US1654123A - Frequency selective transmission system - Google Patents

Description

Dec. 27, 1927. 1,654,123

R.-V. 1 HARTLEY FREQUENCY SELECTIVE TRANSMISSION SYSTEM Filed Sept. 50, 1924 4 Sheets-Sheet 1 Mmvran:

1 Afro/1W0 Dec. 27, 1927. 1,654,123

R. V. L. HARTLEY FREQUENCY SELECTIVE TRANSMISSION SYSTEM fi l! A. HARTLEY ATTORNEY Dec. 27,1927. v 1,654,123

R. y. L. HARTLEY FREQUENCY SELECTIVE TRANSMISSION SYSTEM Filed Sept. 50, 1924 I 4 Sheets-Sheet a 5' /A/VEN7'0/?.'

fiALPH-M L. HARTLEY AIME/vb V2 mummlnmuummi Dec- 27 O X R. V. L. HARTLEY FREQUENCY SELECTIVE TRANSMISSION SYSTEM Fild Sept. 30, 1924 "4 Sheets-Sheet 4 FIG. /2.

VI llllllllll II 52 5:; a 67 hrexz/m mm 1/1. flfl/f/gz Patented Dec. 27, 1927.

UNITED STATES PATENT OFFlCE.

RALPH V. L. HARTLEY, 0F SOUTH-ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., CORPORATION OF NEW YORK.

FREQUENCY SELECTIVE TRANSMISSION SYSTEM,

Application filed September30,1924. Serial No. 740,724.

The present invention relates to selective wave transmission such as the transmission and selection of waves of particular frequen cies for desired purposes.

The present invention further relates to vibrating systems and particularly to the generation, translation and control of mechanical vibrations.

It is a particular object of the invention to effect desired frequency selections by means partly or wholly mechanical.

A further object of the invention is to provide for any desired band width of frequency selection by complex mechanical structures.

A further object of the invention is to provide a system of the type indicated which will be simple in construction and ellicient in operation.

llt is a special object of this invention to provide for selecting mechanical vibrations by mechanical wave filters and for converting the vibrations into electrical variations.

A further object is to provide a signal transmitting system capable of selecting mechanical vibrations ofdilferent frequencies representing different signals and converting them into electrical variations for transmission to a. distance.

Electrical filters generally comprise a reiterative series of sections which may be I uniform throughout the entire filter network but which in practice are generally made up of different types to suit the particular filter requirements. Various types of electrical filters'and the theory and design formulae for them are disclosed in the following publications; U. S. patent to Campbell No. 1,227,113, May 22, 1917 and an article by Otto J. Zobel in the Bell System Techni cal Journal for January 1923 Vol. II, No. 1, pages 1 to 16.

The ideal electrical filter would have lumped inductances and capacities free from resistance. Similarly the ideal mechanical filter would have rigid masses andmassless springs connected by massless connections and moving without friction. In practice these conditions can never, of course, be

realized, but in the design of any filter an approach to these conditions may be made.

A field in which the mechanical filter may be used to particular advantage is in carrier wave signaling. The limitations as to the number of channels in such systems are determined by the character of the selective means available. -What is desired is a filter which introduces a uniform loss for frequencies Within the range of a particular channel and a very large loss for frequencies outside that range. It is known that a mechanical vibrator has a very much smaller damping and energy dissipation than the best electrical circuit of practical construction. The entire resonance curve of a tuning fork of one thousand cycle frequency, for example, was found to lie in a frequency; interval of the order of one cycle. This type of selective element realizes the desired condition of low damping Within the resonance-frequency interval and very high loss for a frequency only one or two cycles distant. The fact that the resonance interval is so extremely narrow, however, makes a vibrator of this character practically useless for signal transmission since the frequency components representing the signal are cut off.

According to the invention, a number of mechanical vibrators are combined with appropriate coupling elements to form a filter in which the low damping which is characteristic of this type of vibrator is secured over a considerable frequency range and in which very large losses will be introduced 'for frequencies only slightly outside the trolled in accordance with signals to be sent.

A more complete understanding of the invention may be had from the following detailed description in connection with the accompanying, drawing; in which Figs. 1 to 8 inclusive, show types of mechanical filters corresponding to the electrical filters shown schematically in-the respective Figs. 1 to 8 inclusive;

Figs. 9, 10 and 12 show in schematic form the application of mechanical filters to carrier signaling systems in accordance with the invention; and

Fig. 11 shows a physical embodiment of one form of mechanical filter. v

Referring now to the figures illustrative of the different types of filter, Fig. 1 represents the general case of electrical filter of the transmission type as distinguished from the suppression type. That is, each section is comprised of series inductance L and capacity C in series with each other and shunt inductance Z and capacity 0 in parallel with each other. \Vhen both series and both shunt elements are present in each section the filter transmits two distinct bands of frequencies and greatly attenuates currents of all frequencies except those included in the two bands. The two bands are coalescent or confluent if LC=Z0, and by omitting one of the series elements from each section or one of the shunt elements, or both a series and a shunt element, the filter may be transformed into one of the types shown in the other Figures 2 to 5" inclusive, and may be made to have only a single transmission band having two finite frequency limits or having as one limiting frequency either zero or infinity. Each of these filters is of the transmission type as distinguished from the suppression type which will be defined hereinafter. All this is disclosed in Campbell Patent 1,227,113 to which reference has been made.

In Fig. 1 showing the mechanical analogue of the electrical filter of Fig. 1", the mass M corresponds to the inductance L, the spring K corresponds to the reciprocal of the capacity C, and the coupling elements m and 7c correspond to the elements Z and c. Vibrations to be transmitted are applied at 1 and the output is taken off from 2. Cor responding to current flow through L, the mass M takes up motion from the impressed vibrations, but continued movement of M in one direction is prevented by spring K which stores energy similarly to the accumulation of a charge on condenser C.

In each of the a figures no attempt is made to represent the appearance which the corresponding filter might present in actual practice, for the reason that it is desired to ado ta convention for the figures that will faci itate comparison with the electrical type by emphasizing the positions of the quantities. For instance in Fig. 1*, the elements M, K, may represent a single member which possesses appreciable mass and elasticity such as a tuning fork or single reed. The fork or reed may have either evenly distributed mass or may be weighted so that its mass is partly or principally concentrated at a point along its len th. The property of elasticity is indicated %y the zigzag line. The spring or reed is firmly secured at its lower end and the vibrations applied at 1 are in the direction perpendicular to the plane of the drawing.

Secured to the top of the reed or spring is a pin 10 which passes through a hole in the rod 11 so that rod 11 is free to rotate about pin 10. Suitable collars may be provided on pin 10 to maintain the rod 11 at the desired level. The hole in rod 11 may be elongated to permit pin 10 to move to and fro in a vertical plane perpendicular to the paper and still permit rod 11 to move about pin 10' as a pivot Without elongating or compressing spring 76.

Secured to rod 11 is the coupling mass m (coupling mass shown by a small sphere in each instance). .Mass m is connected to pin 10 by the coupling spring is which preferably has its end fixedrigidly to pin 10.

The ideal case will be approached by concentrating, as far as possible, all of the mass n the spheres and by having the pin 10, rod 11, and springs l: and K as light (massless) as possible.

Just as elements M, K may be embodied as a tuning fork or reed, the elements 11, m, is, may be embodied in a reed having one end fixed to pin 10 and the other end mounted in any suitable manner to allow endwise slipping relative to pin 10 and bending about pin 10, and this reed may have a weight located at a point along its length or may have distributed mass.

In any case where the mass is concentrated it will be obvious to provide a weight which is slidable along the rod or reed.

When sudden movements occur in M, the

mass m tends to remain stationary and the rod 11 in being moved by pin 10 exerts a moment about 11?. as a center d's orting 7c. The mass m is capable of a translatory motion without having to rotate. This effect may be secured by rotatably mounting m on a vertical pin (not shown)' secured to rod 11 or the equivalent reed. A motion is thus communicated to pin 10 and to mass M. As 70 becomes distorted m is constrained to move. With these explanations of the interaction between the elements, the complete operation will follow clearly from that given in connection with Fig. 1.

From the conventions employed in all of the figures, it will be apparent how each of the other types is constructed and operates.

Figs. 6 to 8 show typical forms of supfilter that its attenuation may be made veryhigh at a frequency just outslde of the range of free transmission, and the cut ofl of the lter therefore be made extremely sharp.

The design data for any of the types of filter that have been given may readily be obtained by use of the formulae given in the Campbell patent above referred to or in the article by Zobel. a I

As an example, suppose that from convenience or other considerations it is desired.

Ell

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to build a band pass filter of the type shown in Fig. 3 and that this filter is to have free transmission for all frequencies between 900 andlOOO cycles per second, and high attenuation for all other frequencies and that the mechanical resistancewithin the transmission band is to be dynes/cm./sec., that is, v

such that an alternating sinusoidal force of 30 dynes is required to maintain sinusoidal motion of the moving element with maximum velocity of 1 cm. per second.

Referring to Fig. 3 and to page 42 of the Zobel article it is seen that the type of filter chosen for the example is that correspond ing to Zobelstype V1,. The design formales for the electrical and for the mechanical types are then as follows, remembering that stiffness is the reciprocal of capacity:

Electrical Mechanical trated at the point indicated in the drawing and that the amplitude of vibration is small compared with the distance of the mass from the center of rotation; If the vibrations are such that the mass has appreciable angular displacement, M would need to be expressed in terms of moment of inertia. If thls were the case the stiffness of 7c and K would need to be expressed as moments of force per unit angular displacement.

The structure shown in Fig. 11 illustrates by Way of example only, the appearance which the filter of Fig. 3 may have in actual practice. 1 The reeds may be steel bars or the like firmly clamped at their lower ends between bed pieces 41' and 42. Instead of single reeds, tuning forks, diaphra ms or other vibratory members may be use Secured to the reeds 40 at a suitable point along their length, preferably at their free ends, are the coupling springs 43. By reference to Fig. 3 it 1s seen that. these coupling springs are massless, and hence are as light. as possible, consistent with their re quired stiflness. Reeds A0, however, have mass and are indicated as comparatively. heavy. The mass may be distributed as in the case illustrated, or may be lumped in the form of a weight (not shown) secured t the reed.

In operation the end reed 40 is set into vibration in any suitable manner, such as by the driving magnet 44 connected in any suitable circuit 45 carrying variation currents and the vibrations are transmitted through the coupling springs 43 to the successive reeds 40. The vibrations to which the structure is selective are passed with uniform small attenuation to the output eleinent 46 while vibrations of all other frequencies are damped out. The filter is shown terminating in a mechanical resistance 47 the nature of which will be described more fully in connection with Figs. 9 and 10.

Reference will now .be made to the applications, shown in Figs. 9 and 10 of the mechanical filter to typical signaling systems.

In Fig. 9, the main carrier line ML terminates in three carrier telegraph transmitters T T and T and in three carrier tcle graph receivers R R and R The translfll) III) mitters may be of any suitable type for sending Waves of respective frequencies and keys or relays for controlling the respective waves in accordance With messages to be sent. The frequencies employed by these transmitters are assumed to lie in a higher range than the frequenciesemployed by the otherwise simi lar transmitters at the distant terminal for actuating the receivers R R and R Ac-' The receiving filter LF feeds into an am plifier A which may comprise any number of stages but shown for simplicity as comprising only a single tube of the well known audion type. The amplified received waves representing all three messages actuate elec-- tromagnetic relay 15 causing its armature 16 to vibrate about the centers 17 and 18. These armature vibrations are applied to the three mechanical filters F F and F which serve to filter out and transmit selectively to the vlvspcctiy'e receivers R R and R the parend section may be connected in series with a the input end section of another or other filters of the same type. To be suited to this manner of connection a filter should have an impedance between its input terminals of the same order as the impedance of the load to which it is connected for those frequencies which it is to transmit selectively and this impedance must be high compared with the impedance which it has for other frequencies. These filters are terminated mid-shunt in order to give them the proper terminal impedance.

That the filters F F and F are series connected to the armature 16 may be seen from considering the corresponding electrical filter of Fig. 2. If this filter is assumed to have a mid-shunt termination it Will have as its terminal element a shunt-connected parallel-inductance-ca-pacity of .2Z and g.

e One indicatlon of the tseries connection 18 that'the input end sections of all the filters have the same motion, corresponding to the series current through theend sections of electrical filters so connected.

In the case of filters F F and F vibrations' of the frequency at which the midshunt elements 19 and 20, for example, resonate produce motion of large amplitude in these elements. Vibration of other frequen-- cies results either in displacing the mass 19 or distorting the spring 20 or in both of these effects but does not produce as great moveinent in the end of spring 20 attached to spring 21 as do the currents of resonant frequency. This discriminating action is, 0t course, carried out by all of the other'elemerits of each filter in such manner as to se- The pin 25 in vibrating taps against the downwardly extending armof the lever'26 will be recognized as the analogue of a detector and relay. The rapid tapping by the pin 25 raises weight 28 to open contact 29, and due to the inertia of the lever and weight, the contact is not again closed until the tapping ceases, that is, until the termination of the wave representing the dot or dash impulse.

The damping device 22, 23, 24 aids in giving the filter the desired resistance termmation.

The system of Fig. 10 is similar to that of Fig. 9 except that the filters F F and F are of the type shown in Fig. 3, this type of band filter being adapted for parallel connection, that is, its input terminals may be connected in parallel with the input terminals of another or other filters. A requirement of filters for parallel connection is that each should have an impedance of the same order as the impedance of the load for currents of the frequencies which the filter is to transmit and this impedance must be low compared with the impedance which it has for currents of other frequencies. These filters in Fig. 10 are preferably terminated-mid-series.

Received currents energize relay 15 as in the case of Fig. 9 and cause actuation of its armature. This armature is secured to a lever system the fulcrums of which are at 33, 34, and 36. Attraction of the armature (motion toward the back of the paper) tends to move pin 33 backward in the drawing, pin 34 forward, pin 35 forward, pin 36 backward. It is evident that the motion absorbed by any filter is proportional in some inverse manner to the motion absorbed by the others. For example, if at any instant only the particular vibrations to which F is selective are being received, pin 33 will take up the motion on account of the low impedance of filter F to vibrations of these frequencies, while pins 34, and 36 will remain practically stationary on account of the high impedance offered to these vibrations by filters F and F If only vibrations are received to which filters F and F, are selective, pin 33 remains practically stationary and pins 35 and 36 take up the motion, the link between 35 and 36 oscillating about an imaginary fulcrum somewhere along its length between pins 35 and 36.

The detecting and receiving elements may be identical with those of Fig. 9.

Fig. 12 of the drawin illustrates two carrier telegraph transmit ing channels which lit . dicated at T, for converting the mechanical vibrations into electrical variations for transmission over any desired circuit L which may be the usual multiplex telegraph line. An amplifier A including any desired number or arrangement of vacuum tubes may be included as desired.

The vibrators V and V are shown in the form of notched discs secured to the shaft 51 which is driven from the motor 52. The

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carrier frequency for each channel is determined by the speed of rotation of the shaft 51 and by the number of notches in the discs so that by providingdifferent numbers of 54 serve to apply to the filters F, and F the mechanical vibrations tors V, and V The filters F, and F are of the type indicated in Figs. ,2 and 9. The constants of the filter F may, in manner hereinbefore described, be proportioned so that this filter produced by the vibratransmits vibrations of the frequency generated at V and also transmits a sufficiently wide band of frequencies on either or both sides of the carrier frequency. to enable signaling to be carried out atthe desired speed.

The filter F will have its constants differently proportioned from those of the filter F, so as not to transmit vibrations of the same frequencies as those transmitted by the filter F but to transmit selectively the vibrations generated at V and such other frequencies as are necessary in order to transmit the signals on the corresponding channel.

The translating means T includes the bar 55 and the electromagnet 56. The bar 55 is adapted to be given rotational vibrations about the axis 57, 57 by the output elements 58 and 59 of the respective filters F and F The bar 55, therefore, partakes of vibrations of all of the frequencies selectively transmitted by the filters associated with it. In vibrating, the bar 55 causes the armature 6O of the eleetromagnet 56 to vibrate near the pole of the magnet and to set up corresponding E. M. Ffs in the magnet winding. The

winding should lmve a permanent magnet core or, some other means for establishing a normal'field. The E. M. F.s generated in the winding 56 are applied to the input of the amplifier A and the amplified waves are impressed on the line L.

The filters F and F are illustrated as having their terminal sections connected to the bar 55 in series, as is indicated by the fact thatthe-output end sections of both filters have the same motion corresponding to the current through the end sections of electrlcalfilters so connected. In order to better adapt the terminal impedance of the filters for this type of connection, they are shown terminated mid-shunt, that 1s, the terminal coupling mass and elasticity each have double the values of those of the interme diate sections of the filters. filters may be connected with their terminal sections in parallel with each other and in common to the translating device, in which case the filters should be terminated midseries instead of mid-shunt. A more convenient filter for this form of connection is that of the type shown in Fig, 3 and the manner in which the end sections would be associated with the translating device is, in general, similar to thatemployed in Fig. 10. As pointed out above, the internal impedance of the filters should, in either type of connection, be of the same order of magnitude as the impedance of the load into which they work; 3

With the arrangements as thus far described, when the motor 52 is set into vibra tion at the proper constant speed, vibrations of respectively different frequency are transmitted from the vibrators V, and V continuously through the filters F, and F to the bar 55. In order to control these vibrations in accordance with telegraph signals to be transmitted, stop members 61 and 62 are provided for acting upon an element of the respective filter. These stop members are normally biased by the springs 63 and 64 so that they bear upon the central series element of the filter with sufiicient pressure to arrest the motion ofthis element. So'long as either stop member 61 or 62 is solely under the influence of the biasing springs'therefor, the central element of the corres onding filter is held stationary and no vibrations are transmitted by it from the central element on through the filter to the bar 55. The transmission of the vibrations in each channel may, therefore, be controlled by a1 If desired, the

engagement with the filter element and permitting the vibrations to be freely transmitted through filter F to the bar 55. When key 67 is raised and electromagnet de energized, stop member 61 is brought to bear upon the filter element, causing it to stop vibrating and the corresponding vibrations are cut off from the bar 55. Stop member 62 may be similarly c-ontr0lled by electromagnet 66 and key 68=to control the transmission'of vibrations through filter F What is claimed is:

1. In combination, a source of mechanical vibrations, means .for translating said mechanical vibrations into electrical variations, means to control the application of the mechanical vibrations to the translating means in accordance with signals, and a mechanical frequency selective device interposed between said source and the translating means for freely transmitting tothe translating means vibrations within predetermined frequency limits only.

2. A signal transmitter comprising a plurality of mechanical vibrators of respectively different frequency, a mechanical filter associated with each vibrator to receive from it and to transmit selectively vibrations of its particular frequency, and 'a common means arranged to receive the vibrations transmitted by all of said filters and to translate the vibrations into electrical variations.

3. In combination, a-mechanical vibrator, a device arranged for actuation by vibrations from said vibrator, a mechanical frequency-selective device interposed between the vibrator and the first-mentioned device, and means for acting on the selective device to control application of vibrations to the first-mentioned device.

4. In a transmitting system, a continuously operating vibrator, a mechanical wave filter having an input section arranged to be actuated by said vibrator, and means acting on the wave filter for controlling transmission through it of mechanical vibrations.

5. In a carrier transmitting system, a mechanical element capable of vibration, a plurality of vibrators of different frequencies for imparting vibrations to said element, and means for translating the vibrations of said element into electrical variations.

6. In a carrier transmitting system, a plurality of mechanical vibrators, means to translate the vibrations into electrical waves for transmission, and means fo restricting the vibrationsthat are translated to a fre-.

predetermined frequency .for transmission, means for restricting the vibrations that are translated to a frequency band of predetermined frequency level and Width, and means for controlling said vibrations in accordance with signals.

8. In combination a mechanical wave filter and means for controlling the transmission characteristic of said filter to modulate the vibrations transmitted through the filter in accordance with signals.

9. A plurality of mechanical wave filters for transmitting vibrations of distinct frequency. ranges, unitary means actuated in common by the vibrations transmitted by all of said filters, and means individual to each filter for controlling the application of vibrations to said unitarv means.

10. In a -arrier telegraph svstem, means to generate mechanical vibrations, means to modulate the vibrations in accordance with a telegraph message, a mechanical filter to select the vibrations, and means to translate the modulated and selected vibrations into electrical waves.

11. A wave transmission system comprising means for continuously enerating mechanical vibrations, means or controlling said vibrations in accordance with signals, and means for converting the resultant vibrations into electrical waves.

12. A signal transmission system comprising-means for generating continuous mechanical vibrations of a definite frequency, means for converting said vibrations into electrical variations, means selective of vibrations of said frequency for applying said vibrations to said converting means, and means for controlling the applied vibrations in accordance with signals.

13. A communication system including a continuous source of mechanical vibrations, means for converting said vibrations into electrical variations and means for selecting said vibrations and applying them periodically in accordance with signals to said converting means.

14. In a carrier telegraph system means for constantly generating mechanical vibrations, means to modulate said'vibrations in accordance with telegraph messages, means for selecting said vibrations, means to translate said selected modulated vibrations into electrical waves and means for transmitting the electrical waves to a distant point.

15. A multiplex communication system comprising sources of continuous mechanical vibrations each of said sources being adapted to generate vibrations at a different frequency, means for converting said mechanical vibrations into electrical waves, mechanical filters associated with each of said sources, said filters being selective of the respective frequencies of said sources, means for controlling the selected mechanical vibrations in accordance with signals and means for applying the resultant vibrations to said converting means.

16. A mechanical wave filter comprising a series of elongated vibratable members securely mounted at one end and free to vibrate at the other end, couplingmembers associated with the free ends of the vibratable members for communicating vibrations from one vibratable member to the next, the members of one kind possessing considerable ,mass, and the members of the other kind being capable of considerable distortion and when distorted of forcibly tending to restore to 'undistortedcondition, the structure as a Whole transmit-ting with substantially uniform attenuation vibrations comprising a band of frequencies and highly attenuating and approximately extinguishing vibrations of neighboring frequencies lying outside of said range.

17. A'mechanical Wave filter comprising a plurality of tuned reeds secured at one end to a rigid support and free to vibrate independently, and coupling members associated with the free ends of the reeds for communicating vibrations from one reed to the next in the series, said coupling members offering mechanical impedance to vibrations dependent in amount upon the frequency of the vibrations, said reeds and coupling members cooperating to transmit" from the first through the system and to produce in the last reed of the series vibrations comprising a broader band of frequencies than is comprised in the range of free vibration of any reed of itself.

18. A mechanical wave filter comprising a series of reeds-mounted for independent vibration and yielding means coupling the free ends of said reeds to each other.

19. A mechanical Wave filter comprising a series of reeds mounted to leave free ends capable of independent vibration, yielding members coupling the free ends of said reeds to each other, means to impress vibrations .upon the first reed of the series, and a signaling element actuated by another reed of the series.

20. A selective system comprising a plurality of mechanical filters each composed of a series of vibratable members, and coupling members for communicating vibrations from one vibratable member to another in the series, the elements of said .filters being differently proportioned in the respective filters to determine a different range of frequencies for freely transmitted vibrations for each filter, a common means for applying to all of the filters vibrations of frequencies within their selective transmission ranges and an individual vibration-responsi 3 device operatively associated with an out ut element of each filter. I 21. A selective system according to claim 20, said mechanical filters being terminated adjacent said common means in fractionalsection termination.

- 22. A selective system for mechanicalvibrational energy comprising a' plurality of multi-section mechanical Wave filters each selective to vibrations of a different range of frequencies, a common vibrationally-operating device connected to all of said filters in series so that the element of each filter connected to said device has the same motion in the case of all the filters, the element connected to said device offering in the case of each filter high mechanical impedance to vi-- brations of the frequencies to which the respective filter is selective, and offering lower mechanical impedance to vibrations of other frequencies.

23. A selective system according to claim 22, each filter of which is connected to said common device by a fractional-shunt section giving the filter a terminal impedance of the same order of magnitude as the impedance of said device.

24. A selective system for mechanical vibrational energycomprising a plurality of multi-section mechanical wave filters each selective to vibrations of a different range of frequencies, a common vibrationally-operating device connected to said filters in par allel, said device being connected to an element of each filter so as to divide the vibrational motion among the saidelements, depending upon the frequency of the vibrations, the element connected to said device olfering in the .case of each filter high mechanical impedance to vibrations of all frequencies outside the range to which the re- Speotive filter is selective and offering lower mechanical impedance to vibrations of frequencies Within the selective range of the respective filter.

25. A selective system according to claim 24;, each filter of which is connected to said common device by a fractional-series section giving the filter aterminal impedance of the same order of magnitude asthe impedance of said device.

In Witness whereof, I hereunto subscribe my name this 23 day of September, A. D. 1924.

RALPH V. L. HARTLEY.

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