US1769919A - Electrooptical transmission system - Google Patents

Description

3 Sheets-Sheet 1 Filed April 50. 1929 m at w k o u 88 88 8: 3a Nazca +8. v 2 I e 4 1 $2.. 8% 88 $8 4 8w o "22 88. Ill: $88 28.? 80.8 8 8.3 8 3 8 8 8. 8 38 3 3 I, V 88 -22 8.2.: Ill! 88 82. 8S 2% 8% An was 34a. 2 8 Ill! 8 8.8 83 8.3 8.8 8.8 SEX 8 aw e 2 8 5 8 82 8 3 8 8 8 3 8 8 8 3 32 w- 8 Arm/war July 8, 1930.

F. GRAY ET sLacTao'oPMcAL Tmnsm'ssxou SYSTEM Filed April 30, 1929 '3 Shuts-Sheet 2 E GRAY .A nvvmvmms J R HEFELE July 8, 1930. F. GRAY ET AL ELECTROOPTICAL TRANSMISSION SYSTEM Filed April 30, 1929 3 Shasta-Sheet 3 ecovzwowh QNN 285-82.

E GRAY R. HEFELE J 5 R m w w A 7' TORNE) thereof.

Patented July 8, 1930 umran STATES PATENT OFFlCE c 1mm our an Jon 1:. or m you, x. xi, assrexoas To sum. runnmen mnonsronns, mcoaroaam, or new roux, n.1, a coarona'rron or.

saw you mcraoor'rrcu 'rmsurssron sr'srmr V Application filed April), ma. seen He. $59,211.

This invention relates to signaling and more particularly to television and high speed picture on and vcomposite signal ton.

An object of the invention is to improve the utilization of the uency transmissionbandinvolvedin for such types of traon as televisionand high speed picture ton.

This invention. is'the result of the discovery that when an object or field of view is riodically scanned in a of parallel ines and the light tone values of elemental areas are translated into electric current variations the energy is'largel concentrated in a number of distinct ban' of frequencies between which there is very little useful energy, and

the position of the bands in the frequency spectrum is dependent upon the field scanning frequen and upon the linescanning uen e energy concentrations resultung m and some of the-lower harmonics and in the regions of the line scanmng uency and the lower harmonics latter bands aremade up of a. plurali of frequencies. the prominent ones of w 'ch'difier appaoximately the field scanning frequency. e bands may, for example, have a band width of approximately 20% of the line scanning frequency, in which case the low energy intervening gaps or valleys have a uency band wi t of approximately 80% o the line scanning frequency.

This invention provides means for producing two or more different photoelectric currents in which the bands of energy concentration are'made to occur at different frequen positions for each photoelectric current y separately scanning difierent hne series of elemental areas of a field of view at same circuit or medium;

In case the uencies are near together, as they wzl ild l iz m ordinary telescanning an ordmary'field oc-" cur in the regions of the field scanning fre- 315" E reof photoelectric currents will The different line scanning I vision, two television transmissions which may be com letely se egated at the receiving termina are oss1 1e from the same station over a 'sing e low grade circuit and a single high grade circuit. Where substantiallfy complete electrical segregation of the diferent television transmissions is not required at the receiving terminal a single high grade circuit may be used.

Simultaneous transmissionfrom separate stations or simultaneous two-way operation is ssible I 11 systems in accordance with this invention t e line scanning frequenc and its harmonics follow an arithmetica pro ression, the harmonics bein multiples o the line scanning frequenc ince the line scanning frequencies for t e different hotoelectric currents are different and their armonics differ by a constant, .the harmonics of one photoelectric current have frequency differences different from'that of an other associated photoelectric current an certain of the harmonics which are common multiples of the line scanning frequency of the diflerent erefore in general coincide. frequencies ma be so chosen that coinciding harmonics wil occur only with respe very high unim ortant harmonics which are eliminatedfby filtering action of the line or other transmission apparatus or by spect to 3' photoelectriccurrents that maybe simultaneously transmitted without interferencev overone circuitklioweyer, if some sacrifice in quality of th'cproduced images is permitted this limitation is'lurgelyremoved Methods of operationunder such conditions are subsequentl described. I

A more detai ed description 0 tion follows and is illustrated int e panying drawings. Fig. 1 is a typical current-frequency diagam of the energy concentrations. resulting om ordinary object at a line scanning frequency rate of 1000 cycles per second;

Fig. 2 i -typicalcurrent-frequency diascanning in a series of parallel lines an gram of the energy concentrations resulting from scanning in a series of parallel lines an ordinary object at a line scanning frequency rate of 1044 cycles per second;

Fig. 3 is a typical current-frequency diagram of the energy concentrations resulting from interweaving the energy concentration bands at the different frequencies shown in Fig. 2 above6000 cycles into the gaps between the energy concentration bands in Fig. 1 and also a synchronizing current having a frequency of approximately 2400 cycles per second, all of which are transmitted over a single broad frequency band circuit;

Fig. 4 is a typical current-frequency diagram of the ener y concentration bands below 6000 cycles of Fig. 2 and an interwoven synchronizing current of approximately 2505 cycles per second, all of which are transmitted over a single narrow frequency band transmission circuit;

Fig. 5 is a typical current-frequency diagram of the energy concentrations resulting from scanning in a series of parallel lines an ordinary object at a line scanning frequency rate of 1200 cycles per second; v

Fig. 6 is a general schematic representation of the transmitting terminal apparatus of a. television system arranged in accordance with the invention for simultaneously generating and transmitting a plurality of television currents;

Fig. 7 is a general schematic representation of the receiving terminal apparatus of a television system arranged in accordance with the invention for simultaneously receiving and translating a plurality of television currents into images; and

Fig. 8 is an alternative arrangement of .1. filter network for separating different received television signals.

The typical current-frequency diagrams in Figs. 1 to 5 represent the general characteristics of the distribution of the energy concentrations of photoelectric scanning currents 4 such as are shown for a more limited range of the spectrum in the joint copending application of Frank Gray and John R. Hefele, Serial No. 337,132, filed February 2, 1929, showing typical photoelectric scanning current-frequency curves of a number of different objects both at rest and in motion. The current-frequency diagrams shown herein indicate the position ofthe energy concentrations at difierent frequencies in the frequency band or spectrum over a range up to ap roximately 19,000 cycles per second of di erent photoelectric currents generated in scanning an ordinary object at three different line scanning rates. Current strength is indicated in the direction of the ordinate and frequencies'along the abscissa. Fig. 1 and Fig. 2 are typical current-frequency diagrams of the principal energy concentrations resulting transmission from scanning in a series of parallel lines ordinary objects at field scanning rates of 20 and 20.88 cycles per second and at line scanning rates of 1000 and of 1044 cycles per second, respectively. The employment of dilferent scanning rates causes the energy concentrations to occur at different frequency positions in the photoelectric current frequency spectrum as is shown by a comparison of the two diagrams. centrations resulting from these two different line scanning rates are within 200 cycles up to about 5000 cycles and from that point on up to about 19,000 cycles the relative displacements of the energy concentrations are not less than 200 cycles and consequently these higher frequency bands occupying distinctive positions may be interwoven and simultaneously transmitted over the same circuit without interference. Fig. 3 shows the frequency bands for the two photoelectric currents above 5600 cycles so interwoven and also the lower frequencybands for one of the photoelectric currents, namely, that having a field scanning rate of 20 cycles per second and a line scanning rate of 1000 cycles per second. All of the photoelectric current frequency bands shown in Fig. 3 and a synchronizing frequency of about 2400 cycles are sufficiently separated for transmission without interference over a single circuit and for segregation at the receiving station. The principal lower frequency bands below 5600 cycles resulting from the field scanning rate of 20.88 cycles per second and the line scanning rate of 1044 cycles per second and a synchronizing frequency of about 2505.6 cycles are shown in Fig. 4 and they must be transmitted over a separate circuit or have their frequencies displaced by means of a carrier to a range outside of that shown in Fig. 3 or to low energy gaps therein if they are to be trans mitted without interference on the same circuit with the signal bands shown in Fig. 3.

In one arrangement this invention employs the intervening wide gaps or valleys of low energy in a photoelectric current for the simultaneous transmission of other signals such as a second photoelectric current and synchronizing current insofar as they may be interwoven into mutually exclusive frequency positions as shown in 3. The very low frequency energy concentrations occurring in the region of the picture scanning frequency at about 20 cycles per second and the line scanning frequency and a few of its lower harmonics even though the rates of scanning for the plurality of photoelectric currents are different may not be sufliciently separated to permit all bands being transmitted without interference over the same circuit as heretofore explained. However, in a transmission arrangement em loying two circuits, one of the circuits may he used to transmitonly those frequency bands that The positions of the energy conwould cause interference, and consequently ning disc having 50 uniformly distributed this circuit may be a comparatively low grade apertures and rotated at different field or circuit having a relatively narrow frequenpicture scanning rates such as approximatecy range provided the other circuit is ahlgher ly 20 and 24 revolutions per second, respecgrade one having a frequency range suflicient tively. 1

for the full frequency band or spectrum of A plurality of photoelectric currents may the photoelectric currents. In general, the be simultaneously transmitted over a single arrangement provides for kee' ing' the intermedium and translated into images. When woven frequency bands of w atever origin two or more photoelectric currents having,

of the proper width andpositioning them in energy concentrationbands which coincide 7 the gaps or valleys of low ener in a ph'otoat a few points, common multiples of the electric current orcurrents an transmitting scanning frequencies, are simultaneously as many such separated bands over a single transmitted over the same circuit the chief circuit as may be arranged to occupy separate problem is to segregate each photoelectric frequency positions, thus making possible current andcause each to operate its proper separation at the receivin station of the difterminal apparatus atthe receiving station.

ferent frequency bands. cans for separate- Where frequency bands coincide separation. 1y transmitting and translating into images after transmission over a common medium F the signal currents shown in' the currentby filters is impracticable andthe coinciding frequency diagrams of Fi 3 and Fig. 4 are bands must therefore either beeliminated at subsequently described an are illustrated in the transmitting station or else the-coincid- Fig. 6 and Fig. 7. ing bands permitted to enter the receiving If a separate low ade circuit or a carapparatus as interfering currents. The phorier current as descri ed above is'not used, toelectric currents generated by two different 25 more than one photoelectric current generscanning rates such as shown in Fig.1 and 90 ated by separate rates of scanning may be -Fig; 5 have suflicint relative separation of simultaneously transmitted over the same their energy concentration bands to permit circuit and made to produce images even separation of all butafew of the coinciding though certain of the original ener conbands above the line scanning frequencies,

3 centrations do overla In the followlng se'vand the interference caused by the coinciding 9r,

eral methods of con ning the transmissions bands may not in many cases seriousl affect to one circuit are described. Fig. 5 is a typithe value of the producedimage. A tel evision cal current-frequency dia ram of the energy signal may require no more than twenty-five concentrations resulting om scannin in a of these bands and for ordinary fields shaped 3 series of parallel lines an ordinary ob ect' at as those shown in the copending application 100 a field scanning rate of 24 cycles per second referred to hereinabove, the photoelectric and at a line scanning rate of 1200 cycles per current signals need not include more than second. Comparison of this current-frequenabout eighteen energy concentration bands. cy diagram with that shown in Fig. 1 havin For the scanning rates shown in the current- 40 field scanning rate of 20 cycles per secon frequency diagrams of Fig. 5 and Fig. l the 1m;

and a line scanning rate of 1000 cycles per interference occurs at every 5th or 6th mulsecond shows that energy concentrations tiple of the scanning frequencies, respecwhich are functions of the line scanning rates tively. Most of thelow frequency harmonics of the two coincide at the'jicommonvmultiplein the regions of theqfield or picture scanning frequency positions of 6000, 12,000, 18,000 frequencies will be,about 4- cycles or. mor.

cycles, etc., and'that between these coinciding apart and may be separated after transmis points the relative frequency displacements sion at the receiving station; HQBXQL, oer; of the ener concentrationsare not less than tain efltheseharnioifics will similarly coin- 200"cycles. or allfrequenciesabove the line .cideand causejinterference j gOne method of i" to scanning frequencies. The. field or. picture paztlyehmmatmg thefinterference due to 1 scanningv frequenciesare inthe regions of 20 o I ann al cycles per--second; ;in the diagrams ess such-bands. in all or in all but one or shownin 1 and Fig.1i5,1respectively. In 11 a part of all fthe photoelectric signals at the region d thepicture scanninfg frequenthe-transmittin statign I his v!ill leaveaall cies and immediately above these requencies or all but oneo the ifiages'without certain of certain of their harmonics will coinc'fle'. its 0.0m nents depending upon the arrange- However, the positions of most of the e ergy ment or eliminating overlapping bands. 7 concentrations may obviously be made to v The loss-may produce more or less distortion occur at different locations in thefrequency .in the produced images but the different phoo0 spectrum by choosing diflerent field or pic-,- toelectric currents can be separated at the ture scanning rates and diflerent'line scanreceiving station and the images Wlll in genning rates as illustrated bycomparison of "eral be recognizable and may well serve certhe current-frequency diagrams. The 'photain purposes. A method of using signal I toelectric. energy concentrations shown in CIIITQDQSIII which the overlapping bands are 05 Fig. 1 and Fig. 5'may be obtained by a scan transmitted to the receivmg station may be we rla'pping -or coirieidingbands s to sup if based that a television signal receiv. apparatus badly out ot. synci. a moving mottled or streak .1 1th no image can be distingur; sequently two images can be scanne tl'crcnt rates and the two signals su d for transmission over the same cir nt- .a recognizable images can be produced u it separating the two signal currents at the receiving station. It the mixed signal currents are allowed to operate two light sources behind two sets of moving scanning devices, respectively, each of which moves in synchronism and in phase with one ot the two transmitting scanning devices, then the two receiving devices will reproduce the two original image fields, but each of these images will be reproduced on a moving mottled field resulting from the other television signal being out of synchronism. In an analogous manner, tlie'widely separated bands of the two television signals can be separated by electrical filters and those bands which fall in the same positions of the frequency spectrum can simply be allowed to remain mixed and go to both of the receiving devices. The presence of a few superfluous bands in a television current generating an image will produce as above mentioned a moving motl background but this effect will be less pronounced than in the arrangement above described in which none of the bands are separated before being impressed 'upon the receiving devices. The appearance of the mottled background may be less objectionable if the speeds of rotation of the dittere-nt scanning discs are not exactly in the ratios of integral numbers due to'the fact that a ratio of exact integral numbers may cause a superfluous band of frequencies to give stationary streaks in the field. A departure from such an integral relation will cause the streaks to move. It is therefore preferable not to use in the example given, exactly and 24 revolutions per second of the scanning discs for the two different rates of scanning, but for example, 20 and 24+ rcvolutions per second. To be more exact the speeds of rotation should be such that the highest frequencies involved in the unseparated parts of the two signals do not hear an exact int- ."l ratio to each other. As a matter of Ciltfll operation, such slight variations maynormally occur and no special prov K113 be required for this variation.

Most any desired co picture and of line nning rates may obtained by using a .rllllg discs having the same or different numbers of apertures and rotated at the same or C .rerent speeds. However, other systems scanning than those employing a scani.-....-i.g disc may be used to inatioi'is of field or generate equivalent difierzzt photoelectric currents.

The television transmi in Fig. 6 in general co paratus consisting of tel )aratus, current ampl the photoelectric curren apparatus for two com transmitting units, each 01 c aled at different scanning rates. The two in are connected to a common output network so designed that currents covering a wide frequency range are passed to a high. grade and currents covering a narrow frequency range are passed to a low grade transmission circuit, the frequency distribution of the energy concentrations for the two circuits being as shown in Fig. 3 and Fig. 4, respectively. An object 10 whose image is to be transmitted is periodically scanned in a series of parallel lines by the scanning apparatus 20. An image of the object is focused upon the view ing field of the scanning apparatus by means of a suitable objective lens system 11 and light from elemental areas of the image thus formed is directed by means of the lens system 12 upon the light sensitive cell 30. The scanning arrangement may comprise any suitable device, such as a rotating scanning disc 21 having a row of apertures spirally i station shown terminal ap- .cn scanning apiaratus for vnchronizing photoelectric arranged. An opaque member having an aperture 13 is positioned between the lens 11 and the scanning disc and limits the size of the image field upon the scanning disc so that just one aperture in tip: scanning disc is exposed at any instant, the angular width of the a erture 13 being equal to the angular pitch 0 the apertures in the scanning disc. The scanning disc is driven at suitable speed by means of a driving motor 22. A synchronous alternator 23 mounted on the same shaft with the scanning disc 21 and the driving motor 22 isemployed to maintain synchronism between the transmitting and the receiving scanning apparatus. The photoelectric current generated in the light sensitive element is amplified by suitable vacuum tube am lifiers 40, 50, and 70. The output circuit 0 the light sensitive cell 30 contains a battery 31 and a resistance 33. Battery 31 causes current to flow throu h the resistance 33 which is carried by t e changing excitation of the light sensitive cell. This results in a varying potential across the resistance 33, one side of which is connected to the grid and the other to the filament of the vacuum tube of the amplifier 40. Battery 42 is adjusted to apply a proper negative bias to the grid of the vacuum tube. The output of amplifier 10 is impressed upon the intermediate amplifier whose output is in turn impressed upon succeeding amplifiers. Battery 51 supplies space current for these amplifiers. Any suitable number of stages of amplification may be employed.

The amplified photoelectric current on passbetween the input of the repeating coil 90.

and the other elements in this circuit' for properly matching and adjustin impedances to stabilize theoperatlon o the synchronizing circuit. The television terminal apparatus shown in the lower half of Fig.

6 is identical with that shown in the upper half with the exception thatthe line scan-- ning rate is different, the rate chosenbeing 1044 cycles per second instead of 1000 cycles. The oscillator chronizing current, as ve mentioned for one of the units, has beenchosen as 2400 cycles per second and that for the other unit 2505.6 cycles per second, which bear the same ratio to each other as the line scanning frequencies of 1000 and 1044- cycles er second. Other figures may be used 'ut the ones chosen are such as to cause generation of frequency concentration bands, as shown in the current-frequency diagrams heretofore described and also permit the insertion of the two synchronizing currents in low energy gaps of the photoelectric currents.

The low pass filter 130 has a cutoff frequency at approximately 5600 cycles per second and therefore passes to the transmission line 120 all currents up to 5600 cycles. High passfilter 140'also has a cutoff frequency of .5600 cycles and therefore passes all currents hav ing a frequency above 5600 cyclestorepeating coil 140 and -to transmission line 100.

- This filter does'not operate'in the reverse direction. In this arrangement the operation of these filters is such that all si al currentsbelow 5600 cycles generate by the second television unit are transmitted by transmission line 120 and all of the currents above this frequency are transmitted by transmission line 100.- The transmission line '100 also transmits all signal currents of any frequency originated by the ,first television transmitting apparatus. Transmission line 100 must therefore have a wider frequency- I range. than transmissionline; 12 0. If'the transmission line 100 has a frequenc ran e sufficiently beyond that required transmission of the signaling currents already assigned to it, the sigleials 'assi ed'to transmission line 120 may steppe up by means of a carrier current to frequency regions beyond the other signals and all signals generated by the two, television transenerating the syna ho mitting may be'sent over a single pair of conductors.-

The television receiving. station shownin Fig. -7 in general co v rises terminal apparatus consisting of ltering network for separating and routing the several received signal currents, current amplifying a aratus and synch onously operated television receiving appa tus for-two receiving units.

i pedance of-the output sides of therepeat i g coil'211 or the input side of the repeat- 'e:l7e/nents is .so small in comparison with. the

ing coil 225, that;'the synchronizing current is .drained' outof this circuit. In a specific case,

impedances 221 and222 may comprise inductance and capacity elements,- res ectively. One side of the local receiving sync ronizing circuit -;which leads to the synchronousmo- "tor of the receivin scanning unit240*-i sconnected to one of t e series arms of thefilter network and the other side betweemthe twoj, impedances. The television currents are passed directly through the series armsof this network to the repeatin coil- 225 and intothe filter network 230 w ich passes all frequencies of the order of 20 to 19,000. cycles. This network containsa number of filter elements connected. in multiple. to the incoming circuit. The output side of these filters are connected to 'two output circuits running respectivelyto. the two televisionreceiving units." The transmission line as heretofore explained transmits all of the signal current for one television ima and a large part of the signal current for t e second television"i1mage,""and these filters route each of the twotelevision signals to their respective image producing units. The low pass filter-element 231 transmits frequencies up to 5600 cycles; band-pass filter 232 transmits a' band of frequencies about 200 cycles wide in the region of 6000 cycles; band-pass filter 233 transmits asimilar band in the region of 7000 cycles; and so on up to a band in the regions of 17,000 and 18,000, c cles which are transmitted by band- pa lters 234 and 235, res ective1y., This group of filters passes. all photoelectric current for the televisionimage having a line scanning frequency of 1000 cycles and also a synchronizing current of 2400. cycles. The out ut side of this group of filtersis connec to the television translating apparatus throu h the potentiometer 240 used for regulating t e 11;-

tensity of the television signal. These sig nal currents may be further amplified by the amplifier 250. The circuits must be so arranged that the current through the glow discharge receiving lamp is at all times proportional to the illumination at the transdirect current component must be restored before the changes in light intensity at the receiving station will follow those at the transmitting station. The amplifier 260 provides means for making the necessary adj ustment. The incoming photoelectric signal current whose intensity is'adjusted by means of the potentiometer 240 is impressed upon the grid of the vacuum tube of the amplifier 260. The space current which is provided by the battery 261 is adjusted by the grid biasing voltage of the battery 262. Instead of connecting the glow discharge lamp and the vacuum tube directly in series, a resistance 263 is shunted across the output of the circuit of the vacuum tube across which is set up a potential proportion to the current through the resistance. The receiving lamp 270 is shunted across this resistance. In order to confine the operation of the vacuum tube of the amplifier 260 to the linear part of its characteristic, the biasing battery 271 is connected in series with the lamp so that current through the lamp will go to zero even when a finite current is fiowing through the vacuum tube of the amplifier 260 and it is still on the linear part of its characteristic. For any strength of the alternating current television current determined by the potentiometer 2 l0, the direct current component of the television current may be restored by adjusting the grid biasing battery 262 to such a value that the proper direct current flows through the receiving lamp 270. The viewing field in front of the receiving lamp is defined by the aperture 285 in an'opaque plate positioned in front of the scanning disc281 and in line with the receiving lamp 270. The annular width of the aperture 285 is such that just one aperture inthe scanning disc appears at any instant, the annular width of this aperture being equal to the annular pitch .of the apertures in the scanning disc. The scanning disc at the transmitting and the receiving stations are driven by the direct current motors and held in synchronism and in phase by the alternating current machines in accordance with well established practice. A typical synchroniz- T ing arrangement is shown in the patent of H. M. Stoller et al. No. 1,7 63,909, issued J unc 17 1980. The incoming synchronizing current of approximately 2400 cycles is passed by the filter network 220 to the amplifier 284 which in turn is connected with the synchronous motor 283 associated with the receiving apparatus 280 The energy for driving the scanning disc 281 is supplied by a driving motor 282, synchronism being maintained by the synchronous motor 283 whose input'current is transmitted from the television transmitting station. The filter network 230 as so far described transmits television current for only-one image, namely, that generated by a line scanning rate of 1000 cycles per second. A part of the television signal current for the second image generated by a difierent line scanning rate is also transmitted by the transmission line 100 and this portion of the second signal mustbe segregated and routed to the second television receiving terminal apparatus which is shown in the lower part of-Fig. 7. For this purpose the filter network 230 contains a number of band-pass filters which transmit frequency bands approximately 200 cycles wide and which have mid-frequencies which are multiples of a line scanning frequency of 1044 cycles. The first of these band-pass filters 236 transmits such a band in the region of 6264 cycles, the second band-pass filter 237 transmits a band in the region of 7 308 cycles and so on up to band-pass filter 238 which transmits a band in the region of 18792 cycles. The output circuits of these band-pass filters are all connected to the input circuit of the second television receiving apparatus and the energy concentrations of the television signal having frequencies in the regions of 6264 cycles and above are thus all received from transmissioncircuit 100, while the energy concentrations below this frequency are received over the transmission line 120. The terminal apparatus for producing the second image which is shown in the lower half of Fig. 7 is similar to that already described in the upper half of Fig. 7 with the exception that a filter network similar to network 230 is not required.

An alternative filter network which may be substituted for the filter network 230 is shown in Fig. 8. The dot-dash lines XX and YY in each of these figures indicate the point of connection of the input and output circuits. In the alternative arrange ment the incoming signals are impressed upon a low-pass filter 331 transmitting all frequencies below 5600 cycles and upon a high-pass filter 332 transmitting all frequencies above 5600 cycles. The signal bands above 5600 cycles are impressed upon two harmonic band-pass filter networks capable of passing frequency bands of the desired width and which are-harmonics of a fundamental frequency. The harmoni'c'band-pass V filter 333 passes frequency bands approximately 200 cycles wide and which have mid-:

wide and whic have mid-fre uencie's which are multiples of 1044 cycles. n other words, for example the fre uencies of .the bands transmitted by these i 100 and (n X 1044) ilOOcycIes, re'spec-- tively, n being any whole number; The. low-v 5600 cycles and the harmonic band-pass filteij'i apparatus operated by the television current- -ygenerated'byl'a linescanningff uency or; X1000 cycles, while the hannonimand-pasS- filter 334 which transmits all harmonics {above 5600 cycles in the regions of multiples of 1044 is connected with the second television receiving apparatus,- thus com leting the partial television signal current irectly transmitted over transmission line 120;

The different frequencies used in describing this system as adopted for two separate circuits are t pical and are used primaril to facilitatet e description. Obviousl di ferent scanning rates may be select and the frequency, range of the television current is not necessarily limited to a' ran 0' oil-from 56' to 20,000 cycles and also di erent freuencies from those mentioned may. be used or 'the synchronizin channels. essential requirement is t at the energy concentration bands in the different signals have an proper-separation so that the bands of one signal may be inserted in the low energy bands or gaps of the other signal currents thus making the energy concentrations of the difierent signal currents occur at mutually exclusive frequency positions as far as possible. v The arrangement shown in Figs. 6 and 7 employs two transmission channels, asall energy concentration bands are kept sepan'tran mission but as heretofore ex-P ine a luralityoftelevision signals may be ansrfntteclrover the same circuit provided separation of the imagesahthe receiiv ing terminals is efiected only by a difference in scanning rate,or the two signals are separated,byifilters with-rw ect to all but the interfering frequencies ij. ich are'ia' lljowedtox.

, pass into the receiving circuitsfor the interering frequency bands "of the signals are.

With the first and second of theseplans the low pass filters 130 and the high pass filter 6 are eliminated and the.-

i 140 shown in-Fig; output circuit of 55 .1000 cycles and 120 cycles, sucflr'as shown in ters are (n X 1000) eliminated at the transmitting stations.

the currentfrequen .diagrams of Fig. 1 and Fig. 5, the inter erin frequencies occur' ;at .6000, 12,000, 18,000 cyc es etc., and either such frequencies could be eliminated from both signals or from only one, in the latter case arranging the elimination to alternate between the two signals thus limiting the 6000 band in one signal and the 12,000 band jinthe other andso'on. ,Wh'en only one trans in mission circuit is used for a plurality of tele- 7 pass. filter 331 having a'cut-ofi frequencyof;

vision Signals and separation of'the'imagesatthefi'eceivin g end is efiected entirely by a 33.3 are connected to thetelevision receiving}- diiieren'cepin scanning rates,f.the filter net- 4 work 230 of Fig.5? iseliminated and all tele:

vision signal cu t f nts areimpr'esseduponthe 5 receivin lamps of bothof thefter'minal units.

If thesecond'and'third plans are used the filter network 230 is retained andeach telei vision-current is separated as far as -pra'c-- 'ticable before being'impressed upon the re- .ceiving lamps. of thecurrents mayeitherbegenerate at the trans-- mit ing station and transmitted therefrom an separated at the receiving station as described or a. single synchronizing current may be transmitted and harmonics 'ener'ated therefrom for controlling the di erent receiving units. Further description of in'Odi .fications for usin only one transmission circuit are obvious I m the earher general description of-the principles involved and the detail descriptionof the system shown in *Fi 8.6mm.

- he operation of of the principal ere ments of thesy'stem has been described in more or less-detail inthe foregoing description "of the'app aratus- In the general operation of the system a whole, the light tone values ofline series ofelemental areas of the objects orfields'of view are translated into 10:, difi'erent and'distin'ct photoelectric currents, each having energy concentrations in narrow frequencyf'bands at various predetermined separated frequency positions in the photoelectric current spectrum. A plurality of such photoelectric currents are interwoven either n p Q le x1; a ethernitll such other signaling c'iirrents as'may be re quired s-such as synchronizing currents and... allftra'nsrnitted over a plurality of transmiss'ion cffi cuits or a single transmission circuit. lf tlie e'nerg'y concentration frequency bands which are transmitted: over a single circuit 7 uencies ,as to be mutually exclusiv fthlfi' signals at the receiving sta- 12 1 tion may be separated and impressed upon their respective translating devices by means of electrical filters. If energy concentration have such f bands having frequencies WhlCll are not mu:

tually exclusive are transmitted over the same 2 circuit, the received signals cannot be elec-. tricallyseparated and the produced images contain some distortion caused bys'uch interfaring currentgthoughas heretofore pointed out, 111 cases, such'interferenceis not nchronizing serious. Filter networks at the receiving station are desirable for segregating the various energy concentration bands to permit directing the signal currents to their respective receiving elements so that each band acts as if it had been kept separate throughout its transmission. The direct current and very low frequency components may be eliminated before transmission and restored by local means at the receiving stations, as explained in the description of the system.

This invention in general utilizes the low energy gaps or valleys in the photoelectric signal current and makes possible the utilization of the transmission medium at a greater efiiciency and also makes possible the direct transmission of all signal currents necessary for the operation of a plurality of photoelectric current transmissions over a single transmission circuit. may be from a plurality of scannings at the same station or different stations and all in the same direction over the transmission line or from different stations and inopposite directions. Any plurality 'of scannings at the same station may be of separate objects or of the same object such as might be required for stereoscopic transmission, or even for color transmission where suitable filters or other color selective elements are used with a plurality of channels at both the transmitting and receiving stations. For two-way operation over the same transmission medium, an associated transmitting and receiving station is employed at both terminals.

lVhat is claimed is:

1. The method of signaling which comprises successively scanning line series of elemental areas of a field of view having different tone values, producing from said scanning a composite'electric current containing one or more groups of frequency components of large amplitude, separately scanning other line series of elemental areas at a ditto-rent scanning frequency to produce a second similar composite current, and simultaneously transmitting said currents.

2. The method of signaling which comprises successively scanning line series of elemental areas of a field of view having different tone values, producing from said scanning a composite electric current containing one or more groups of frequency components of largeamplitude, separately scanning other line series of elemental areas at a different scanning frequency to produce a second simi lar composite current, and simultaneously transmitting said currents over the same transmission medium.

3. The method of signaling which comprises successively scanning line series of elemental areas of a field of view having different tone values, producing from-said scan ning a composite electric current containing one or more group of frequency components The television transmission of large amplitude, separately scanning other line series of elemental areas at a diil'crent scanning frequency at the same station to produce a second similar composite current, and simultaneously transmitting said currents.

4. The method of signaling which comprises successively scanning line series of elemental areas of a field of view having different tone values, producing from said scanning a composite electric current containing one or more groups of frequency components of large amplitude, separately s *anning other line series of elemental areasof interposed portions of the said field of view at a different scanning frequency at the same station to produce a second simirar composite electric current, and simultaneously transmitting said currents. V

.5. The method of signaling which comprises successively scanning line series of elemental areas of a field of view having dif ferent tone values, producing from said scanning a composite electric current containing one or more groups of frequencycomponents of large amplitude, separately scanning at different stations line series of elemental areas of different fields of view at different scanning frequencies to produce additional similar composite currents, and simultaneously transmitting the said currents over the same transmission medium,

6. The method of signaling which comprises successively scanning line series of elemental areas of a field of View, having different tone values, producing from said scanning a composite electric current containing one or more groups of frequency components of large amplitude, separately scanning at a different station line series of elemental areas of a field of view at a different scanning frequency to produce a second similar composite current, and simultaneously transmitting the said currents in opposite directions over the same transmission medium.

7. The method of transmission which comprises concurrently generating by different rates of scanning and transmitting a plurality of photoelectric image currents representingthe light tone values of elemental areas of a corresponding plurality of fields of view each extending over a wide band of frequencies, and concurrently transmitting the said currents at least in part over the same transmission medium.

8. The method of transmission which comprises concurrently generating by different rates of scanning and transmitting a plurality of photoelectric image currents representing the light tone values of elemental areas of a corresponding plurality of fields of View each extending over a wide band of frequencies, concurrently generating nonimage currents a nd concurrently transmitting said currents atleast in part over the same transmission medium.

9. The method of characterizing and com positely transmitting a plurality of photoelectric currents, each of which is generated by successively scanning elemental areas of an object whose vima e is to .be produced. which comprises scanning for each photoelectric current generated a different number of elemental areas of a fieldin the same period for scanning fields with different resolutions,

respectively.

11. An electro-optical system comprising terminal transmitting and receiving apparatus, a transmission medium, scanning means for scanning different portions of an image at different fundamental frequencies, respectively, and means for impressing the resulting photoelectric currents having different fundamental frequencies and harmonic fre guencies thereof upon the transmission meium, the different fundamental frequencies and harmonics thereof at least in part occupying different frequency positions in transmission.

12. A two-way electro-opt-ical system comprising terminal transmitting and receiving apparatus, a transmission medium, and means for generating a television current by scanning a field of view at each terminal atv different rates, thereby causing the fundamental frequencies and most harmonics thereof'of the television currents generated at two interconnected terminals to be so displaced that the energy components of the television current generated by one scanning apparatus falls in frequency positions Between the energy components of the other television current.

13. A transmission system comprising means for generating by different rates of scanning a plurality of image currents corresponding to the light tone values of elemental areas of a corresponding number of fields of view, the essential frequency components of eachof said currents being distributed over a wide frequency band and largely occupying substantially mutually exclusive frequency positions in the image current spectrum, and means for concurrently impressing upon a common transmission medium the said essential frequencycomponents of the said' plurality of image currents.

14. A transmission receivin prising means for concurrent y receiving a pluralit of photoelectric image currents, the essentia frequency components of said cur rents in part at least occupying mutually exsystem com elusive frequency ositionsrepresenting the light tone values of elemental areas-of 'a correspondingpluralityof pictures or objects and. occupying a wide band of frequencies, and non-image currents having frequency components occupying non-interfering positions with respect to said image currents, means for separating said image currents and said non-image'currents, and means for separately utilizing said currents. 15. A television receiving system comprising means for concurrently receiving a plurality of televisionimage currents, the essential frequency components of each ofsaid currents occupying muta lly: exclusive fre quency positions and extending over a wide band of frequencies, and synchronizing current occupying a frequency position difier- 1 ent from that of the essential frequency components of said image currents, meansfor separating said synchronizing current from 'said image currents, image producing means for utilizing said ima e currents in the concurrent production 0 a plurality of television images, and means for utiliz' said synchronizing current to control said image producing apparatus. 16. A transmission receivin system comprisin means for concurrent y receiving a plurality of image currents representing the light tone values of elemental areas of a picture or other object, the essential frequency components of saidcurrents occupying mutually exclusive frequency positions in the image current spectrums and extending over a wide band of frequencies, and non-image currents respectively occupying different frequency bands from those occupied by the essential components of the said image currents, and-means for selecting and directin each of said currents into a separate channe 17 An electro-optical system comprising means for successively scanning elemental areas of an object or field at a given rate and generating photo-electric signal current having concentrations of signal energy at a given fundamental frequencyand at multiple frequencies thereof, means for successively scantioned si nal current, means for transmitting all 0 said signal currents over the same transmission medium, and means for separating the components of the different signal currents from each other; Y

18. A photoelectric signaling system comprising means for successively scanning a plurality of fields of view having different tone values, said means comprising apertured scanning discs, each aperture of which scans a line of one of said fields, means controlled by each of said scanning means for generating a composite electric current containinggroups of frequency components of lar e amplitude which are harmonics of the fie d scanning frequency, means for causing the field scanning frequencies and the harmonics thereof generated in scanning each different field of view to occupy at least in part different frequency positions, means for separately generating other currents having a frequency range outside those of said groups, and means for simultaneously impressing all of said currents upon the same transmitting medium.

. 19. A multiple field television system comprising means for successively scanning a plurality of fields of view having varying light tone values, said means comprising scanning elements forsuccessively scanning line series of elemental areas of said fields at different rates, light sensitive means cooperating with said scanning elements, means including said scanning means and said light sensitive means for generating for each of said fields distinctive composite electric currents containing groups of frequency components of large amplitude, each of which are harmonics of the different field scanning frequencies, said groups also containing harmonics of the different line scanning frequencies, means for generating a television synchronizing current having a frequency range outside of the components of those of said groups, means for siu'iultaneously impressing all of said currents upon the same transmitting medium, means for translating all of said composite currents into light, and means for producing images. from each of said composite electric currents comprising scanning means operating at the same field scanning and the same line scanning frequencies as those scanning the different fields of view when generating the said composite currents.

In witness whereof, I hereunto subscribe my name this 24th day of April, 1929.

FRANK GRAY. In witness whereof, I hereunto subscribe my name this 23rd day of April, 1929.

JOHN R. HEFELE.

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