequency, from frequencies above desired stations to that below the stations for reducing image frequency response,'is shown in Figure 3 wherein to the rotor plates 22 of the oscillator condenser,

areas 54 are added so that for a given range the desired shift in frequency takes place.

In the event that it is desired to shift the o."- cillator frequency in the reverse manner, apparatus as shown in Figure 4 may be resorted to Wherein'by means of the cut away portions 56, on

the oscillator rotor condenser plates 22, the

change-over will be from a lower to a higher fre fractional portion only of its range.

1 2. An oscillation generator comprising an electron discharge tube including a tunable input circuit for controlling the frequency thereof, said tunable circuit comprising a fixed inductance and a variable capacity having a straight line frequency characteristic and being continuously variable to alter the frequency of the tunable circuit over a given range, and means for automatically connecting a fixed capacity to said variable capacity over a portion only of its range.

3. In a receiver, a signal amplifier circuit, a local oscillator stage including a tube provided with a tunable input circuit, an amplifier tuned to a predetermined beat frequency, said tunable input circuit including a pair of reactances of opposite sign, means for varying one of said reactances to produce said beat frequency with amplified different signals, and additional means mechanically operative with said varying means, and including a fixed reactance, for producing said beat frequency with a desired signal without image interference.

4. In a superheterodyne receiver, a signal amplifier circuit, including a screen grid tube, a local oscillator stage including a tube provided with a tunable input circuit, an amplifier tuned to a predetermined beat frequency, said tunable input circuit including a pair of reactances of opposite sign, means for varying one of said reactances to produce said beat frequency with amplified different signals, and additional means mechanically operative with said varying means, and including a fixed reactance of the same sign as the variable reactance, for producing said beat frequency with a desired signal without image interference.

5. In a receiver, a signal amplifier circuit, a local oscillator stage including a tube provided with a tunable input circuit, an amplifier tuned to a predetermined beat frequency, said tunable input circuit including a pair of reactances of opposite sign, means for varying one of said reactances to produce said beat frequency with amplified different signals, and additional means mechanically operative with said varying means, and including a fixed capacity, for producing said beat fnequency with a desired signal without image interference.

6. In a receiver, a signal amplifier circuit, a local oscillator stage including a tube provided with a tunable input circuit, an amplifier tuned to a predetermined beat frequency, said tunable input circuit including an inductance and a capacity, means for varying said capacity to produce said beat frequency with amplified different signals, and additional means mechanically operative with said varying means, and including a fixed reactance, for producing said beat frequency with a desired signal without image interference.

'7. In a receiver, a signal amplifier circuit, a local oscillator stage including a tube provided with a tunable input circuit, an amplifier tuned to a predetermined beat frequency, said tunable input circuit including an inductance and a capacity, means for varying said capacity to produce said beat frequency with amplified different signals, and additional means mechanically operative with said varying means, and including a fixed capacity for producing said beat frequency, with a desired signal without image interference.

8. In a superheterodyne receiver, a signal amfier circuit, including a screen grid tube, a local oscillator stage including a tube provided with a tunable input circuit, an amplifier tuned to a predetermined beat frequency, said tunable input circuit including an inductance and a capacity,

means for varying said capacity to produce said beat frequency with amplified different signals. and additional means mechanically and simultaneously operative with said varying means, and including a fixed condensive reactance, for producing said beat frequency with a desired signal without image interference.

9. In a superheterodyne receiver, a signal amplifier circuit, including a screen grid tube, a local oscillator stage including a tube provided with a tunable input circuit, an amplifier tuned to a predetermined beat frequency, said tunable input circuit including an inductance and a capacity, means for varying said capacity to produce said beat frequency with amplified different signals, and additional means mechanically and simultaneously operative with said varying means, and including a fixed capacity for producing said beat frequency with a desired signal without image interference.

10. In a superheterodyne receiver an untuned radio frequency amplifier including a screen grid tube, a local oscillator including an electron discharge tube provided with a tunable input circuit, an intermediate frequency amplifier, said oscillator input circuit including a fixed inductance and a capacity, means for varying said capacity to produce said intermediate frequency with amplified different signals, and additional means mechanically and simultaneously operative with said capacity varying means, and including a fixed reactanoe, for connecting the latter to said capacity to produce said intermediate frequency with a desired signal without image interference.

11. In a superheterodyne receiver an untuned radio frequency amplifier including a screen grid tube, a local oscillator including an electron discharge tube provided with a tunable input circuit, an intermediate frequency amplifier, said oscil- 'lator input circuit including a fixed inductance and a variable capacity having a straight line frequency characteristic, means for varying said capacity to produce said intermediate frequency with amplified different signals, and additional means operative with said capacity varying means, and including a fixed reactance, for connecting the latter to said capacity to produce said intermediate frequency with a desired signal without image interference.

12. In a superheterodyne receiver an untuned radio frequency amplifier including a screen grid tube, a local oscillator including an electron discharge tube provided with a tunable input circuit, an intermediate frequency amplifier, said oscillator input circuit including a fixed inductance and a variable capacity having a straight line frequency characteristic, means for varying said capacity to produce said intermediate frequency with amplified different signals, and additional means operative with said capacity varying means, and including a fixed capacity, for connecting the latter to said capacity to produce said intermediate frequency with a desired signal Without image interference.

13. A local oscillator, adapted for use in conjunction with a source of signals of a desired frequency range and a beat frequency utilization circuit, comprising a tube having a resonant input circuit adapted to be coupled to the source and an output circuit adapted to be coupled to said beat circuit, a variable tuning condenser in said input circuit having a grounded rotor element, a fixed condenser having one side thereof connected to the stator element of the tuning condenser, and grounded means, operative with said rotor element through a portion of said range, adapted to connect the other side of said fixed condenser to said rotor element.

14. A local oscillator, adapted for use in a superheterodyne receiver provided with a signal input circuit and an intermediate frequency amplifier, comprising a tube having a tunable input circuit including a variable condenser for adjusting the oscillator through a range of oscillation frequencies adapted to heterodyne with a desired range of signal frequencies separatedfrom said oscillation frequencies by said intermediate frequency, and means, movable with the variable element of the condenser, for changing the effective capacity of said tunable input circuit through a portion of said oscillation frequency range to shift the oscillation frequency values in said portion to values capable of producing said intermediate frequency with the desired signals but not with undesired signal image frequencies.

15. A local oscillator, adapted for use in a superheterodyne receiver provided with a signal input circuit and an intermediate frequency amplifier, comprising a tube having a tunable input circuit including a variable condenser for adjusting the oscillator through a range of oscillation frequencies adapted to heterodyne with a desired range of signal frequencies separated from said oscillation frequencies by said intermediate frequency, and means, movable with the variable element of the condenser, for increasing the effective capacity of said tunable input circuit through a portion of said oscillation frequency range to shift the oscillation frequency values in said portion to values capable of producing said intermediate frequency with the desired signals but not with undesired signal image frequencies.

16. A local oscillator, adapted for use in a superhetercdyne receiver provided with a signal input circuit and an intermediate frequency amplifier, comprising a tube having a tunable input circuit including a variable condenser for adjusting the oscillator through a range of oscillation frequencies adapted to heterodyne with a desired range of signal frequencies separated from said oscillation frequencies by said intermediate frequency, and means, movable with the variable element of the condenser, for decreasing the effective capacity of said tunable input circuit through a portion of said oscillation frequency range to shift the oscillation frequency values in said portion to values capable of producing said intermediate frequency with the desired signals but not with undesired signal image frequencies.

17. A local oscillator, adapted for use in a superheterodyne receiver provided with a signal input circuit and an intermediate frequency amplifier, comprising a tube having a tunable input circuit including a variable condenser for adjusting the oscillator through a range of oscillation frequencies adapted to heterodyne with a desired range of signal frequencies separated from said oscillation frequencies by said intermediate frequency, and means, movable with the variable element of the condenser, for changing the effective capacity of said tunable input circuit through a portion of said oscillation frequency range to shift the oscillation frequency values in said portion to values capable of producing said intermediate frequency with the desired signals but not with undesired signal image frequencies and additional means for varying the magnitude of said portion and the position thereof in said oscillation frequency range.

18. An oscillation generator comprising an electron discharge tube having a tunable input condenser and means for connecting the other plate of said fixed condenser to the said rotor plates, said means comprising a metallic segment, an insulating disc on which said segment is mounted said disc being loosely mounted on said shaft and means for retaining said disc in any desired angular position on said shaft.

ARTHUR A. SCHOEN. ARTHUR A. BLYTI-Ir