US2082935A - Radio signaling system - Google Patents

Description

June 8, 1937. E. H. ARMSTRONG 2,082,935

RADIO SIGNALING SYSTEM Original Filed Aug. 6, 1927 5 Sheets-Sheet 1 Riff/f CUR/REA! T June 8, 1937. E..H. ARMQTRONG` 2,082,935

RADIO SIGNALING' SYSTEM original Filed Aug. 6,' 1927 s sheeis-sneei 2 June 8, 1937. E. H. ARMSTRONGA 2,082,935

RADIO SIGNALING 'SYSTEM l i original Filed Aug. e, 1927 s shets-shet 5 Patentedl June 8, 1937,

Edwin H. Armstrong, New York, N. Y.

`Application August s, '1921, serial No. 211,046 Renewed November 9, 1933 14 claims. w1. 25o-sj 'Ihis invention relates to radio signaling and has for its principal ultimate object to provide a method of and apparatus for the reduction of atmospheric disturbances 1n radio Signaling.

Another object is to provide a radio signaling system which, for a given amount of energy transmitted and a given distance of transmission, causes a much greater response in the receiver than in the case of systems now in use; and/or for a given amount of energytransmitted and a given desired magnitude of response in the receiver, greatly increases the distance of transmission over that' obtained with systems now inuse.

Further objects and advantages will appear as the invention is hereinafter disclosed and claimed.

The diculty of the problem of static inter-k ference (undesired atmospheric disturbances) is 25 terfering responses in the indicator.

The present method is based on the discoverythat the distribution of energy with respect to frequency of the natural waves is such that at any instant the energy in the component at a t given frequency is substantially equal to the energy at a closely adjacent frequency, and `that in a crash or burst of static both these frequencies will be present simultaneously. f In accordance with the now preferred method of the present invention, a special form of signaling wave is employed at the transmitter and a novel method of electrical selection at the receiver. The special form of transmitted wave 40 has a characteristic not found in the waves of natural origin.

The apparatus hereinafter disclosed employing the new method of electrical selection has the characteristic of acting cumulatively with 45 respect to the signaling waves but differentially e with respect to the waves of natural origin, so

v that the first are augmented but the latter subq stantially balanced out. e

In accordance with the form of the present 50 invention hereinafter disclosed, signaling is accomplished by transmitting alternately two frequencies, both of-wh1ch are used, one frequency as the marking wave and another close to it as the spacing wave. The difference between these 55 two frequencies is determined by considerations whin will be explained hereinafter, being made suillciently small-so that both frequencies are f received with equal facility.

Reception is accomplished by an arrangement of apparatus which is capable of separating practically instantaneously the two desired frequencies and which is so arranged that an opposite effect is produced on the indicator by one frequency when present alone as compared to the effect produced by the other frequency whenl present alone. When both frequencies are present, as in static disturbances, the effects on the indicator substantially cancel or neutralize each other. In general the result is obtained by integrating the received frequencies and causing the resultant effects to act cumulatively or differentially on the indicator as the case may be.

Referring to the drawings which illustrate and explain what I now consider preferred apparatus for carrying the invention into practice:

Fig. 1 diagrammatically illustrates the transmitting apparatus.

Fig. 2 diagrammatically illustrates the receiving apparatus. t

Fig.`V 3' illustrates the characteristic curve of the selector C, shown in Fig. 2, when straight line rectification is accomplished. e Fig. 4 Villustrates the combined characteristic curve ofthe filter equalizer B and the selector C,

shown in Fig. 2, for signal strength sumcient to give straight line rectification. e

Figs. 5 to 12, inclusive, are copies of tape records made as hereinafter explained.

Referring now to Fig. 1 which illustrates the transmitterVaregenerative oscillator i, 2, 3, is provided with smallcondenser t in its frequencycontrolling circuit arranged to be cut in by a key 5. The value of the condenser 4 is arranged in the case of a long wave transmitter, to change the frequency by an amount lying between, say, 25 to 100 cycles. In the case of a short Wave transmitter it maybe advantageous to use a frequency change which is greater than in the case of long wave transmission although the increase required is much less than that which would beproportionate to the increase in the generated frequency.l A power amplifier system 6,- 1, 8, is shown connected to the antenna system 9, I0, and to the output side of the oscillator system.

The construction and operation of the transmitting system will be appreciated by those skilled in the art, in view of the foregoing description.

ing the three-electrode vacuum tube I) generwhen the key 5' is open and oscillations" cfa difates oscillations of one predeterminedffrequency ferent predetermined frequency when the lrey'J 5 form of heterodyne receiver with the usual tuned is closed. The oscillationsso generated areamplifledby the power amplifier systemfi', 1f, 6' (ini cluding the three-electrode vacuumtube 1)., and

fed into the antenna system 9, III. v

Referringv now to Fig. 2, A represents a standard .the rectifier at I1. Locally generated oscillations under suitable #control are supplied at I5 to the input of the rectifier I6 (a three-electrode vacuum tube) to be combined with the incoming or received frequencies by the well known heterodyne method.

B represents a. form of filtering device, one section of which is adapted to pass one of the signaling frequencies and the other section of which is adapted to pass the other signaling frequency, and which is so arranged and controlled as to equalize the amplitude of the disturbance created by static on these two frequencies. The function of this equalizer and its manner of operation will be set forth hereinafter.

The equalizer system B is connected or coupled at I9 at its input side to the output side of the audio amplifier I8, and at its output side to the input side of the selector system C. The system B is shown as comprising two tubesl 25, 26, which are three-electrode vacuum tubes. The grid circuits of these tubes 25 and 26 are connected to the secondary of the transformer I9; suitabley resistances for adjusting the damping are shown in the circuits. The grid circuits of the tubes 25 and 26 are tuned by the tuning elements 2|, 23, and 22, 24 respectively. The output or plate circuits of-the tubes 25, 26 are respectively connected to corresponding ones of the primary windings of the transformers 21, 28. One terminal of one secondary winding is shown connected to one terminal of the other secondary winding.

. Each of these secondaries is shown shunted by a corresponding one of two resistances 29, 30, each provided with an adjustable tap, each tap being connected to the input ofthe selector system C. The system B is so designed and adjusted as to accomplish the following functions, among others: to pass with equal facility each of the two transmitted frequencies and to out off those on either side (i. e. above the higher frequency and below the lower frequency) and also substantially to equalize with respect to each other the amplitudes of the static disturbances occurring above and below a certain frequency (F3, hereinafter referred to) which lies midway between the two transmitted frequencies. To effect these functions, the output transformers 21, l28 are so connected that, were the circuits 2|, 23, and 22, 24, tuned to the same frequency, and the relative amplitudes properly adjusted by means of the potentiometers 29, 30, the outputs of these transformersy21 and 29 would neutralize each other. The circuits 2I, 23, and 22, 24 are tuned respectively to the two signaling frequencies produced in the output circuit of the rectifier I6.

The selector system C has -the important property or ability of distinguishing and distinguishfaosaoss shown-Q .,Anticipating.somewhat j the mdr-eg.completev explanation of operation vherei inafter ysetf'forth, for facilitating the disclosure:

two differentsignaling frequencies are alternately impressed upon the input of the selector system f C. Thel'coinbination of the inductance 34 and condenser l33 is so designed and/or adjusted as..

to `givesubstantially zero potential across the upper terminal of the condenser 33 and the lower -terminal of the inductance 34. -In other words,

' of the inductance 34, is non-'reactive for the other of the two signaling frequencies supplied to the selector system C. An amplifier 40 which is preferably a three-electrode vacuum tube amplifier, has its grid or input circuit connected (through a transformer 38) across the combination: inductance 34--condenser 33. A similar amplifier 4I has its grid or input circuit connected (through a transformer 39) across the combination: inductance 34-condenser 33-condenser 32. It will be noted that the primaries of the input transformers of the amplifiers 40, 4I have a common connection to the lower end of the inductance 34 through a resistance 31. A resistance 35 is connected at one terminal to the lower end of the inductance 34 and at its other end to one of the leads from the output of the equalizer B and also to the grid of a three electrode vacuum tube amplifier 36; the filament of the latter being connected to the terminal of the resistance 35 that connects to the coil 34. The plate circuit of the tube 36 includes the resistance 31 and is connected to the common lead of the transformer 38, 39, as shown. The function of the tube 36 and connections is that of a resistance compensator, i. e. to cause the system to act 'as though the inductance 34, and condensers 33, 32, had no resistance.

Each of the amplifiers 40, 4I, has its output circuit connected or coupled through a corresponding one of two transformers 42, 43, to the input side of a corresponding one of two rectiers 46, 41. These are preferably two-electrode vacuum tubes or so-called Fleming valves. Each of the rectifers includes a comparatively large resistance 44, 45 connected as shown, for the purpose ofv producing substantially straight-line rectification of the currents being dealt with. Such straight line rectification is disclosed and explained in my co-pending application, Serial No. 538,856, led February 24,1922, now Patent No. 1,716,573, patented June ll, 1929. The output of the rectifiers 46, 41, connected as shown, goes to a filter system D hereinafter described.

Again anticipating the description of operation set forth hereinafter, the operation of the selector system Cinay conveniently now be explained in part.

The characteristic curve of the response of the selector system`C as measured by the combined output of the rectifiers 46, 41 for varying frequency supplied to the input side, is shown in Fig. 3. The approach of this curve to the ideal condition results from the provision of the resistance compensator 35--36--31 previously de scribed. 'Ihe resistance 35 is a comparatively small resistance, preferablyless than the resistance to be compensated for, and the resistance 31 is a largevresistance. By proper adjustment of these resistances with respect to each other,

tion and to increase with frequencyuntil a certain frequency F2 is reached, beyond which the current again does not vary materially for further increase of frequency.

I wish to emphasize an important property of the selector system C; i. e., that it distinguishespractically instantaneously between frequencies supplied to it as compared tothe time required for the usual circuit, tuned to resonance for a predetermined frequency, to distinguish between that frequency and other frequencies.

The combined characteristic curve of the equalizer B and the selector system C is shown in Fig. 4 where it will be noted that the frequencies above F2 and below F1 are substantially cut off. It will be noted further, as set forth inconnection'with Fig. 3, that frequencies between F1 and Fa (impressed upon the input to equalizer B and supplied from it to the input of the selector system C) produce aA rectified current which flows in one direction in the output of the selector system C, and that frequencies which lie between'Fa and F2 produce a rectified current that flows in the opposite direction. The importance of this characteristic or property will be more fully appreciated upon review of the complete description of the operation.

The filter system D (see Fig. 2), which receives the output of the selector system C, is shown as comprising an inductance 48, resistances 49, 5I, and condensers 50, 52, connected as shown. The design and connections are such that this filter system D will pass continuous current or currents of comparatively low frequency but substantially cut off currents of comparatively high frequencies. As will hereinafter more clearly appear, the adjustment of this filter depends upon thespeed of signaling and the relative strength of the atmospheric disturbances to the signal strength. The inductance or choke coil 48 serves also to prevent the passage to the amplifier 53 of alternating vcurrents which would paralyze or tend to paralyze it in the absence of such pre- Ventive means.

The output of the filter system D is shown connected to a D. C.ampliiier 53 of usual construction, whose output connects through a poten-v tiometer-controlled source 51, of direct current (connected as shown), through a switch to a Siphon recorder 54 (of the type now commonly employed in practice in the art to which the present invention relates) or to the usual head phones 55 having a chopper' 56 in its circuit.

The system is preferably designed, constructed, and adjusted, to operate substantially as follows.

Assume that the transmitter (Fig.'1) is so ad' justed -as to send at a frequency of l20,00() cycles per second when the key 5 is down, and at a frequency of 20,050 cycles when the key 5v is up,

and thatthe key 5 is, employed to transmit signals by theusual code of properly spaced dots and dashes and combinations thereof. To receive the signals so transmitted the receiving system (Fig.,2) may be adjusted as follows. The input circuits II, I2, I3, etc., of the system A are tuned to pass the transmitted frequencies of 20,000 and 20,050 cycles and the local source of oscillations supplied at I5 so adjusted to produce, in the output of the system A, a beat frequency of 1550 cycles whenV the frequency of 20,050 cycles is being received, and a -beat frequency of 1500 I cycles when the frequency of 20,000 cycles is being received. These two beat frequencies which occur alternately are supplied to the .equalizer system B. The circuit 2|, 23 of the system B is tuned to one of these beat frequencies and the circuit 22, 24 is tuned to the other beat frequency. The circuits of the selector system C are so ad justed that the frequency Fi (see Figs. 3 and 4) is 1500 cycles per second and the frequency F2 is 1550 cycles per second., When the key 5 (Fig. 1) is down (i. e., on front stroke to make a dot or dash depending on the comparative length of time it is held down), a frequency of 20,000 cycles is transmitted. By beating down in the receiver, this frequency of 20,000 cycles is converted into the frequency of 1500,.pycles"`(F1) which produces, in fthe'output of the selector system C, a

This rectified cur'- tion or the other depending upon the polarity of the rectified current. It will be understood that the defiection of the stylus by the current de 'scribed will persist for a length of time the transmitting key 5 (Fig. 1) is held down.

Whenv the transmitting key 5 (Fig. 1) is released; i. e., open, (i. e., on spacing or -back stroke), the operation is similar to -that set forth above, in connection with the key 5 closed, except as now noted. In this case the beat current of 1550 cycles (F2) is produced in the receiver. This produces a rectified current corresponding in amplitude and direction to that indicated for F2 in Figs. 3 and 4. It will be noted that this rectified current is of substantially the same amplitude as that produced by reception of the frequency of 20,000 cycles transmitted when the key 5 is depressed, but it is of opposite polarity. This rectified current (key 5 up or open) causes the stylus of the Siphon recorder 54 to return .to and pass through its neutral position and to be deflected in the direction 'opposite to that in which it is deflected when the key 5 is closed or depressed.-

It is important to note that the deflection of the recording stylus obtained by virtue of the system herein disclosed is double that obtained from the standard systems now in use. This doubling of deflection corresponds to what would be obtained by quadrupling the energy transmitted by a standard system, other conditions being the same i'n the two cases. Therefore, wholly aside from the reductionof static or atmospheric interference, I have provided a radio signaling system of much greater economic efficiency than the radio telegraph systems now in commercial use. In addition, as stated, I have provided a novel system of radio communication in which the disturbing effect of static or atmospherics is greatly reduced. This aspect of the operation of the sys- ,tem will no'w be dealt with by considering what happens in the receiving system when a band of frequencies, such as is contained in a group of atmospheric discharges, is received.

Over a comparatively short interval of time there will be substantially the same amount of energy impressed by the static or atmospherics upon the input of the selector system C between the frequencies F1 and Fa as between the frequencies Frand F2, Over short intervals of time, due in part to inequalities of heterodyning because of the particular phase of the heterodyning current with respect to the phase of the incoming disturbances, more energy may be in the lower or higher of the two frequency bands. The equalizer B reducesthis inequality so that there are delivered to the selector system C two bands of frequencies of practically the same energy. These two bands are separated in the selector system C into high and low frequency groups, which are supplied respectively to the rectifiers 46, 41, converted thereby into rectified form, and the two rectified outputs differentially combined to oppose and substantially neutralize each other.

y#While over a period of time the balance is practically perfect, over short intervals of time it happens that the lower of the two frequency bands produces a greater amount of energy and a larger value of rectified current than the higher frequency band, and vice versa. Thisl results in the presence in the output of the selector system of a residual disturbance which is an a1- ternating current of irregular frequency which more or less rapidly reverses. Since the current produced in the receiving system, and present in the output of the selector system C, by the energy transmitted at the transmitting station duiing the `intervals of a dot, a dash, or a space,

is substantially a continuous current (or at very high speeds of sending, a lower frequency current than the residual disturbances), the filter system may be and preferably is provided and adjusted so as to block the passage of the residual disturbances to the signal-indicating device 54 or 55.

To the best of my present ability and knowledge I have set forth the theories and explanations upon which I now believe the operation of my features of invention depends, and whereby they may be practiced by those skilled in the art having the foregoing disclosures before them. These theories and explanations appear`to be borne out by extended tests and demonstrations that I have made. However, it may later appear in the light of further development that the theories and/or explanations advanced are not wholly accurate, and I shall therefore in addition disclose in considerable detail a physical embodiment of the invention and results I have obtained with it.

The transmitting apparatus was adjusted to generate and emit oscillations at a frequency of 20,060 cycles per second withthe key (Fig. 1) raised or open and at a frequency of 20,000 cycles per second with the key 5 down or closed. No further comment need be made with respect to the adjustment of the transmitter.

The receiving system embodied as its collector of energy on outdoor antenna and the static impressed upon it was natural as distinguished from artificially created static. The signais were impressed upon the receiving antenna from the oscillation-generator whose oscillations, as stated, were "transmitted at a frequency of 20,060 cycles per second with the key 5 up and at a. frequency of 20,000 cycles per second when the key 5 was down. I shall now proceed lto give such information and constants of the receiving apparatus employed by me (see Fig. 2) as will enable those skilled in the art to reproduce it and the results obtained with it.

The apparatus A. was standard apparatus and needs no further comment. The transformer I9 .was a step-down transformer having a ratio of transformation of 10 to 1; the' resistance 20 was variable from a few ohms to 100 ohms and adjusted according to the speed of signaling; the inductance 2| was 0.34 henry; the inductance 22 was 0.31 henry; the condenser 23 had a capacity of 0.05 microfarad; the condenser 24 had a capacity of 0.05 microfarad; the transformers 21, 28 were step-down transformers each having a ratio of transformation of 4 to 1; the resistances 29, 30 each had a maximum resistance of 400 ohms; the condenser 32 had a capacity of 0.5 microfarad; the condenser 33 had a capacity lof 0.05 microfarad; the inductance 34 was 0.34

henry; the resistance 35 was variable between a few ohms and 100 ohms; the resistance 31 was 4000 ohms; 38, 39 were ordinary audio frequency intertube transformers; 40, 4I were standard three-electrode vacuum tube amplifiers; 42 and 43 were ordinary output transformers each having a ratio of one to one; 44 and 45 each had a resistance of 6000 ohms; 48 was a choke coil of about 25 henrys; 49 and 5| were each variable between 25,000 ohms and 50,000 ohms in steps; 50 and 52 were each variable Ybetween zero and 0.1 microfarad in steps; and 53, 54, etc. were standard apparatus previously described needing no further comment. The circuits I2, I3, I4 were tuned to admit either of the transmitted frequencies, i. e. 20,000 and 20,060 cycles per second; the local generator of oscillations was adjusted to supply, at l5, oscillations at a frequency of-21,280 cycles per second, producing with the received frequency of 20,060 a beat frequency of 1220 cycles per second and producing with the received frequency of 20,000 a beat frequency of 1280 cycles per second. 'Ihe circuit 2I-23 was tuned to one of the signal beat frequencies--1220 cycles per second, and the circuit 22-24 was tuned to the other signal beat frequency-1280 cycles per second, the F3 frequency being about 1250 v cycles per second.

In Figs. 5, 6 and 7, I have shown copies of some tape records made with my apparatus above described when no static or interfering energy was impressed upon the antenna of the receiver. The tape record reproduced as Fig. 5 was made by first establishing the base line in the middle of thetape with the transmitter dead (i. e., with the plate circuit of the oscillator tube of the transmitter open), then closing the key 5 and keeping it closed while interrupting the plate current (in the usual manner by a. key not shown) of the oscillator tube of the transmitter to cause the dot and dash signals to be transmitted. The tape record reproduced as Fig. *6 was similarly obtained but with the key 5 open so that the condenser 4 was not in circuit. It will be noted that in one case the stylus Wasdeiiected in one direction from the base line (middle) on the marking strokes and returned to the base line (middle) on the spacing strokes, while in the other case the stylus was deflected in the opposite direction from the base line (middle) on the marking strokes,

l returning to the base line (middle) on the spacing strokes. The tape record reproduced as Fig. '7 was made by first establishing the middle line with the transmitter dead, as in the case of Figs. and 6. 'Ihe plate circuit of the oscillator tube of the transmitter was then permanently closed, and the key 5 employed to cause the dot and dash signals to be transmitted.

Comparison of the actual record shown in Fig. '7 with those shown in Figs. 5 and 6 confirms the statements that I have previously made, i. e. that the deflection of the recording stylus (-Fig. '7) obtainable by virtue of my invention is double that obtainable from standard methods of signaling,

and that, therefore, wholly aside from` the reduction of static or atmospheric' interference, I have provided a radio signaling system of greatly improved economic eiciency.

In Figs. 8, 9 and 10 are reproduced actual tape records showing the effect of natural static impressed'upon, i. e. received by, the receiving antenna, no signal being received. The base lines of these records are at the middle of the tape in each instance. Thecurve reproduced in Fig. 8 was made by removing one of the tubes '46, 41 from the system, i. e.'working only one side of the balance, and the curve reproduced in Fig. 9 was made by replacing the tube previously removed and removing the other of the tubes 46, 41,

i. e. working only the other side of the balance.l

'with respect to the energy of the static frequencies below the mid-frequency F3 (Fig. 10). will be noted also that in Fig. 8, as in the case of standard systems, the static-.produced impulses are above the base line and produce a varying unidirectional current which cannot be successfully filtered out if present alone. However, in my system there is simultaneously produced (Fig.

9), by the static, varying unidirectional current of opposite polarity, which when differentially combined with the first mentioned unidirectional current leaves only a residual (Fig. 10) having no substantial direct current component but which is a current which fairly rapidly reverses in polarity and may be successfully filtered out.

The tape record reproduced in Fig. 11 was made with standard receiving apparatus, while that reproduced in'Flg. l2 was made with my apparatus embodying my invention.

In both cases; the same code signals were transmitted and received and at 'the same speed. The two records were made closely in succession in point of time with the same outdoor receiving antenna subjected to substantially the same natural static in both cases. The effect of the static upon the indications with the standardreceiver are clearly apparent in Fig.-11. In the case of my apparatus embodying my invention the. static disturbances, which in the case of the standard method of reception were sufficient to prevent operation, were practicallyeliminated and do not appear in the record of the indications (Fig. 12). It will be apparent that the signals recorded on the tape reproduced in Fig. 12 could have been transmitted and recorded at lvery much greater speed before reaching a condition in which their readability would be impaired.

It will now be apparent that, in addition to increasing the economic efficiency of radio signaling by virtue of the double deflection obtainable and spoken ,of hereinbefore. my invention effects great improvement inthe economic efli ciency by virtue of the reduction of the disturbing effects of static or atmospherics. For the same degree of readability the speed of transmission and reception may be greatly increased as compared to that obtainable with the standard methods of signaling. Furthermore, it renders possible facsimile transmission under static conditions and at such speeds impossible with the standard systems now in use.

In view of the foregoing disclosure, it will be understood of course, that the frequencies supplied to the more important parts of my system, for example, to the input of the equalizer B, need not be audible frequencies but may be radio or intermediate frequencies. In other words, the

frequencies F1, F2 and Fa (Figs. 3 and 4) mayA have other numerical values than those hereinbefore specifically mentioned or referred to', by suitably selecting the constants in accordance with the principles disclosed.

It will be further understood that certain features of my invention above disclosed may, within the scope of appended claims, be modified and/or omitted depending upon the extent to which the improved results are desired, and that certain instrumentalities and/or groups of instrumentalities may be employed in radio signaling systems in which other results are attained. Thus it\will be apparent that some of the features of invention herein disclosed are claimed in my Patent No. 1,941,447, granted December 26, 1934. r'

What I claim isz- 1. The method of reducing the effects in radio signaling of atmospheric disturbances consisting of simultaneously occurring frequencies, which method comprises alternately changing the signaling frequency at the transmitting station,

impressing the signal -oscillations of different frequencies successively upon the receiving system, causing the successively applied different signal frequencies tol act cumulatively in producing indications, causing the received atmospheric frequencies to act differentially with respect to signal frequencies to act cumulatively, causing the undesired frequencies to act differentially with respect to each other, and adjusting the differential action under varying conditions to cause the effect produced by a portion of the undesired frequencies Ato be substantially equal to the opposite effect produced by the remainder of the undesiredfrequencies.

3. A method of increasing the extent of the signal-recording stroke of the signal-recording stylus in the receiver of a `radio telegraph system in responsey to transmitted radio telegraph signals, which method comprises transmitting oscillations of \one frequency during spacing intervals, transmitting oscillations of a different frequency during other signaling intervals, lmpressing said oscillations upon a receiving system, causing the oscillations of the first mentioned frequency to produce a deflection of a recording stylus in one direction from neutral position, and causing the oscillations of the second mentioned frequency to produce a deection of the recording stylus in the opposite direction from neutral position.

4. The method of reducing the eect in radio signaling of atmospheric disturbances consisting of simultaneously occurring frequencies, which method vcomprises causing received frequencies above a predetermined frequency to produce a rectified current in one direction, causing received frequencies below said predetermined frequency to produce a rectified current in the opposite direction, differentially combining said rectifled currents, and filtering out undesired residual currents.

5. The method of reducing the effects in radio reception of atmospheric disturbances consisting of simultaneously occurring frequencies, which method comprises substantially equalizing the energy produced by received static frequency components above a predetermined frequency with respect to that produced by received static frequency components below s aid predetermined frequency, causing the first mentioned energy to produce a rectified current in one direction and causing the second mentioned energy to produce a rectified current in the opposite direction, differentially combining said rectified currents, and filtering out undesired residual currents.

6. Apparatus for increasing the extent of the signal-recording stroke of the signal-recording stylus in the receiver of a radio telegraph system in response to transmitted radio telegraph signals, the said apparatus comprising in combination, transmitting means including a key, means for transmitting oscillations at a predetermined frequency upon closure of said key, and means for transmitting oscillations at a different predetermined frequency upon release of said key; and receiving means comprising a recording device and frequency responsive means for causing movement of the stylus of said recorder in one direction upon reception of oscillations at one of said predetermined frequencies and for causing movement of the stylus of said recorder in the opposite direction upon reception of oscillations at the other of said predetermined frequencies.

7. In a system of the class described, energyequalizing means comprising in combination, a

first tuned circuit, a second tuned circuit, means for supplying energy jointly to said circuits, a three-electrode vacuum tube having a grid circuit connected to said first mentioned circuit, a three-electrode vacuum tube having its grid circuit connected to said second mentioned circuit, a pair of transformers each of which has its primary winding connected to the plate circuit of a corresponding one of said vacuum tubes and one terminal of one secondary winding connected to one terminal of the other secondary winding, a resistance connected across one of said secondary windings, a resistance connected across the other of said secondary windings, and a circuit connected across said resistances. l

8. The method of reducing the effects in radio signaling of atmospheric disturbances consisting of simultaneously occurring frequencies, whichv methodcomprises alternately changing the signaling frequency at the transmitting station, impressing the signal oscillations of different frequencies successively upon the receiving system, causing the successively applied different signal frequencies to act cumulatively in producing indications, causing a portion of the received atmospheric disturbances to produce a current of one polarity, causing another portion of the received atmospheric disturbances to produce a current of opposite polarity, and combining said two currents of opposite polarity. v

9. 'Ihe method of reducing the effects in radio signaling of atmospheric disturbances consisting of simultaneously occurring frequencies, which method comprises alternately changing the signaling frequency at the transmitting station, impressing the signal oscillations of different frequencies successively upon the receiving system, causing the successively applied different signal frequencies to act cumulatively in producing indications, causing a portion of the received at currents.

10. A radio signaling system comprising in combination, an indication-controlling circuit, means for producing in said circuit a signal-controlling current which reverses in direction comparatively slowly, means fo'r causing a portion of undesired received energy to produce a substantially unidirectional varying current in said circuit, means for causing another portion of the undesired received energy to produce in said circuit a substantially unidirectional varying cur.- rent of opposite polarity to said second mentioned current, and means connected to said circuit for impeding the passage of the combined current produced by the undesired energy but permitting the passage of the signal-controlling current.

11. In a radio receiving system, in combination, a group of reactance elements which are nonreactive at a certain frequency, another group of reactance elements which are non-reactive at a different frequency, means controlled by received oscillations for causing currents to fiow through said groups of reactance elements, a circuit connected across the first mentioned groupof reactance elements, a rectifier controlled by said circuit, a circuit connected across the second mentioned group of reactance elements, a rectifier controlled by said last mentioned circuits,

.means for differentially combining the outputs of said rectifiers, indicating means controlled by said rectifiers, and means for substantially eliminating the effect of the resistance of each of said groups of reactance elements".

12. The method of reducing fading whenY 0 and spacing energies alternately, and a receiving system comprising means to collect the radiated energies, means to separate the marking and spacing energies, means to separately rectify the marking and spacing energies, and a translating 5 device responsive to one of the rectied energies in one sense, and to the other of the rect-ined energies in the opposite sense, so that both or either of the marking and spacing energies will produce a readable signal..

:0` 14. An arrangement for reducing fading when transmitting code signals on short waves includlng a transmission system comprising a short wave transmitter, keying means for slightly changing the frequency of transmission to distinguish between marking and spacing periods,

` and means to radiate the marking and spacing energies alternately, and a receiving system comprising means to collect .the radiated energies, means to heterodyne the collected energies to energies of intermediate frequency, means to separate the marking and spacing intermediate frequency energies, means to separately rectify the marking and spacing energies, means to reverse the phase of one of the rectied energies, means to combine theresulting energies, and means to translate the combined energy, so that both or either of the marking and spacing energies will produce a readable signal.'

H. ARMSTRONG.

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