US2728854A - Cathode ray harmonic filter - Google Patents

Description

Dec. 27, 1955 K. F. Ross 2,7288'54 CATHODE RAY HARMONIC FILTER Filed April 11,-1950 fig. j

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INVENTOR.-`

G LZ) 6 02 y, nella f "gf ma United States Patentrce 2,728,854 CATHODE RAY HARMONIC FILTER Karl F. Ross, Bronx, N. Y.

`Application April 11, 1950, Serial No. 155,205

3 Claims. (Cl. Z50-27) My invention relates toa harmonic filter for electro magnetic waves.

An object of this invention is to provide a harmonic filter designed for waves of high frequency and adapted to be conveniently and continuously adjusted for a displacement of its pass and stop bands Within wide frequency limits.

Another object of the present invention is to provide a filter of the character described wherein the positions. of the pass and stop bands may be instantaneously interchanged. p

A further object of this invention is to provide afrequency discriminator with very sharp cutoff effective where only a single frequency is received.

Still another object of the invention, allied with the preceding one, is to provide a discriminator which will substantially reject all incoming waves except a single, pure sine wave of predetermined frequency.

Yet a further object of the instant invention, .allied with the one immediately preceding, is to provide a frequency discriminator which will also distinguish between pure sine waves of the desired frequency but of different amplitudes and which may be used as a means for separately utilizing or for selectively channeling such waves of different amplitudes.

lt is also an object of my invention to provide, in a cathode ray tube, a novel type of output electrode adapted to be used in a filter of the character set forth above.

` The invention will be described with reference to the accompanying drawing wherein:

Figs. 1 and 2 are two circuit arrangements representing different embodiments of the inventiom'and Figs. 3 through 7 show different output electrodes usable with the arrangement of Fig. 2.

Throughout the drawing, similar elements have been denoted by the same reference numerals prefixed by different hundreds digits identifying the respective figure.

Referring to Fig. l, thereis shown va cathode ray tube 100 comprising a source of electrons's'hown as a cathode 101 and focusing or beam forming means shown as a first anode 102 and a second or accelerating anode 103. The electrodes 101, 102 and 103 derive their potentials from a battery 104 and a potentiometer 105 in series therewith.

Two pairs of deflecting electrodes 106', 106" and 107, 107", both arranged in the same plane (assumed to be the vertical plane of symmetry of the tube 100), receive signals from input terminals S', 108" to which the electrodes 106', 106" are connected directly and the electrodes 107', 107", which are axially spaced from the former, by way of a switch 109 and a delay network 110. Network 110 may consist of one or more low-pass filter sections, dependingupon the amount of phase shift desired, and has been shown as consisting of two such sections, thus giving a phase shift ranging from zero to 360 within the pass band thereof which is the only range of frequencies of interest in this connection; j v

` The beam 111, produced by the electron gun 101- 103, impinges upon an output electrode generally indicated at Patented Dec. 27, 1955 112 and consisting of a dielectric backing 113, a layer 114 of resistance material thereon and a pair of highly conductive terminal members 115', 115" in contact with J that layer at respective ends thereof. Other uses for an electrode of this description have been disclosed in co pending application Ser. No. 155,207, by Phil Cutler and Karl F. Ross, filed on even date herewith.

The terminal members 115', 115" are connected across an output resistor 116, grounded at its center, and to respective output terminals 117', 117".

j The operation of the system of Fig. l is as follows:

Waves of different frequencies and amplitudes are applied to the input terminals 108', 108" and, thereby, to the electrodes 106', 106", thus deflecting the beam 111 in a vertical sweep dependent in its extent rupon the-'instantaneous amplitude of the combined signal. Assumf ing the switch 109 to be open, the beam will produce an output at terminals 117', 117" which will be substantially proportional to the input signal; this will be understood by considering the elements 114, 116 as the four arms of a Wheatstone bridge the four corners of which are given by the terminals 117', 117", the grounded center of resistor 116 and the point of impingement of the beam 111 upon the resistive layer 114. Thus a centering of the beam with respect to electrode 112 will causev the electrons to flow to ground in equal amounts via the upper and the lower half of resistor 116, resulting in a.y zero output signal, whereas deflection of the beam in one j sense or the other will impress a voltage of correspond ing polarity upon the terminals 117', 117". The system of Fig. l will then function as an amplifier and/or as a delay device the delay of which may be varied by changing the velocity of the electrons of the beam, as by displacing the slider of accelerating electrode 103 on potentiometer 105.

When the switch 109 is closed, the beam 111 will be,`

subjected to an additional deflection by means of the electrodes 107', 107". When the frequency of the incomingV wave is such that its phase shift in the network is zero, 360 or any other Whole number of full cyclesth e deflecting voltages on electrodes 106', 106" and 107', 107"` will be in phase, so that the angle of deflection of the beam 111 will be increased as shown at 111a, this in turn resulting in an increase in the amplitude of the output signal. When the frequency of the incoming wave is such that its phase shift in the network 110 is 180 or any other odd number of half cycles, the deecting volti ages will b e in phase opposition resulting, with proper" substantially suppress frequencies for which the phase' shift in network 110 is an odd number of half cyclesV while greatly amplifying those for which ythis shift is a whole number of cycles. The system of Fig. 1 may be modified by the addition of a switch permitting reversal of the connections between Adeflecting electrodes 106',

106" and 107', 107", so asv to enable the filter to pass the first-mentioned group of frequencies while suppressing the last-mentioned ones; also, the delay network 110 may be omitted and the traveling time of the electrons in the suitably lengthened tube relied on to introduce the necessary delay.. Both of these features have been illus-V trated in Fig. 2.

In Fig. 2 the tube has been indicated at zo'athe inputterminals at 208, 208" and the output electrode, several 5 thus allowing the tube 200 to be of cylindrical configura-- tion, A reversing switch 218 connects these electrodes and the input terminals 208', 208" to the second set of deecting electrodes, 217', 217", which the electrons of the beam 211 reach after traversing -a length of tube which in the following shall be vdesignated L.

.it will be noted that, in contradistinction to the arrangement' of Fig. 1, the second set of deflecting electrodes 217', 2117" is positioned at right angles to the first set'- 216a' etc. Assuming that the spacing of output electrode 212 from the second set of deflecting electrodes is such thatY a signal of given intensity will produce the same amount of vertical and of horizontal deflection of the beam 211 at electrode 212, then signal wavesv of different frequencies will produce traces of linear, elliptical and circular configuration as illustrated in Fig. 3.

ln Fig. 3 there is shown an output electrode 312 having the form of an inclined square, or diamond, this electrodefcornprising a resistive layer 314 and conductive terminal strips 315', 315" as well as, preferably, a dielectric backing such as element 113 in Fig. l. An output -resistor 316, grounded at its center, and output terminals 317', 317" are connected across the strips 315', 315" which are inclined at an angle of 45" to the horizontal.

-Let f 'be the `frequency of the incoming wave, v the speed of the electrons, t=1/f the period of oscillation and T :L/ v the time necessary for the electrons to traverse the distance L. Let us also assume that the switch 218 is in its right-hand position, so that the voltage on horizontal deecting electrode 217 (the right-hand electrode when viewed in the direction of electron travel) and on vertical deflecting electrode 21611" (the upper electrode of the pair determining the sense of vertical deflection) is the same.

If for a given frequency f1=1/t1 the time T is equal to or is an integral multiple of tl, then it can be easily shown 'that under the assumed conditions the locus of impingement of the beam 112 will be a line extending at right angles to the strips 315', 315, this will be true for all the frequencies for which fl=v/L, Zv/L, 3v/L etc. Similarly, for the frequencies f2=v/2L, 3v/2L, 5v./2L etc. .the locus of impingement will be a line at right angles to the one referred to, thus lparallel to the stripsr315, 315". For f3=.v/4L, 3v/4L, 5v/4L etc. the locus will be a circle; for #tsv/8L, 7v/8L, 9v/8L, lSv/SL, 17V/8L ete. and neighboring values it will be an ellipse having its major axis extending at right angles to the strips 315', 315"; and for f5=3v/8L, 5v/8L, liv/8L, 13v/8L, 19V/8L etc. and neighboring values it will be .an ellipse having its major axis extending parallel to these strips. All of these traces have been illustrated in Fig. 3 at fl f5, respectively. p

'lt will now be `apparent that a sweep of the beam kat right angles Ito the terminal strips 315', 315 will result in'a maximum signal at output terminals 317', 317" while asweep parallel thereto will have no effect Whatsoever. Thus each frequency will contributeto the output signal only to the extent that its trace on the electrode 312 has -a component perpendicular to the strips'315, 315". These components are a maximum for frequencies fl,- are'progressively smaller for frequencies f4, f3 'and f5 and disappear entirely for the frequencies f2. Thus therefh'a-s-again been provided n harmonic filter whose passfbands `vr(centered on fl) and stop bands (centered onfZ) may be readily varied by changing` the speed of.

quencies ,previously passed and will transmit those pretit viously attenuated.

it will also be understood-that the spacing between pass or stop bands may be increased and the bands more sharply deli-ned by cascading a plurality of filters of the type disclosed, with the value of v/L increasing or decreasing for successive filters according to a binary progression.

'l'he remaining figures show electrodes adapted for use with systems designed to discriminate between a single, pure sine wave of predetermined frequency, on the one hand, and other types of waves, `including or not including, the desired frequency, on the other. Such devices are particularly useful in voice frequency signaling vsystems of telephone circuits wherein it is necessary to guard against false operation of a relay or other switching device by speech waves that happen to include the critical frequency. Referring to Fig. 4, vthere are shown three concentric ring electrodes of highly conductive material, indicated at 41211, 41219 and 412C, respectively. Each of these electrodes is connected to a respective output resistor 416:1, 41615, 416e and a respective output terminal 417a", 4171;", 417C", the latter in turn being connected to grounded terminal 417' by way of respective condensers 4i9a, 419b, 419e.

lt will now be seen that the arrival of a wave consisting of a pure sine wave of frequency f3 will cause the beam to trace a circular path which, depending upon the amplitude of the wave, maybe made to coincide with one of the electrodes 416:1, Iiltb, 416C, thus giving rise to a D.-C. output signal at the corresponding set of terminals. lf the frequency of the Wave has any value other than those listed under the group f3, the beam will only intermittently intersect the electrodes of Fig. 4, thus producing a series of short pulses which will be ineffective to result in any switching operation, being largely shunted to ground through the respective condensers 419a, 419b, and 419C. A similar situation will exist if some other signal is superimposed upon the wave of frequency f3, since then the trace will be displaced .from its concentric position with respect toA the electrodes 412a, 412b and L,llZc.

Fig. 5 shows a single electrode 512 consisting of .a conductive strip inclined at an angleV of 45 to the horizontal and connected to an output resistor 516, the .output terminals 517', 517" being bridged by acondenser From the foregoing it will be understood Vthat'this electrode responds only to a Wave of frequency f2 and substantially rejects all other types of waves. In Vthis case the output signal appearing .at the vterminals 517', 5,17" will be independent of the amplitude of the incoming wave.. v

Fig. 6 shows three concentric electrodes 612a, 6121), 612C similar to the electrodes of Fig. 4 but comprising lrespective annular layers 614:1, 614b, 614C of resistance' material and pairs of diametrically opposite terminal eleof these .terminal elements is grounded by way of a Yrespective output resistor Md-616e' and 616a"-616c",

shunted by a respective condenser 619a-`619c and 6'19a"-619c". The corresponding output terminals are indicated at 617a'--617c' and 617a"-617c".

of the .incoming-wave, rather than ,a D.C. potential. The arrangement of Fig. 6 may, accordingly, be used as a means for individually channeling signal waves of given frequency but different amplitude.

The arrangement of Fig. 7 is similar to that of Fig. 5 in that it comprises a single electrode 712, inclined Aat an angle of 45. This electrode is, however, of a construction analogous to that of electrode 112 in Fig. 1, comprising a resistive layer 714 and terminal elements 715', 715". Each of these terminal elements is grounded by way of a resistor 716', 716" bridged by a condenser 719', 719", respectively, these terminal elements being further connected to output terminals 717', 717".

The system of Fig. 7 will thus reproduce a wave of frequency f2 together with any amplitude variations thereof and may be used in combination with a selective repeater or amplifier for such a wave.

It is to be understood that my invention is not limited to the specific embodiments described and illustrated and that various modications and adaptations are possible without exceeding its'scope. Thus it will be apparent, for example, that delay means other than thosel specically shown may be used in connection therewith, such as, for example, liquid delay lines, transmission lines and the like; also, the electrodes discussed in connection with Figs. 4-7 may be moded to conform, say, to some other of the traces adapted to be described by the beam, e. g. those shown at f4 or f5 in Fig. 3.

The specific electrode configurations shown in Figs. 3-7 have not been claimed in the present patent but, insofar as they appear to be novel, are claimed in my co-pending application Ser. No. 511,627, led May 27, 1955.

I claim:

1. A wave ilter comprising a source of electrons, focusing means forming said electrons into a beam, a source of signal waves, rst and second deecting means positioned along the path of said beam with a spacing such that the transit time for beam electrons between said two deecting means is at least a substantial fraction of an oscillatory period of said signal waves, circuit means applying Waves from said source of signal waves to both of said deflecting means with a substantially frequency independent relative phasing yet with relatively dephased delecting effects upon said beam, the dephasing of said deilecting elects being due to said transit time and varying with the frequency of said signal waves, and target means in the path of said beam shaped and positioned to respond to a deflection of said beam in a direction in References Cited in the le of this patent UNITED STATES PATENTS 1,882,850 Marrison Oct. 18, 1932 1,999,884 Salzberg Apr. 30, 1935 2,118,867 Schlesinger May 31, 1938 2,124,973 Fearing July 26, 1938 2,182,382 Hollmann Dec. 5, 1939 2,239,407 Wagner Apr. 22, 1941 2,263,376 Blumlein Nov. 18, 1941 2,289,319 Stobel July 7, 1942 2,326,877 Mueller Aug. 17, 1943 2,374,666 Cunnil May 1, 1945 2,376,707 McCoy May 22, 1945 2,404,106 Snyder, Jr. July 16, 1946 2,431,488 Larson Nov. 25, 1947 2,449,975 Bishop et al Sept. 28, 1948 2,477,547 Rggen July 26, 1949 2,507,590 Clark May 16, 1950 2,617,078 Van Overbeek Nov. 4, 1952

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