US1813923A - Radio receiving system - Google Patents

Description

July 14, 1931. R A, H I G- 1,813,923

RADIO RECEIVING SYSTEI Filed Feb. 6. 1929 F76. I-A

/Nl ENT0R R A. HE/S/NG Arm/w Patented July 14, 1931 UNITED STATES PATENT OFFICE RAYMOND A. HEISING, F MILLIBURN, NEW JERSEY, ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW "YORK, N. Y., A CORPORATION OF NEW YORK Application filed February This invention relates to radio receiving systems and more particularly to a methodand means whereby a locally generated wave- I e carefully shielded from each other, etc.

16 Still other difiiculties are experienced when short waves are to be received by the 'heterod ne'method. Probably the most serious 0 these difiiculties is that due to the coupling between the antenna circuit and the local oscillator circuit, which should be tuned to fre uencies that are relatively close to each ot er, a change in the tuning of either circuit is likely to change the tuning of the other circuit. Correct tuning which is very 95 important is therefore very diflicult.

Another difiiculty is that the locally suplied oscillations, which differ in frequency y but a slight amount from the frequency of the waves which it is desired to receive, are

fed into the antenna system and are radiated. To overcome the difliculties noted it has been proposed to use combining oscillations having a frequency which differs bya slight amount from one-half the frequency of the oscillations produced b the incoming waves. However, the amplitu e of the intermediate frequency current produced by the combining action is much smaller than that resulting when the two oscillations are of substantially the same frequency. ,This isdue to the fact. that the locally suppliedoscillations are effective in producing an intermediate frequency wave during less than one-half of.

each cycle of the local oscillations.

To offset the decreasein amplitude of the intermediate current, increased amplification of the radiofrequency or intermediate frequency current -has"beifresorted tofbut with unsatisfactory results. 7

The presentinvention has as its main ob- RADIO RECEIVING- sYs'rEm e, 1929. s rial No. 337,785.

ject the provision of means for combining incoming waves with locally enerated oscillations of approximately one alf the incom- -ing wave frequenc in such manner that the resultant interme iate frequency wave will,

oscillations and the incoming wave are 180 out of phase with each other, but which is not present when these waves are in phase, whereby the amplitude of the intermediate frequency wave is increased.

An incidental advantage resulting from the use of local oscillations of approximately one-half the frequency of the incoming wave is'that it becomes unnecessary to balance the first detector.

' Other objects and features will be evident and the, invention better understood from the following description together with the attached drawings in which Figs. 1A and 1B illustrate graphically the relation existing between an incomng wave and the locally generated wave when the phase of the incoming wave has been changed through 180;

Fig. 2 illustrates graphically the conditions of Figs. 1A and 1B superposed to fa cilitate comparison;

Fig. 3 illustrates schematically the application of the invention to a radio receiving system, while Figs. 4, 5' and 6-are schematics of modifications of the circuit of Fig. 3.

Referring particularly to Fig.11-A the curve W represents the incoming wave, curve 0 represents the wave generated by a local sourcewhich' has a frequency differing but slightly from one-half the frequency of the incoming wave. I

As illustrated, waves 0 and W are in phase, and when they are combined one component of the resultant is represented by curve F. When waves 0 and W are in phase the desired intermediate frequency component F has an amplitude greater than that of the locally generated wave.

In Fig. 1B curves W, O and F represent the incomin wave, the locally generated wave and t e desired intermediate frequency component, respectively. Wave W is 180 out of phase with the wave supplied by the local source and as a result the wave F has an amplitude smaller than that of the locally generated wave.

As iswell known the average value of avariable quantity during a given interval of time may be determined from the graph of the quantity by dividing the area under the graph for that interval by the corresponding value representing the duration of the interval.

It is also well known that when two waves are combined the am litude of the resultant wave is determined y the variation of the average values. More specifically,.the intermediate frequency wave in a heterodyne receiver is the envelope of the average values of the combined waves as they vary from a maximum to a minimum in accordance with the change in phase relation. The amplitude of the intermediate frequency wave depends upon the variation between the average maximum value and the average minimum value, from which it follows that if the average minimum value can be decreased without decreasing the average maximum value to the 'same extent, the amplitude of the intermediate frequency wave will be increased.

The manner in which the average minimum value of a combined wave may be decreased without a corresponding decrease in the average maximum value, in accordance with the present invention, is shown in Fig. 2. W and W represent the incoming wave at phases 180 apart (Figs. l-A and B superposed), 0 represents the locally generated wave. and F and F represent the intermediate frequency components corresponding to W and W, respectively;

Reading the fore oing statements'in terms of Fig. 2, the amplitude of the intermediate frequency component depends upon the difference in area under the graphs F and F. Of these areas, that portion designated by points 1, 2, 5, 4 is common" to both F and F, but the portions 1, 4, 3 and 2, 5, 6 are in the area under graph F and not under F. Since F represents the minimum, if the areas 1, 4, 3 and 2, 5, 6 can be eliminated, the minimum will be decreased without affecting the maximum.

Line 7, 8 represents the zero or reference line and waves W, W and O are illustrated as varying to either side of this line an equal amount. If now the reference line can be moved without changing the absolute'positions of the graphs (or waves) certain of the areas noted can be eliminated. For instance, if line 9, 10 be drawn through points 1, 2 and the curves and areas under line 9, 10 made ineffective, the minimum area will have been reducedto a greater extent. than the maximum area, or the intermediate frequency amplitude will have been increased.

In Fig. 3 a method of transferring the reference line 7 8 to position 9, 10 is indi cated. In this figure an antenna 11 is tuned to receive a wave of frequency f The receiving circuit, containing rectifier or .detector 13 and source of oscillations 14, is coupled to the antenna circuit by transformer 12. Source 14 is adapted to generate oscillations differing a small amount from onehalf the frequency of the incoming wave, that is, a frequency may be amplified, etc; as is common practice in heterodyne receivers.

Fig. 4 illustrates a receiving circuit in which the rectifying or detecting device is represented as a space discharge device 17. In this case the negative potential is impressed upon the grid of device 17 to accomplish the desired result.

In Fig. 5 the negative potential source 15 is arranged to impress its potential on the grid of device 17, while the locally generated wave isimpressed upon the plate of device 17. This arrangement, as will be readily understood by those skilled in the art, gives the same result as with the arrangements of Figs. 3 and 4.

The amplitude of the intermediate frequency component obtained by using the arrangements of Figs. 3, 4 and 5 is still not as large as that which would be obtained if the locally generated wave were of a frequency I more nearly equal to that of the incoming wave. However, the amplitude may be increased by increasing the plate voltage applied to device 17 in Figs. 4 and 5 and at the sametime adjusting the negative voltage applied to the grid by source 15.

A further method of increasing the amplitude is shown schematically in Fig. 6.

" Here the incoming wave of frequency f is impressed upon coil 18 included in the input circuits of two space discharge detectors 19 and 20. The input wave is impressed upon the grids of detectors 19 and 20 1n parallel.

The output circuits of detectors 19 and 20 are arranged in such a manner that alternate half waves of the oscillations, having a frequency of f supplied by source 14 are applied to the detectors 19 and 20. In this arrangement both half cycles of the locally generated wave are utilized instead of but one-half of this wave as is the case with the arrangements of Figs. 3, 4 and 5. Since more of the incoming energy is utilized, the amplitude of the intermediate frequency component is increased and the system becomes more efiicient.

In connection with the arrangements of Figs. 5 and 6, if the amplitude of the locally generated wave is sufficiently large, the direct current voltage source for the plates of the space discharge devices will not be necessary. This is illustrated in Fig. 6, by the switch 21 which is. adapted to complete the external plate-filament circuit through condenser 23 if desired or through source 22.

It is to be understood that whereas certain embodiments of the invention have been illustrated and described, the invention is not to be so limited but only as defined in the appended claims.

What is claimed is:

1. In a radio receiving system, a receiver for incoming waves, a source of oscillations having a frequency which differs by a small amount from one-half the frequency of the incoming waves, a space discharge device having a control electrode or grid in wh1ch said incoming waves and said oscillations are combined, and means for applying to the grid of said space dischargedevicea negative potential of such value that transmission of the combined wave therethrough is permitted only during portions of alternate half waves of said oscillations.

2. In a radio receiving system, a receiver for incoming waves, a source of oscillations having a frequency which diflters by a small in amount from one half the frequency of the substantial portion of each half cycle of the incoming waves, a pairof space discharge devices each including acontrol electrode or grid in which said incoming waves and said oscillations are combined, means whereby said incoming waves are impressed upon the grids of said devices in parallel, means whereby half waves of said oscillations are alternately impressed upon said devices, and means for impressing on the grids of said devices a negative potential of such value that transmission I of the combined wave through, said devices waves are 180 out of phasethan when said two waves are in phase.

4. The method of heterodyne reception which comprises combining a received signal wave with a heterodyne wave having a frequency differing by a small amount from onehalf the signal wave frequency and producing a current corresponding to the alternate crests of the combined wave.

5. The method of heterodyne vrece tion whichvcomprises combining a received signal wave with a heterodyne wave having afre quency differing by a small amount from one half the signal wave frequency and producing current pulses corresponding to the al-' ternate crests of the combined wave of duration substantially equal to one-half the signal wave period.

6. The method of heterodyne reception which comprises combining a received signal.

wave with a relatively stronger heterodyne wave having a frequency differing by a small amount from a subharmonic of the signal wave frequency and producing current pulses corresponding to the alternate crests of the combined, wave of duration substantially equal to one-half the signal wave period.

7 The method of heterodyne reception which comprises combining a received signal Wave with a. relatively stronger heterodyne wave having a frequency differing by a small amount from a subharmonic of the signal wave frequency, producing periodic current pulses corresponding to the crests of the combined wave of duration substantially equal to one-half the signal wave period and selecting from the impulsive current a component of a desired beat frequency.

8. The method of heterodyne reception which comprises combining a received signal wave with a heterodyne wave having a frequency differing by a small amount from one half the signal wave frequency and suppressthe effect of the combined wave during a heterodyne wave.

9. The method of heterodyne reception which comprises combining a received slgnal wave with a heterodyne wave having a frequency differing by a small amount from a subharmonic of the signal wave frequency and suppressing the effect of the combined wave during a substantial portion of each half cycle of the heterodyne wave.

10. A heterodyne receiving system comprising a receiver for incoming signal waves,

.a source of heterodyne oscillations having a frequency which differs by a small amount from one-half the signal wave frequency means for combining the incoming signal waves withv the heterod ne oscillations and means for suppressing t e efiect of the com- .bined waves during a substantial portion of each half cycle of the heterodyne wave.

11. A heterodyne receiving system comprising a receiver for incoming signal waves,

a source of heterodyne oscillations having a frequency which differs by a small amount from one-half the signal wave frequency, means for combining theincoming signal waves with the heterodyne oscillations and means for producing periodic current ulses corresponding to the crests of the com ined wave of duration substantially equal to onehalf the signal wave period.

12. A heterodyne receiving system comprising a receiver for incoming signal Waves, a source of heterodyne oscillations adjusted to-a frequency differing by a small amount from half the signal wave frequency, means for combining the incoming signal Waves with the heterodyne oscillations, means for producing periodic current pulses corresponding to the crests of the combined wave of duration substantially equal to one-half the signal wave period, and means for selecting a wave of a desired beat frequency from the said impulsive current. I

In Witness whereof, I hereunto subscribe my name this 31st da of January, 1929.

RA 0ND A. HEISING.

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