US1723440A - Radioreceiver - Google Patents

Description

Aug. 6, 1929.

Filed Feb. 16 1923 Sheets-Sheet l 6 g F/Lfl. 1

7 l 1 'l l I 1 I l :6 HM TING #4 RECTIFIER OFF RECTIFIER RELAY IND.

l l I l I F GALV 4 I 1 I 1 J RECT 2351 5 AMP AMP.

l l l l L ,A.F.TUNED AMPLFIER RECTIFIER RELAY on RECORDER wveutoz PHOTO- ELECTRDIC CELL RH. RANGER Patented Aug. 6, 1929.

OFFICE.

* UNITED STATES PATENT RICHARD HOWLAND RANGER, 0F BROOKLYN, NEW YORK, ASSIGNOR TO RADIO COR- PORATION OF AMERICA, A CORPORATION OF DELAWARE. 9

' RADIORECEIVER.

Application filed February 16, 1923. Serial No. 619,359.

This invention relates to radio telegraphy and more particularly to a method and means for eliminating or reducing static or natural interference in the reception of radio signals.

, Numerous arrangements have been suggested and used for this purpose depending for example on selective tuning or balancing out the static in opposed portions. The efficacy of such arrangements depends upon changing the ratio of signal to static or upon securing systems of similar characteristics so that the resulting static wave forms are alike so as to permit their cancellation b opposition. Considerable difficulty has een encountered in making static eliminator's reliable andmore or less trouble is encountered in all methods at certain times.

The object of the present invention is to rovide an improved system which reduces the difliculty in reading signals when static or natural disturbances occur.

The term static used throughout the specification and claims is intended to cover all forms of disturbances such as may be set up by electrounagnetic waves of undesired form striking the receiving antenna and, as a result, troublesome interferingsounds are set up in the receiving apparatus. These sounds have been commonly referred to as static, atmospheric disturbances, strays, or Xs, but applicant intends to use the term static to include all of the above forms.

The natural disturbances or statics appear to he of a heterogeneous character having considerable energy. The resultant currents in the receiving circuit are of a discontinuous nonuniform character and in general the effect upon a receiving circuit is similar to that which wouldbe produced by heterogeneous shock excitation. The signal. waves,

however, produce forced oscillations resulting in currents of a continuous andsubstantially uniform character. The operation of my invention is based on this characteristic difference and to a large extent is independent of the actual amount of the undesired energy. v I

In the methods now used the indicator, such as the final receiver or recorder directly combines the tone or marking of the signal with the noise or marking of the disturbance. As static is discontinuous the en ergy is very effective for producing an indication and the known methods permit it to act in a manner by which it often renders the signals unintelligible.

In accordance with the present invention the energy of the signal is utilized to op erate a limiting cut off and during this signal period the static energy is not integrated and on account of its discontinuous nature ordinarily cannot alter this condition. During the spacing periods, the static due to its interrupted character actuates the indicatorby producing noise in the receiver or a marking period in the recorder and the signal is interpreted from either of the latter. Static on account of its energy will also under some circumstances reach the lim iting cut off value but as it is usually of short duration it cannot of itself produce silence in the receiver or a non-marking pe r'iod and for the same reason during the spacing period it will produce noise or a marking period even if it momentarily opcrates the limiting cut off.

As static may not always give sufficient noise to enable the signal to be read I find it advantageous to produce a continuous tone in the receiver and to silence this tone by the received signal energy. Static may convert a portion of the tone into noise, but ordinarily will not entirely silence the receiver.

It will be seen that this method of operation reverses the spaces andindicating periods and would be difiicult for a Morse operator to read. This may be obviated by any suitable reversal such as reverse Morse signalling or by reversing the relays of the recorder when thelatter is used.

In carrying out my invention I utilize an arrangement for cutting off the indicator whenever the received current is greater than a certain limiting valve which is substantially the value of the signal current. I may also utilize an arrangement which also cuts off the indicator when the received current is less than a certain value. The reading signal is only produced when the received energy falls within this band.

The novel features which I believe to be characteristic of my invention are particularly set forth in the appended claims. The invention itself, however, both as to its construction and mode of operation, to-

' traced by a ray of light froni'the recor nection with the accompanying drawings in which Fig. 1 is a diagrammatic view of apparatus illustrating the principle of my in vention,

Fig. 2 shows my invention utilising a particular form of limiting cut oil,

Fig. 3 is a curve showing the galvanometer mirror,

Figs. 4 and 5 show a modification invention utilizing a different type 0 iting cut off, and v Fig. 6 is a curve explaining the operation of this form of limiting cut ell.

In Fig. 1, which is intended to illustrate the principle of, as well as a system in accordance with the invention, 1 is a receiving antenna grounded at 2 and coupled' to a resonant circuit 3, 4: by means of coupling coil 5. For receiving continuous waves a source of alternating current 6 is utilized for modulating the received energy at an audible frequency or for beat reception for example. The received currents, which may if desired be passed through radio or audio frequency amplifiers, are then recti fled. The rectified currents are then impressed on a current interrupter or limiting cut off relay which is adjusted so that when current of the magnitude of the normal signal current is impressed thereon the in terrupter opens the next circuit. Various arrangements have been utilized for accomplishing this result, several of which will be more specifically referred to in connection with the arrangements hereafter described.

' Whenever the current furnished to the limiting cut oil is less than the normal received signal currents or less than a certain minimum value, the relay is closed and the currents supplied thereto are impressed on the transformer 7, and are there rectified and used to operate an indicator, such as a recorder or telephone. If no static is received the indicator will respond to the spaces between the dots and dashes. This may be corrected when necessary by a suit able reversal, such as reversing the transmitter or the relay connected to the indicator.

, hen static is received with the signal currents these added currents cannot, except. under extraordinary conditions 'decrease the signal current below the limiting cut off value and the indication given by the signalling currents during these periods is seldom affected.

During the intervening periods when no signal currents are impressed on the limiting cut off, the static received will not opercurrents.

ate the limiting cut off unless it is of the ma 'nitude of the signalling current. When it is of the magnitude of the signalling current and of short duration, the limiting cut off relay will be operated and the indicator may be nic-mentraily cut off but as the duration is usually very short as compared with a dt or a dash this can ordinarly be distinguished from the effects of signalling As the indications during nonsignalling periods will not be sufiiciently continuous for easy reading unless there is considerable static, I preferably introduce a continuous audible tone in the system, so that during the intervening periods when signal currents are not received to operate the limiting cut off, a continuous tone more or less interrupted by the static noises will be heard instead of the static noises alone. This made he done for example by means of an audio frequency chopper 8 coupled to the antenna; or'in any other suitable manner.

When exceptional static of a duration ate a dot or a dash and of de the signal current is received during intervening periods between the sigrwill operate the cut off and cause the same eifcct as a signal, but it will be noted that is not integrated and cannot, enceptunder extraordinary conditions, affect the: nmi'marking given by the signalling currents.

Fig. 2 shows an arrangement embodying several additional features as well as a particular type of lim ting cut off relay which does not integrate the static energy. The arran ement comprises a radio frequency amplifier,preferably a three electrode vac uum tube connected to the resonant circuit. The modulation frequency supplied is preferably a frequency such as will give a 3,000 cycle beat for example, which frequency is doubled by passing the radio frequency through a double or balanced rectifier 16 and l7. The rectified currents of a pulsation fre quency of 6,000 are then amplified by means of a suitable audio frequency amplifier and the output is impressed on the impulse balance or balanced rectifier which in itself is a device for reducing the effects of static. This arrangement, which is more particularly described in my copending application Serial llo. 581,350 comprises two three-electrode tubes lG and 17 having the grids connected to opposite ends of the secondary of transformer 18 through grid condensers 19 and 20 shunted by grid leaks 21 and 22. The middle point of the secondary is connected to the cathode of the tubes and the plates are connected together and to the filament through the plate battery 23 and the coil 2+1. This arrangement serves substantially to balance the initial impulses, but received currents cumulatively decre'asethe output of when no signal is received.

both tubes, so that the large initial impulses of highly damped static are substantially balanced, as well as the small initial impulses of signals. The sustained impulses, however, gradually increase the negative charge on each of the grids so that the re sultant plate current decreases when a sustained alternating current is impressed on the grids, but a 6,000 cycle variation occurs in the plate current. This super-audio pulsation of 6,000 is impressed by means of a coupling coil 26 upon a galvanometer 25, which may conveniently be of the type used in the well known oscillograph and be re sponsive to frequencies as high as 6,000 and thus possess sufficient flexibility to follow the impulses impressed upon it and the deflection may occur at a high frequency or as a sin gle deflection according to the arrangement of the circuit. In addition, it is desirable to impress an audible frequency of 1,000 on the system preferabl by means of a light 27 placed to shine on t 1e galvanometer mirror, which light is interrupted by any suitable means, such as a rotating shutter 28, at the desired frequency. The mirror of the galvanometer receives and reflects light on a photo-electric cell when the deflection of the mirror is such that the light is reflected on the aperture of the cell. In this modification the galvanometer and the photo-electric cell constitute the non-integrating limiting cut off relay. The recording galvanometer of this type is particularly described in the patent applications of O. A. Hoxey, Serial Nos. 537,802 filed February 20, 1922 and 544,155 filed March 16, 1922.

The high audible frequency of. 6,000 is selected because it is well adapted for operating the limiting cut-off device. The output of the photo-electric cell is then preferably passed to an amplifier tuned to the frequency of light interruption (1,000 cycles). The

audio frequency current of 1,000 cycles is then used to operate a relay, recorder or telephone after rectification.

' It is seen that the recorder receives a current for the spaces between the signal elements. It may be arranged to give a normal. record, i. e. onein Which the marks cor respond to the signal elements in any suitable manner.

The operation is in, general similar to.

that already described. The 1,000 cycle'fre quency is impressed on the galvanometer when the signal is coming in as well as when there is no signal. By suitable adjustment the deflection of the galvanoi'netcr is zero The arrangement is such that under those conditions the light, interrupted 1,000 timesper second, falls on the photo-electric cell as shown in Fig. 3, where the dotted lines indicates the band in which the photo cell receives light from the galvanom'eter.- When the currentcarries the mirror so that the light is beyond or does not reach this hand, no current is delivered by the photo-electric cell. As the lightstrikes the band an output current of,

1,000 cycles is delivered to succeeding devices. Figure 3 is a curve showing the re lationship between deflection of the galvanometer as ordinates and time as abscissae, the black portions indicating the periods when the galvanometer mirror is illuminated by the lamp 27 and the unshaded portions where the illumination is cut off by the revolving screen 28. The uniform undulations at B and I) are caused by the 6,000 cycle current induced in 26 from the coil 24. In Fig. 3 the first portion of the diagram shows a space with no signal or static current present. When a dot or a dash is re ceived a rectified current of a frequency of 6,000 cycles is impressed on the galvanometer and the resulting increase in the deflection of galvanometer is such that the light no longcrstrikes the photo-electric cell, or in other Words, the band of rectification shifted so that no current is delivered by the photo-electric cell. The second portion of Fig. 3 indicates a dash with no static interference present. In the space following the dash the band shifts back to the photo cell, but an impulse of static f is present.

This impulse momentarily raises the current to the band where the signal operates, but does not keep the operation in the upper band long enough to break up the current delivered by the photo cell. The musical tone may be somewhat affected but the change will scarcely be noticed in the telephone. In the fourth portion the received current corresponding to the dash carries the band off of the photo cell aperture. lVhile the received energy is on, the static may from time to time break down the band as indicated by the static impulse f but this will only be for short periods which on the average will be different from the 1,000 cycle note and will be eliminated by the tuning to audible frequency. As the energy which gets into this audio tuning device is only that derived from the photo-electric cell there is no possibility of shock excitation, as large impulses have no way of communicating their energy directly into the tuned circuit.

Unusually strong static will, of course, affect the system as shown in Fig. 3-as f, and f but in a way which will eliminate the 1,000 cycle band with the received energy on or off. Static therefore can never give a marking period by itself, as shown by B and D on Fig. 3, since it is not of sufficient duration to effect the receiver, other than is shown by Fig. 3. I

This arrangement has a further advantage in the fact that the band frequency of 1,000 is independent of the incoming frequency ltlf) in every way, so that it, as Well as its audio tuning, may be fixed.

The transmitter or the rela s will obviousously be reversed so that the signal may be read more easily. W

F a and 5 s -ovr arrangements similar to l 2 but using a different type of limitu" The aucio frequency output of is passed through a double rectifier. agnetron of the type shown in Hull Patent No. 1.314.091 comprising a. heated filament 20 and a plate 30 surrounding the filann l the limiting cut oil. The Jl cuit is coupled to an quencv after 0 L a relay soul le rectifier are connected enclosi re and a nected to a 500 cy oscil ator to produce will give two variations of qucncy amplifier is tuned to this iroquency.

the magnetron control coil 31 this will bias prouuce a one-sided 17c intensity If the rectification is sufiiciently strong, the

\1 I amplifier tuned per-ales telephone or recort indicating the cur iron? the Wound around the outside o Cfill' the band or read field so that a 1,000 cycle var are "onward on the control and the 500 cycle oscillator will which Will depend on the relat signal.

field or and by coil 31 will prevent the of any plate-filament current. Neither the signals nor the audio tone will then beyond the magnetron. Even if the addition of rectified signals is not sufiicientto actually cut oil the curr nt in the plate circuit, the rectified curl will cause the magnetron to operate on one side 01" the characteristic curve so that the tone will be chanced upon the addition of rectified als from 1,000to 500 and this tone will be greatly reduced in the subsequent circuits tuned to a frequency of. 1,000. 0 shows characteristic curve of the magnetron, ordinates being the plate current and 1e abscissa the control voltage. iVhen the 500 cycles control is applied the control voltage varies from V to V and the plate current from T to P. It the rectified voltage V is sufiiciently strong to carry the magnetron. substantially above the cut-oil poin then ii a added 500 cycle control varies the voltage from V, to V and the plate current is cut off completely. 11'? the rectified signal voltage is V, the superimposed 500 cycle voltage causes variation of control voltage from V to V so that a 500 cycle variation of plate current results which is greatly decreased by the subsequentcircuit tuned to 1,000 cycles.

In this system as in the-photo cell arrangement described, no efii'ect is produced dire ly in the second audio tuning by the tone produced iy the signal or static as some high audible frequency is selected for modulation. For example, 3,000 cycles which after double rectification becomes 6,000. All that static may do is to raise the control current in the magnetron to such a point that, the 1,000 frequency tone produced by the local 500 cycle oscillator is reduced. ()n. account oi? the high period used, the of static will not be very prolonged so mat large part of the static W'll produce effects of such a short duration as not affect the 1,000 cycle note to any great ex- Only under very rare conditions can tent. static produce the r-ceding note 01 1,000 cycles when the signal is on, as the times when static would oppose the signals for a time interval commensurate with the audio o of 1,000 cycles would be very seldom. the arrangement of Fig. 5 a tube is if similar to the magnetron of Fig. 4. i. the external coil 31 a control e the tube is used for varying rent and as the plate current ey as that of the applied emf, a 1,000 cycle local oscillator is utilized in place of the 500 cycle oscillator. Therectii frequency of 6,000 is applied to H a l control coil 31. In this case the gnetic control would be polarized to a point a just above the lower cut off limit,

;c that the addition of any opposed rectified signals will carry it back to Z) and cut off the etl'ect ot the audio oscillator on the plate which is connected to the tuned amplitier as for the magnetron. The action of this arrangement for static and signal Would be very similar to the magnetron arrangement of nig. 4.

Having described my invention, What I claim is:

1. The method of receiving radio signals through static, which consists, in receiving radio signals and static, in normally producing observable effects from the receipt of static energy during non-signalling periods and in 'nterrupting the said observable effects upon receipt of desired incoming signal energy and static sii'nultaneously.

2. The method of receiving radio signals through static, Which consists, in receiving signals and static, in producing observable efiects from static pulses alone in the absence of received signals, in preventing the production of said observabl efiects due to said static during periods when signals of the desired character are received jointly with said static effects, and in interpreting the desired signals from the absence of said observable eiiects during periods when both static and signals are being received.

ed by means of this grid at the 3. A method of receiving radio signals through static,which consists, in normally producing observable effects from static disturbances at periods when signals areinterrupted, in interrupting production of said. observable effects during periods when signals and static are received simultaneously, and in interpreting the desired signals by the absence of said observable effects as interrupted by the simultaneous reception of signals and static. T a

4. The method of receiving radio signals through static which comprises causing received static energy to actuate an indicatorunresponsive to signal oscillations, and ren dering said indicator unaffected by said static during periods when desired signal oscillations are received.

5. The method of receiving radio signals through static, which consists, in normally receiving signals and static, in actuating an indicator by received static during nonsignalling periods, in causing desired signals received simultaneously with said static to prevent the actuation of said indicator, and in interpreting desired signals by the absence ot'any indication during periods when signals are received. i

6. The method of receiving radio signals through static which consists in producing at the receiving station a substantially continuous efiect normally observable during static periods, and in causing the desired received signals to render said efl'ect substantially unobservable.

7. The method of receiving radio signals through static, which consists, in receiving both signals and static, in producing observable effects by the receipt of said static, in producing a. different observable effect at the receiving station during periods when static disturbances are reduced in, intensity, and in rendering said eil'ects unobservable during periods when desired signals are received simultaneously with said static disturbances.

8. The method of receiving'radio signals through static which consists in si ultaneously receiving signals and static, and in causing said received signals of predetermined strength to prevent response'in an indicator normally unresponsive to signal.- ling oscillations and normally responsive to static disturbances, whereby the said static will produce an. observable effect on said indicator only during intervals when signalling oscillations are interrupted.

9. The method of receiving radio signals through static which consists in simultaneously receiving both static disturbances and transmitted signals, producing a response by said received static in an indicator unresponsive to signalling oscillations but normally responsive to said static, introducing into said indicator a substantially continuous effect observable by means of said indicater during periods when no signalling os- 'cillations or static are recelved, and in causing said received signalling oscillations to render said indicator normally unresponsive to both said static'and said continuously said indicator to respond to static disturbances received alone, and to be unresponsive to static disturbances .when received simultaneously with received signalling oscillations, v i

12. In a radio receiving system, the combination 01"" a signal receiving circuit for receiving both static disturbances and desired signalling oscillations, an indicating means for indicating both the static disturbances and the desired signalling oscillations, and a limiting cut-oil means associated'with said receiving circuit for causing a response in said indicator only at periods when the received energy falls Within predetermined limits so chosen as to normally include only the energy of the said static disturbances, whereby the said indicator is normally responsive only to static disturbances during periods when there is an absence of signalling oscillations on the receiver and the said indicator is normally unresponsive when both static and desired signalling oscillations are received simultaneously.

13. In a radio receiving system, an antenna. circuit, a resonant circuit coupled therewith for receiving signals of a desired character and static disturbances accompanying said desired signals, an'indicator associated with said resonant circuit and arranged so as to be normally unresponsive to determined band, and an indicator actuated by the output energy from said limiting cut-oil means and arranged so as to'respond only to the uni-directional pulses lying within said predetermined band.

15. In radio receiving systems, the combination of a receiving circuit for receiving desired signalling oscillations and static dis turbances accompanying the same, a rectifier for converting static disturbances when received on said receiving circuit in the ab sence of signals into uni-direction pulses of a magnitude normally lying within a predetermined band and for converting desired signalling oscillations into uni-directional pulses of a magnitude normally outside said predetermined band, an indicator, and galvanometer means actuated by said rectifier for rendering said indicator responsive only to uni-directional pulses lying within the said predetermined band, whereby the receipt of said desired signalling oscillations produce an absence of any recording effect upon said indicator and signals are determined in an inverse order.

16. In radio receiving apparatus, the com bination of a receiving circuit, a rectifier associated therewith, a limiting cut-off operated bythe output of said rectifier, an indicator controlled by said cut-oft, said cut-off being so arranged as to permit said indicator to respond only to current strengths of a value less than that of a predetermined value of currents normally produced by received signalling oscillations and to prevent response of said indicator when the current strengths are equal to or greater than the said predetermined value normally produced by received signalling oscillations.

17. In radio receiving apparatus, the combination of a receiving circuit for receiving desired signalling oscillations and such static disturbances as accompany the same, an indicator associated with said receiving circuit and arranged so as to be normally responsive only to static disturbances and so as to be unresponsive to desired signalling oscillations, means for locally supplying a disturbing effect to which said indicator is responsive, and means for interrupting the production of said disturbing effects upon said indicator when signalling oscillations are being received, said means being adapted to prevent interruptions when static only is being received.

RICHARD HOXVLAND RANGER.

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