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Patented 'Dec. 3, 1946 ' 2,411,853 _ UNITED STATE 3 PATENT orifice; ~; PHOTO RADIO SIGNALING BY‘FREQUENCY -' MODULATION 1 - > ~ James L. Finch, East Rockaway; N. Y, assignor'i to Radio Corporation of America, a. corpora tion of Delaware VApplication July 24, 1941, Serial No. 403,821 - 11 Claims. (01. 178-6) v. _ 1 I propose .to transmit during this period a selected. This application discloses a new and improved frequency ‘corresponding .to some de?nite pic-1 method of and means for transmission and re ture ‘shade, preferably black or white or some ception of photo radio subject matter by modu de?nite frequency which would be called super lating the frequency of a carrier wave in direct black or super-white. " . ' y ' proportion to the density or shading of the photo - In describing my invention in detail reference radio subject matter being scanned, transmitting will be made to the attached drawings'wherein the same and receiving the same. Figure '1 illustrates somewhat diagrammatically, J vIn k'novvn'systemslof photo radio transmission the essential elements, of a transmitter arranged of-the type described above any variation in the 10 in accordance with my invention; Figure 2 illus frequency adjustment of the transmitter circuits trates a receiver arranged in accordance with my may result in an error in the received photo'- radio invention to receive the transmission from the matter. Should the receiver adjustment drift, transmitter ‘of Figure land to be controlled .by then the picture may appear darker or lighter the said de?nite frequency transmitted at the on the average than the original. Similarly, if picture or subject, margin; Figure 1a, illustrates the transmitter frequency drifts a like error re a modi?cation of, a portion of the transmitter-of sults. It is conceivable that circuits of high ac Figure 1; Figure 3 illustratesthe motor, com-i curacy could be arranged for use both at the mutators, etc., of Figure 2 and is used in describ transmitting end and receiving end of the circuit ing the mannerin which synchronism is obtained; 50 that these errors could be made negligible. while Figure 4} is a curve illustrating the input and 20 This, of course, involves considerable expense. output of the limiter 14- of Figure 2. v v . My invention relates to a new and improved Referring to Figure 1, the circuits and means means for eliminating this change in contrast ‘or at the left of the dotted line comprises a scanner shade or density in the transmitted picture dur of a well-known type including a drum I on which ing transmission without necessitating the ‘use of a picture or subject to be scanned is mounted. A circuits of such high accuracy that the circuits light 3 cooperates with a diaphragm condensing‘ per se eliminate this error. lens etc. 5, which produces light that is concene In its broadest aspect my invention involves the trated and re?ected from the subject or image to use of a de?nite time interval during the trans a lens vand photo tube arrangement 1. The photo mission for the transmission of a' de?nitev fre-- 30 tube has a sensitive electrode 9 and an anode elec quency used at the receiver to adjust the tune trode -l I- connected in a circuit across the grid thereof to prevent changes in the picture or sub electrodes of a’ pair of ampli?er tubes l8 andg20, ject weight. ‘In a preferred modi?cation my sys the grid electrodes of which are also excited by tem makes use of a portion of the margin of the carrier waves to be modulated impressed on the photo radio subject matter and transmits then a primary winding of a transformer Tl . The photo de?nite frequency for receiver control purposes. "’ tube ‘controls the current through resistances l4 This transmission may take place as stated‘ above and I6 and consequently the bias on tubes l8 and at the picture or subject margin and is applicable 20. The cathodes and grids of tubes [8- and-2i] to all scanning systems known today, such as, are connected to points along the potentiometer for ‘example, those wherein the drum rotates at resistance as shown. I The cam 60 on the drum, a fairly high speed and the scanning element and ‘contacts BI and 62 actuated therefrom and passes along the drum axis once per picture or described more in detail later, controls a circuit the systems wherein the drum rotates at a lower including resistance 64 in series with electrodes speed and the scanning element passes back and < 9 and H. ‘For the ‘present assumethis contact is forth along the drum axis a large number of ' closed and resistance 64 is shorted. The modu times per rotation of the drum. In the former lator is of the nature of an unbalanced modulator case the margin at which a de?nite ‘frequency is wherein the carrier tone is applied in push-push transmitted falls along the axis-of the drum. In and the bias potential vas controlled by scanning the second type of scanner means is provided for is applied to the grids l1 and i9 in push-pull. ’ sending the de?nite frequency at one or both ends The modulated carrier is supplied from the output of excursions of the scanning element along the ' electrodes of tubes l8 and :20 to the control grids axis of the drum, or vice versa. At the‘ receiv of a double triode ampli?er '22 and thence to the ing end the said de?nite frequency received dur primary winding of a ‘transformer T2. The ar ing this margin intervalis used for automatically rangement- includingthe tubes l8 and 20 is sim- correcting the receiveradjustment to follow'any; ilar many respects tqwhat isknown as an un frequency variation at the transmitter or receiver; 2,41 1,858 balanced modulator, the grids I1 and I9 being 4 excited in phase by potentials impressed on the the other from resonance at the generated fre secondary windings of transformer TI connected quency the voltage supplied to GI may be made push-push, and in push-pull relation by potentials .to advance or retard substantially 90 degrees which vary and are impressed on the grids I1 and with respect to the generated voltage originally I9 due to the action of the photo tube electrodes assumed to be on GI. The biasing voltage on 9 and II, the current through which is in turn grid 4| is varied in accordance with the modulat controlled by the weight of the subject or pic ing potentials. As this bias voltage is increased, ture on the drum. This system and its opera» the voltage fed back to GI by way of anode 43 tion is well known in the art, and it is believed 10 tuned circuit L2, C3, C4, etc., is decreased, and that additional descriptionthereof at this point vice versa. This voltage fed back to GI tends to is unnecessary. A similar arrangement has been ’- ‘change the frequency of oscillator 44 as other shown on pafe 85 of volume 1, “Radio Facsimile,”v wise determined by crystal 48. The amount of RCA Institutes Technical Press. this change, or frequency modulation is propor The amplitude modulated carrier-is supplied by ' tional to the amount of voltage thus fed back. secondary winding 30 of transformer T2 to ~the The frequency modulated oscillations are im full wave recti?er 36. The recti?er 36 and ap-' pressed on the anode 50 of tube 44 by way of the paratus to the right of the dotted line in Figure _ electron coupling in the tube and appear in tank 1 comprises the essential elements of a frequency circuit 52. The voltages may then be ampli?ed, multiplied and limited as desired in apparatus 54 modulator such as disclosed in Usselman United 20 States application Serial No. 338,838,'?led June and ‘transmitted. I . I _ . 5, 1940, U. 8'. Patent 2,298,437, dated October '13, In accordance with applicant’s‘novel systeman 1942. The full wave‘recti?er 36 has its cathodes additional de?nite frequency is transmitted for 35 connected together as shown and to ‘one ter correcting and synchronizing purposes at the re, minal of a low pass ?lter 38‘. The other termi ceiver. In a preferred modi?cation this is ac nal of this ?lter is connected to a point'ona re complished by means of a cam 69 on the drum I sistance 3| in shunt to the secondary winding‘ 30 which cooperates with, contacts 6| and 62 to in of transformer T2. The low pass ?lter has a pair clude in the circuit across thegrids I1 and I9 of of output terminals connected together by way of tubes I8 and 29 an additional: resistance 64 or as a resistance 39, 'a point on which is connected to 30 much thereof as desired. The modulating volt-, ground by way of a source of biasing potential’ age on the tubes is thus held at a value _corre,-' sponding to a super-black picture shade and visv The potential at the upper terminal of the re such as to modulate the amplitude of the carrierv sistances 39 results from recti?cation of the car-' supplied to TI an additional amount for a short rier modulated in amplitude‘ in accordance with 35 time interval at the picture margins. Thev ,sys-; the scanned subject, and therefore the potential tem is adjusted so that this amplitude modula at the endof 39 corresponds to the picture den? tion represents super-black but the circuit may sity shade or contrast.

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