US2200789A - Apparatus and method of eliminating signal fading - Google Patents

Description

L. D. ECKARD 2.200.789

APPARATUS AND METHOD OF ELIMINATING SIGNAL FADING May 14, 1940.

Filed Oct. 6, 1938 2 Sheets-Sheet l y 14, 1940- L. D. ECKARD 2.200.789

APPARATUS AND METHOD OF ELIMINATING SIGNAL FADING Filed Oct. 6, 1958 2 Sheets-Sheet 2 [5 chance in wo -c5 METIHQD til? ELIMINA'IING SHENAL FADENG;

' Lewis I). ammo. won

. lppiic'ctlon October d, 19913, T; N tfiilttfii 2t @iolme. ltli.

lite present invention roletcs to means for the chance the capocity of the conor condensers in wave receiving means variations of atmospheric pressure is. a phenomenon which has always been troublesome in signal receiving sets.

The earth's surface is belted with a. continuouely moving bond of air. The current 01' all flows from west to east. The band of continuously moving all varies in height throughout its poth and at any given point on the earth's enclose the atmospheric pressure varies due to the increasing and decreasing height oi the column or air thereover. It is the w continuous movement of this layer of air with its varlence in height that causes variations in barometric pressure. The higher the column of .air over any given point on the earth's surface the greater the barometerlo pressure and correopondingly, the lower the column of air, the lower the barometric pressure. This movement of the air current over the earth's surface causing voilctions in barometric pressure at a given point is lmown. us the p variations in atmosphccic pressure.

Beyond the moving layer oi air which overthe eovth and which gives rise to the primary vovlotions in atmospheric pressure. is a. secondleyer. In this secondary layer there are minute variations of the air preseure which occur oil the timevin more or less uniformity.

These variations are called the secondary variation; of ctmoepheiic pressure and possess a pul outing movement.

It was found by enpcaiment that radio siznala, particularly those signals received as airy waves. faded most when the barometric readings varied extensively and that it was necessary to adjust the capacity oi, the timing condensers o! the m radio receiver before the signal could be brought hook to its original volume. At the barometric oeure increased the frequency of the signal increased and it won necessary to decrease the capacity oi the tuning condensero to azain obresonance. Also, as the atmospheric preeeiu'c decreased it was necessary to increase the opacity of the taming condensers in the radio circuit to regain reeononm. Tins proves that the iteouency of wave or signal varies according to in atmospheric precwre and it in whetl'ier the sending station is crystal co trolled or not.

exicoente show the 'ilorometrlc change in "oliovrlne oi ire Kilo-cycle: Milli." (uppm!1mate1y) 0.05 0.01" .;do 0.5 id" do 5.6

From. the ebovc table it can readily be seen 6 that variations in atmospheric pressure cause a frequency driit.

Now it is believed that this frequency drift is for the most part caused by the secondary variatione, which a pulsating wave movement. This pulsating movement causee a change in the magnet flux density of the ionized layer which contains ozone, a magnetic gas. Durimz, a contractlng or crowding period of the molecules and ions in the secondary layer, the magnetic field is shortened resulting in an increased number per unit area of electrostatic and magnetic fields thereby increasing the frequency of the radio wove travelling therethmugh. During periods of depression or rarencation the magnetic fields are lengthened and the electrostatic fields are further apart resulting in a lower frequency 01 the wave passing therethrouzh.

This pulsating or secondary wave movement could be caused by the concerted pulsation of u the molecules of the atmosphere due to the absorption oi energy irom the cosmic rays. It is known that molecules are composed of positive protons in a nucleus and have nezative electron revolving about the protons in various enercy levels. The electrons of any one molecule absorb energy from the cosmic rays and the protons of that molecule radiate the absorbed en erg'y. It creates a pulaation in the molecules similar to the movement of the lungs in breath- 35 ing. Our lungs expand when we absorb or take in air and contract when we radiate or exhale the used air.

It is to be understood that the theory is advanced only as on aid in understanding the in w vention and that a paper is to be published at a later date giving a detailed explanation of secondcry variations in atmospheric pressure.

It is broadly the concept of this invention to w provide a variable reactance device responsive to minute variations in atmospheric pressure end which automatically cooperates with the tuning circuit of a wave receiving set to aubstuntially eliminate signal iadinc due to the minute varia m tions in atmospheric pre'smre; and wherein the -receiving set is kept in complete resonance.

(lomplete resonance depends upon a proper reintion between the capacity, inductanceand reaistamoe in the tuning circuit. A frequent shift I! in the carrier wave, unless compensated for, would destroy complete resonance in the tuning circuit and give the effect of fading in the wave receiving set. To compensate for the frequency shift of the carrier wave due to minute variations in atmospheric pressure, the variable resctance device which is responsive to the minute atmospheric variations, is placed in the tuning circuit of the wave receiving set, so that any minute variation in atmospheric pressure causes a variation in the reactsnce device to maintain the tuning circuit resonant to the frequency of the carrier wave. 1

The present invention has for-its primary ob ject the provision of a variable condenser which -is sensitive to primary and secondary variations in atmospheric pressure and which cooperates with a wave receiving device to automatically eliminate fading.

The present invention is adapted to be used in combination with any wave receiving means, such as radio telephone, telegraph, television, so lective ringing, radio telephone circuits, dircc tionsl finders, beams, depth indicators or in any other system or circuit which depends on radio waves being propagated through the atmosphere or water and which is tuned to resonance by vary ing capacity, inductance or resistance.

An object of the invention is to eliminate alg nsl fading in all wave recelvins devices and more particularly in radio receiving sets.

Another object is to provide condenser means having a variable capacity controlled by atmob pheric pressure and cooperating with tuning condensers to eliminate signal fading in receiving lets.

Another object is to provide an automatic barometrically controlled variable condenser cooperating with the tuning condensers of signal receiving means to eliminate tonal volume changes.

Another object is to provide variable condenser means, the capacity of which is automatically responsive to barometric pressure changes and which cooperates with tuning condensers in wave receiving means to eliminate fading. Another object is to provide a. small inexpensive auxiliary condenser having a thin metal lic disk adapted to pulsate with slight variations in barometric pressure to vary the capacity thereof and which may be inserted in the tuning circuit of a wave receiving device either in parsllel or in series with the tuning condensers thereof to automatically alter the capacity of the tuning condensers and to thus eliminate fading.

Another object is to provide means responsivc to atmospheric pressure changes and asso eluted with a wave receiving device to substantlally compensate for the frequency drift of the carrier wave due to atmospheric pressure changes whereby the frequency of the carrier wave is maintained in resonance with the wave receiving device.

Another object is to eliminate extraneous noises in the wave receiving set such as the sound comparable to the noise of the ocean waves.

Another object is to provide a variable condenser in which mercury, which is responsive to minute and major atmospheric We changes,

serves as one of the electrodes of the said condenser.

Another object is to provide an auxiliary variable condenser sensitive to secondary and pri mary variations in atmospheric pressure which electrically cooperates with the tuning condensers of a radio set so that broadcasting stations always come in at their proper location on the dial.

Other and further objects and advantages will be apparent from the following specification and the claims appended thereto.

In the drawings where like numerals refer to like or corresponding parts throughout the seversl views,

Figure 1 is a diagrammatic view perspectively showing a vacuum cell condenser in the electrical tuning circuit oi a radio receiver and embodying the principal features of the invention.

Figure 2 is a plan view of the plates to be used as a condenser in conjunction with its vacuum cell, all shown in Fig. 1.

Figure 3 is a plan view of a vacuum cell vari able condenser and showing three conducting plates insulated from each other.

Figure 4 is a front elevation of the vacuum cell condenser showing the corrugated surface thereof.

Figure 5 is a top plan view with parts broken away of a modified vacuum cell variable con denser in the radio circuit.

Figure 6 is a side elevation with parts broken away oi the modified vacuum cell condenser showing the corrugated outer and inner surface of the cell.

Figure '7 is a side elevation oi the modified vac uum cell condenser, and

Figure 8 is a. front elevation of a mercurial barometer condenser to be used as a variable condenser in the radio circuit.

Referring now to the drawings and more par tlculsrly to Figure 1, the numeral 20 generally indicates a vacuum cell provided with a corru gated surface having a plurality of integrally connected corrugated sections 2| which are adapted to pulsate freely with minute variations in atmospheric pressure. One of the pulsatable section's is grounded, as at 22, in any conventional manner. Spaced from said grounded plan: are a plurality of insulated conducting plates, It, 24, and 2!, each of which is provided with a pro iecting lug 23a, 24a, and "a, respectively. The said plates are preferably made oi metal but may be composed of any conducting substance. The said plates are further insulated irom such other and from the said grounded corrugated sections plate automatically variable condenser, the ca pacity of which is cutomsticslly changed with the pulsations of the grounded corrugated plate which is sensitive to minute variations in 3W? v at condenser. the vacuum cell being the type 1 type at barometer it generally known in totaled to cover such combinations. The size and number of the conducting plates and vacuum cell may be changed to meet diflerent capacity requirements.

referring to Figure 1, 23b indicates a radio frequency tube, 230 an inductance coil, 23d a variable tuning condenser and Me a smaller variable condenser known as a trimmer, all of which are in an electrical tuning circuit with the plate 23. Likewise, the detector tube 241:, the inductance coil Me, the variable tuning condenser 24d and the trimmer 24c are'in the electrical tuning circult with the plate 2.

And the oscillating tube the inductance coil He, the variable tuniny condenser, 25d and the trimmer 25c are in the electrical tuning circult with plate 2!.

Figure l, as described, is a standard superheterodyne radio tuning circuit havinz one radio frequency amplifier tube Nb, one first detector or mirror tube 2%, and the local oscillator tube 2%. The tubes 23b, 24b, and 25b are each in circuit with the plates 23, I4 and 25 of the auxiliary coudenaer respectively. The pressure senritive grounded vacuum cell 2-0 when it pulsatea with minute atmospheric variations causes an automatic and simultaneous capacity change in the rat-lilo frequency, detector and oscillator tuncircuito.

. Reten lncwtofigurwt andithevacmnn cell 2 la shown suspended in a houainz comprisinn a? bone plate 3!. upright members 21 and II. A dick M which carries the conducting plates 23,

ti and a it maxed to the vertical members 21 sndfliat the upper ends thereot by means at acrewslta. The conducting plates 23. 24 and 2| which are disposed on the \mderslds oi the disk i! are insulated tron: each other and mm the conducting vacuum cell a; The met at the? vacuum mil 2% closer to or further plates-l3 3t and 2K in or ccipaclityci the condenser by width of the dielech'ic. The vacuum cell 2! is aecured at the lower end thereof to the screw, member to w h ouahtbeplateto. e show what is adapted to beturned onetime vacu'coll It be moved into a poeltionwith respect to the conducting" 1p platea28.fland2l,i.e.theairgapbetweenths cell and-the plates can be selectively increased or M M1 to decrease or increase thocapacity o! the condenser. once it is properly set it seldczn requires adjustment.

a -Re1errinx now to Figures a, Band 1 o! the drawings, a iurther modification otthe type oi vacuum cell which can be used as 7 maticaliy variable condenser is shown.

numeral ll indicates aeneraily a vacuum in an aneroid barometer vacuum cell t tar m and in Charles J.'1esliabue mg. lilo-1a {illustrated Catalogue at page 263 a hill description-la given 0! the atnicture thereof. For the pnrpmc of this invention M indicates a vacwuum ocllcmnposed of two dlskaof corrugated German silver or the like which have been solelated together and from which the air has been in cxhauctednsprinzflubeepsthevacmimcell t! colla."1he vucinim cell has the lower surface thereof secured to the plate 0. The plate M is spaced from plate 48 in any suitable manner and carries on its underside a plurality o! conductlna plateapreterably corrueither increase or decrease the width of the air phere. It is to be understood that the mercury The tile

gated, insulated from one another. The plates 48 and H are preferably composed of insulating material. The conducting plates or the vacuum cell condenser, generally indicated at ll, one or which is indicated at in Figure 5, each has a 5 lug such as "a projecting therefrom which is adapted to connect each of the conductin: plates of the vacuum cell condenser into the tuning circuit oi! a signal receiving device in a manner similar to that shown in Figure 1.

In operation, the conducting plates of the condenser are connected into the tuning circuit of a wave receiving set in a manner similar to that shown in Figure l. The vacuum cell is suitably grounded. The complete device is now an autoll matlcally variable condenser sensitive to minute variations in atmosphere pressure. Minute variations in atmospheric pressure cause the corruated upper surface of the cell 42 to move and gap between the said surface 0! the vacuum cell and the corrugated under suriace of the con-- ducting plates, thus either decreasing or increasing the capacity'ot the condenser automatically.

The air gap as shown in Figure 6 is exaggerated but must be or suiiicient width to allow for maior and minor atmospheric pressure changes, and the movement of the suri'ace oi the vacuum cell is generally only in the neighborhood of 0.001 to 0.1 inch of mercury. that is, the variations in barometric pressure due to the secondary variations of the atmosphere. The more sensitive the cell used the more exactly the capacity change follows the minute variations in atmospheric pressure.

Referring now to Figure 8, there. is shown a glass tube 80 containing mercury'llc, and having a closed end M, an open end II and an elbow portion 53. The mercury "a in the tube is balanced by atmospheric pressure and as it is undamped it is very aensitive to slight or minutes variations' in the said pressure. a plurality of conducting plates 54, I8 and BI are copper plated to the tube 5! at a point adjacent the open end 52 thereof. The conducting plates have lugs to. "a and a respectively projecting therefrom which are adapted to be connected into the electrical tuning circuit oi a wave receiving act inamannerasahowninlligure 1. Thoplatea ll, ll and B are insulated irom each other. The mercury "a is disposed in tube" or glaas or the like. so that the suriace thereof near the I opening 82, is substantially midway the height -otthe .condmtlnz plates 8. II and I8, to allow {or the severe primary movements of the atmoscurtacsneartheopening l2 mustlieinthesame horizontal plane as the conducting plates it, it and u, otherwise minute atmospheric presume chance would produce no capacity change in the tuning circuits of the wave receiving device. The

"-xnercury lla can be :rmmded directly by placing a wire directly in. contact with the mercury through theopeuinzll. or a capacity ground can beuaedbysecurinzametalband ilbtothc' tube 5. at a point preferably above the elbow I! on the longer arm otthe tube II and groundingthe metalbandasatilc. Itis preterredto directly ground the mercury.

Themercury condenaeracdeocribed-Io .is an automatically variable condenser aerial tive to minute variations in atmospheric pressure. The capacity or the variable condenser is automatically changed with minute variaidons in barometer: pressure and when the condenser it I! electrically connected in the tuning circuit of a signal receiving set, as shown in Figure 1, the capacity of the tuning condensers is automatically changed and the set remains in resonance and signal fading is prevented. Radio broadcasting stations equipped with radio receiving sets provided with this auxiliary pressure sensitive mercury barometer condenser will be able to pick up distant signals with substantially no fading and re-boardcast the same.

The vacuum cells used could be of any dimensions or made of any material which could withstand considerable pressure. A vacuum cell having a diameter of two inches and a height of 3% inches was found to be a convenient size.

Further modifications will be apparent to those skilled in the art and it is desired, therefore, that the invention be limited only by the prior art and the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. That method of substantially compensating for the frequency drift of the carrier wave due to atmospheric pressure changes and received by a wave receiving device, which comprises maintaining the receiving device in resonance with the frequency of the carrier wave in response to atmospheric pressure changes at the wave receiving device.

2. A radio receiver having at least one tunable high frequency circuit comprising reactance of opposite sign, one of which is adjustable, for the selective reception of carrier frequencies throughout a range of frequencies, which frequencies are subject to a shift in frequency in transmission through space due primarily to minor barometric pressure variations, means responsive to the said pressure variations to produce synchronized reactance variations of one sign, and means operatively coupling said lastnamed means in' said tunable circuit in such manner that the tunable circuit, after being tuned to resonance by said adjustable reactance to, a selected one of said carrier frequencies, is

maintained in resonance to that carrier frequency as received due to the synchronized reactance variations therein.

3. In combination with the tuning circuit of a wave receiving set arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to changes in atmosphericpressure, said circuit being provided with a main tuning condenser and an auxiliary automatically variable condenser comprising a conducting portion, and a movable conducting portion insulated from and cooperating with said first mentioned conducting portion and responsive to minute changes in atmospheric pressure for maintaining said tuning circuit in resonance with the frequency of said waves, whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving set.

4. In combination with the tuning circuit of a wave receiving set arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to changes in atmospheric pressurd said circuit being provided with a main tuning condenser and an auxiliary automatically variable condenser comprising a relatively fixed conducting portion, and a second relatively movable conducting portion insulated from and cooperating with said first mentioned portion and responsive to minute aaoonsa atmospheric pressure, said circuit being provided with a. main tuning condenser and an auxiliary automatically variable condenser comprising a conducting portion, and a conductive vacuum cell insulated from and cooperating with said first mentioned conducting portion and responsive to minute changes in atmospheric pressure for maintaining said tuning circuit in resonance with the frequency of said waves, whereby apparent fading of said waves due to frequency drift is substantially. eliminated in said receiving set.

6. In combination with the tuning circuit of a wave receiving set arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to changes in atmospheric pressure, said circuit being providedwith a main tuning condenser and an auxiliary automatically variable condenser comprising a conducting portion, and a conductive vacuum cell insulated from and cooperating with said first mentioned conducting portion and responsive to minute changes in atmospheric pressure for maintaining said tuning circuit in resonance with the frequency of said waves, whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving set, and spring means cooperating with said vacuum cell to prevent collapse thereof.

7. In combination with a wave receiving system of the superheterodyne type arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to atmospheric pressure changes, said system comprising a tunable radio frequency circuit, a tunable first detector circuit and a tunable oscill'ator circuit, each circuit having a main tunlng condenser; an auxiliary automatically variable condenser comprising three conducting plates insulated from each other and each connected respectively to one of said circuits, and a movable conducting portion insulated from said three plates and cooperating therewith and connected to said tunable circuits and responsive to minute changes in atmospheric pressure for maintaining said radio frequency and first detector circuits in resonance with the frequency of said received waves and proportionately changing the frequency of ,the oscillator circuit, whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving system.

8. In combination with a wave receiving system arranged to. receive waves transmitted through space from a remote point and subject to frequency drift due to atmospheric pressure changes, said system comprising a plurality of tuning circuits each having a main tuning condenser an auxiliary automatically variable condenser comprising a plurality of conducting plates insulated from each other and each being respectively connected to one of said tuning circuits, and a movable conducting portion insulated from said plurality of plates and coop crating therewith and connected to said tuning circuits and responsive to minute changes in atmospheric pressure for simultaneously maintaining said tuning circuits in resonance with the frequency of said received waves, whereby apparent fading of said waves due to frequency drift is substantially eliminated in saidroceiv-- umn, and carried by said tube, eachof said plates being respectively connected to each of said tuning circuits and coperating with said mercury column which is connected to said tuning circuits and to maintain said tuning circuits in resonance with the frequency of said received waves in response to movement of said mercury column due to changes in atmospheric pressure, whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving system.

10. In combination with the tuning circuit of a wave receiving set arranged to receive waves transmitted through space froma remote point and subject to frequency drift due to changes in atmospheric pressure, said circuit being provided with a main tuning condenser and an auxiliary automatically variable condenser comprising a' conducting portion, a movable conducting portion insulated from and cooperating with said first mentioned conducting portion and responsive to minute changes in atmospheric pressure for maintaining said tuning circuit in. resonance with .the frequency of said waves, whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving set, and manually operated adjusting means for initially selecting thecapacity of said auxiliary condenser. J

-11. In the operation of a. receiving device hav- I ing a tuning circuit for receiving waves transthe tuning circuit in response to-minute variamitted through space from a remote point, that method of substantially eliminating the apparent fading of said waves due to .frequency shift caused by atmospheric pressure changes, which comprises automatically varying the reactance of the tuning circuit in response to minute varia-'- tions in atmospheric pressure to maintain said tuning circuit resonant to the frequency of the received waves.

12. In the operation of a receiving device having a tuning circuit for receiving waves transmitted through space from a remote point, that method of substantially eliminating the apparent fading of said waves due to frequency shift caused by atmospheric pressure changes, which comprises automatically varying the capacity of tions in atmospheric pressure to maintain the tuning circuit resonant to the frequency of the received waves.

13. In combination with the tuning circuit of a wave receiving device arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to changes in atmospheric pressure. an automatically variable reactance device responsive to minute changes in atmospheric pressure for maintaining said tuning circuit in resonance with the frequency of said received waves. whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving device.

14. In combination with the tuning circuit of a wave receiving device arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to atmospheric pressure changes, an automatically variable reactance device responsive to variations in atmospheric pressure of less than 0.02 inch of mercury for maintaining said tuning circuit in resonance with the frequency of said received waves, whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving device.

15. In combination with-the tuning circuit of a wave. receiving device arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to atmospheric pressure changes, a main tuning. reactance device, an auxiliary automatically varmble reactance device responsive to variations in atmospheric pressure of less than 0.02 inch of mercury for maintaining said tuning circuit in resonance with the frequency of said received waves, whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving device.

16. In combination with thetuning circuit of a wave receiving device arranged to receive waves transmitted through space from a remote point and subiem to frequency drift due to atmospheric pressure changes, an automatically variable condenser responsive to variations in atmospheric pressure of less than 0.02 inch of mercury for maintaining said tuning circuit in resonance with the frequency of said received waves, whereby apparent fading of said waves due to frequency drift is substantially eliminated in said receiving device.

17. In combination with the tuning circuit of a wave receiving device arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to atmospheric pressure changes, a main tuning reactance device, an auxiliary automatically variable condenser responsive to variations in atmospheric maintaining said tuning circuit in resonance with ,the frequency of said received waves, whereby apparent fading of'said waves due to frequency drift is substantially eliminated in said receiving device, E

18. In combination with the tuning circuit of a wave receiving device arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to changes in atmospheric pressure, a main tuning condenser for tuning said circuit to the frequency of said received waves, and an auxiliary automatically variable tuning-condenser in parallel with said main condenser and responsive to minute variations in atmospheric pressure for maintaining fading of said waves due to frequency drift is substantially eliminated insaid receiving device. 19. In combination with the tuning circuit of a wave receiving device arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to changes in pressure of less than 0.02 inch of mercury for said tuning circuit in resonance with the frequency of said received waves, whereby apparent atmospheric pressure, a main timing reactance II cy drift is substantially eliminated in saidre- Y ceiving device.

20. In a wave receiving device, a tuning circuitarranged to receive wavestransmitted through space from a remote point-and subjectsto frequency drift due to changes in. atmospheric .pressure, said circuit including tuning meansadaptod to be adjusted to tune-said circuit to any frequency within the range for which the receiving device is intended; and an auxiliary variable reactance device responsive to minute variations in atmospheric pressure for automatically altering the frequency to which the circuit is initially tuned so that said circuit is maintained in resonance with the frequency of said received waves as their frequency drifts, said automatic alterations being a small fraction of the change that the adjustable tuning means can produce, whereby apparent fading of said received waves due to frequency drift is substantially eliminated in said receiving device. a

21. In a wave receiving device. a tuning circult arranged to receive waves transmitted through space froma remote point and subject to frequency drift due to changes in atmospheric pressure, said circuit including tuning means adapted to be adjusted to tune said circuit to any frequency within the range for which the receiving device is intended, and an auxiliary variablecondenser responsive to minute variations in atmospheric pressure for automatically altering the frequency to which the circuit is initially tuned so that said circuit is maintained in resonancewith the frequencyof said receivedwaves as their frequency drifts-said automatic alterations being a small fraction of the change that the ad- Justable tuning means-can; produce, whereby ap parent fading of said received waves due to frequency drift is substantially eliminated in said receiving device.

22. In combination with a tuning circuit of a wave receiving device arranged to receive waves transmitted through space from a remote point and subject to frequency drift due to changes in atmospheric pressure, means responsive to changes in atmospheric pressure for maintaining said circuit in resonance with the frequency of said received waves, whereby apparent fading of" said waves is subtantially eliminated in said receiving device.

LEWIS D. ECKARD.

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