Part 2
Of course, the sending machine and the receiving machines must run in exact synchronism. This synchronous control of the sending and receiving motors is maintained by the vibration of a rather heavy fork at each station, and adjusted to beat together, with such slight automatic correction by radio as may be required to keep all receiving forks in step with the fork of the station which at the moment is sending. It is a very simple and dependable mechanism, by which any number of motors, of any size, separated by any distance, can be made to run in synchronism.
RADIO MOTOR:
Another scheme of the rotary type, perhaps even better adapted to the distant control of large motors, is a small synchronous radio motor driven by power carried by radio from the broadcasting station to the receiving stations. It is, of course, rotated partly by radio power from the distant station, and partly by local current, just as a loudspeaker is operated. These small motors, rotating in synchronism with the motor at the sending station, control the rotation of a larger motor in each receiving camera, and so all stations keep in step.
STROBOSCOPIC LAMP:
Of course, it would be fatal if it were necessary to wait until the picture was developed before it could be discovered that the receiving camera was getting out of control. So a special “neon” lamp is located to shine on a revolving marker on the motor shaft of the receiving instrument, and flashed by the incoming radio signals, which latter bear a definite relation to the rotation of the sending station motor.
SAME WAVE:
It should be noted that the same radio wave carries both the picture frequency which builds up the photograph and the synchronism frequency which controls the motors, and also that it lights the stroboscopic lamp.
MULTIPLE-SIGNAL RADIO:
A further advance step was made when an audible message was added to the same radio wave which carried the picture. This is done by modulating the carrier wave to give audibility, while interrupting the same carrier wave at a frequency far above the audible range, say, two hundred thousand cycles, to make our picture.
By means of this duplex employment of the same radio wave, it is possible to get, for example, both the gesture and the voice of an inaugural address; the play and the cheers of a national sport; or the acting and song of grand opera.
Perhaps it might be explained that synchronism in visual-audible radio reception is accomplished by the simple expedient of keeping the radio picture “framed,” exactly as this is done in the motion picture theatre.
But continuing the description of the still picture processes a little further, before taking up Radio Vision and Radio Movies, it might be added that while photographs by radio is the more interesting and impressive process, there is little doubt but that radio photo letters will be of much greater immediate service in business.
Commerce, like an army, can go forward no faster than its means of communication. The history of industrial advance in all ages shows that with every addition to communication facilities the volume of business has increased. Obviously a third electrical means of communication will enlarge business, and speed up commerce and industry.
As an aid in national defense the chief of staff of the Signal Corps of the Army, in a recently published report to the Secretary of War, said (_Washington Star_, November 22, 1924):
“Looking into the future of signal communication for a moment, it appears that the basic method of breaking messages up into words, words into letters, letters into dots-and-dashes, and then passing these through the wrist of an operator, as has been the practice since Morse’s fundamental invention of the electric telegraph, seems to be nearing the end of a cycle. Mechanical transmitters with higher speed qualities are becoming stabilized and American invention seems to be making further and rapid progress in associating photography with radio, which bids fair to revolutionize fundamental methods of transmission.
“The message of the future, whether it be written, printed, of mixed with diagrams and photographs, including the signature of the sender, will, it seems certain, soon be transmitted photographically by radio frequency at a rate tens of times faster than was ever possible by the dot-and-dash methods of hand transmission.
“Military messages of the future, particularly in active operations, may contain diagrams and sketches, or even entire sheets of maps, all transmitted as part of the same message and by means of which detection or listening-in will be reduced to a very low minimum.”
The author suggests that it might be added that the newcomer, the radio photogram, has merits distinctly its own, e. g.:
(1) It is autographically authentic; (2) it is photographically accurate; (3) it is potentially very rapid; (4) it is little effected by static; (5) it is not effected by storms; and (6) it is automatic and tireless.
It can also be used to enlarge the individual newspaper’s influence and prestige by the establishment of photostat branch printing plants at strategic points, like summer camps, and winter resorts, and at ridiculously little cost.
Such copies of the news, financial and market report pages of the paper could be distributed in these distant places before they could possibly appear on the streets of the home city of the paper.
Of course, produce market reports, stock market news, and similar matter could be so distributed very much quicker than could be done by any other system, certainly so to the farmer and gardener.
RADIO VISION:
Radio Photographs and Radio Vision, when both are done by the flat-plate method, are identical in principle, the difference being only in the speed of the apparatus, with such modification in the apparatus as will permit of the required speed.
Just as in the Radio Photograph the picture surface of the Radio Vision is covered with a small spot of light moving over the picture surface in successive parallel lines, with the light value of the lines changed by the incoming radio signals to conform to a given order, the order being controlled by the distant scene at the sending station.
And as the whole picture surface is covered in one-twelfth to one-sixteenth of a second, persistence of vision of the human eye is sufficient to get the picture from the white receiving screen—a photographic plate is not necessary.
When the machine of Radio Vision is turned over slowly, the little spot of light on the screen which makes up the picture looks for all the world like a tiny, twinkling star as it travels across the white surface of the screen in adjacent parallel lines, changing in light value to correspond in position and intensity to the light values of the scene before the lens at the broadcasting station.
But when the machine is speeded up until the succession of lines recur with a frequency which deceives the eye into the belief that it sees _all_ these lines _all_ the time, then a picture suddenly flashes out on the white screen in all the glory of its pantomime mystery.
To accomplish this, the apparatus must be speeded up until a whole picture can be assembled on the screen, say, in one-sixteenth of a second, to be seen by the eye directly.
It was necessary to modify the Radio Photo apparatus to permit this increase in speed. So a lens disc is substituted for the fast pair of prismatic plates. Each lens draws a line while the relatively slow rotation of the prismatic plates distributes the lines over the whole picture surface, just exactly as the plates do in the Radio Photo Camera.
The Radio Vision receiving set and the Radio Movies set are identical, and one may, therefore, see in one’s home what is happening in a distant place, an inaugural parade, football, baseball, or polo game (and we call it Radio Vision); or one may see the motion picture taken from the screen of a distant theatre (and we call it Radio Movies).
The Radio Vision receiving set, as now designed, is very simple; namely, a mahogany box, or small lidded cabinet, containing, beside the radio receiving set and a loudspeaker, only a small motor rotating a pair of glass discs, and a miniature, high frequency lamp for outlining the pantomime picture on a small motion picture screen in the raised lid of the cabinet, synchronism being maintained by the simple expedient of “framing” the picture on the screen exactly as this is done in a moving picture theatre.
The author wishes to acknowledge his indebtedness to his friend, Professor D. McFarlan Moore, for a word name for this new device, i.e., “telorama” for the radio vision instrument, and “teloramaphone” for the instrument when it includes simultaneous reproduction of the music or sound accompanying the living scene.
[Illustration: COL. PAUL HENDERSON, OCTOBER 1, 1924. ASSISTANT POSTMASTER GENERAL, WASHINGTON, D.C. MY DEAR COL. HENDERSON:—THIS IS AN EXAMPLE OF OUR NEW RADIO-PHOTO LETTER, A METHOD OF TRANSMITTING MESSAGES BY RADIO INSTEAD OF BY STEAMSHIP. WASHINGTON TO PANAMA IN FIVE MINUTES. IT HAS THE AUTHENTIC CHARACTER OF AN AUTOGRAPHED LETTER, AND THE SPEED OF RADIO. IT IS THE BEGINNING OF A RADIO SERVICE TO THE EYE, WHERE HERETOFORE RADIO HAS BEEN AN ADDRESS TO THE EAR ONLY. WILL THE TIME SOON COME WHEN THE POST OFFICE DEPARTMENT WILL DELIVER BY RADIO PHOTOGRAPHIC COPIES OF OUR BUSINESS LETTERS AT THE SPEED OF LIGHT RATHER THAN THE LAGGARD DELIVERY OF THE ORIGINALS BY MAIL-PLANE. SUCH AN EXCHANGE OF INTELLIGENCE WOULD WONDERFULLY SPEED UP INDUSTRY BECAUSE, LIKE AN ARMY, INDUSTRY CAN GO NO FASTER THAN ITS MEANS OF COMMUNICATION. Jenkins]
COL. PAUL HENDERSON, OCTOBER 1, 1924. ASSISTANT POSTMASTER GENERAL, WASHINGTON, D.C.
MY DEAR COL. HENDERSON:—THIS IS AN EXAMPLE OF OUR NEW RADIO-PHOTO LETTER, A METHOD OF TRANSMITTING MESSAGES BY RADIO INSTEAD OF BY STEAMSHIP. WASHINGTON TO PANAMA IN FIVE MINUTES. IT HAS THE AUTHENTIC CHARACTER OF AN AUTOGRAPHED LETTER, AND THE SPEED OF RADIO. IT IS THE BEGINNING OF A RADIO SERVICE TO THE EYE, WHERE HERETOFORE RADIO HAS BEEN AN ADDRESS TO THE EAR ONLY. WILL THE TIME SOON COME WHEN THE POST OFFICE DEPARTMENT WILL DELIVER BY RADIO PHOTOGRAPHIC COPIES OF OUR BUSINESS LETTERS AT THE SPEED OF LIGHT RATHER THAN THE LAGGARD DELIVERY OF THE ORIGINALS BY MAIL-PLANE. SUCH AN EXCHANGE OF INTELLIGENCE WOULD WONDERFULLY SPEED UP INDUSTRY BECAUSE, LIKE AN ARMY, INDUSTRY CAN GO NO FASTER THAN ITS MEANS OF COMMUNICATION.
Jenkins
[Illustration: Maj. Mauborgne, Washington When a radio message is received as a photo copy of an autographed order, it is known to be authentic and can be obeyed at once. In war this is vital. Combined with simplicity, ruggedness and speed the radio photo deserves attention. Jenkins Oct. 20, 1924.]
Maj. Mauborgne, Washington When a radio message is received as a photo copy of an autographed order, it is known to be authentic and can be obeyed at once. In war this is vital. Combined with simplicity, ruggedness and speed the radio photo deserves attention. Jenkins Oct. 20, 1924.
[Illustration: [Photographs]]
[Illustration: [Photographs]]
RADIO SERVICE TO THE EYE:
Since the initiation of broadcasting, a veritable army of engineers have been devoting themselves to the development of radio as a service to the ear.
The author for several years has been, rather lonesomely, devoting his efforts to the development of radio as a service to the eye.
Incidentally it is suggested that there are undreamed of possibilities in radio in the unlimited frequencies above audibility, in which speed transmission is greatly accelerated by the tolerance of eyesight, not possible in an appeal to the ear. Witness, the motion picture theatre screen upon which a picture is taken off and put back again forty-eight times per second without discovery by the eye; while the slightest error in a note in the orchestra is detected at once and grates harshly on the ear.
Just as the motion picture depends for success on the fact that the eye is easily deceived, so in Radio Vision the eye is fooled into the belief that it sees the radio picture as a whole, though in fact the eye sees at any one moment only the tiny spot of light by which, with almost lightning like speed, the picture is made up.
Audio radio engineers have been working in the very limited audio-frequency band below, say, ten thousand cycles, whereas the workable range where light instead of sound is employed goes away up to millions of cycles. It is confidently predicted that the next great development in radio is in this area.
When the “teloramaphone” is made generally available, then pictures at the fireside sent from distant world points will be the daily source of news; the daily instructional class; and the evening’s entertainment; and equally the long day of the sick and shut-ins will be more endurable, and life in the far places less lonely, for the flight of radio is not hindered by rain, or storm, or snow blockades.
MECHANISMS EMPLOYED:
The successful study of the problem of the transmission of light effects electrically (vision, pictures, light signals, etc.) might well begin with the division of the subject into its elements and sub-elements.
The major division is, naturally, into (_a_) the sending station apparatus; and (_b_) the receiving station apparatus. A great variety of devices have been invented for analysis of the picture at the sending station, and the translation of the light values (which make up the picture) into electrical modulation; and likewise a variety of methods for receiving these electrical signals at a distant place (or places) and there changing the electrical modulations back into light values with which the picture is built up.
SENDING MACHINES—ZINC ETCHING:
Before the refinement of light sensitive cells, actual electrical contact was oftenest employed in sending the impulses which represented light gradations in the picture.
Usually, therefore, a zinc etching of a pen and ink picture was made, and curved into a cylinder. This picture cylinder was then slipped onto a rotating mandril, which was also moved axially by a screw thread on the mandril shaft; or the cylinder rotated and a contact arm moved along by the screw, like the old wax cylinder phonograph.
A delicately suspended arm, moved along by the screw as just described and carrying, instead of the phonograph sound box, a very small and smooth point which was lifted by the high parts of the zinc etched picture. When so lifted the arm makes electrical contact with an adjustable point and current is put into the inter-station wire circuit.
By this means the values of the picture are converted into corresponding duration values of an electric current, and put onto a wire connecting the sending machine with a distant receiving machine (described in detail later in the text).
It will thus be seen that the electric impulses sent out over a wire attached to the contact point represent the value of the light and dark portions of the picture.
The electric impulses are similar to letter-code dots-and-dashes, for the picture actually opens and closes the circuit, like a telegraph key, the dark portions of the picture sending dashes and the light portions of the picture sending dots. With the point set at one end of the cylinder, and the contact arm advancing longitudinally by reason of the thread on the shaft, the point traverses a spiral around the cylinder until the whole picture is covered.
SWELLED GELATINE PRINT:
In another process a swelled gelatine picture print was used to raise and lower the contact-making arm, and a carbon contact button was employed, but otherwise the sending machine was much the same.
FILLED-IN HALFTONES:
Somewhat later halftones of photos were available, and these were similarly bent into cylinders. The interstices between the metal points of the halftones were filled with an insulating wax, and the whole smoothed off until the bright metal points (of different size and representing the different values of the picture) were exposed.
When this picture cylinder was rotated under a contact point, the cylinder and the point being parts of an electric circuit, current flowed in the circuit whenever the point touched the metal parts of the picture, but no current flowed when the insulation passed under the point.
Because the point does not jump up and down, but has a smooth surface to ride on, greater speed and accuracy is possible with the filled-in etching.
LIGHT SENSITIVE CELLS:
As is quite generally known there are certain “semi-metals” which have the property of changing their resistence to an electric current when light falls thereon.
Of this group selenium is typical, although there are several others, thallium, strontium, barium, etc.
More recently it was discovered that some of the rarer alkali metals had the property, under certain conditions, of actually converting light into electric current. In this group are potassium, sodium, caesium, rubidium, etc.
These light sensitive cells vary the electric current quite accurately in proportion to the intensity of the light falling thereon, and when available were quickly seized upon by the workers in “pictures-by-electricity.”
When these light sensitive cells were employed, a modification of the previous picture-translating methods and mechanisms was made, for now a modulation instead of an interruption of the electric current was possible, the modulation representing the values of the halftones of a picture transparency as well as its blacks and whites.
The rotating cylinder now employed was of glass, around which the picture, on transparent film, was wrapped. Inside the cylinder a light was put to shine through the passing picture film as a minute point of light falling on the light sensitive cell located in a dark box.
Just as in the other cylinder schemes the picture is made to traverse this point of light until the whole picture is converted into electric current of corresponding values, which, as before, can be put on a wire, or can be made to modulate a radio wave.
PERFORATED PAPER STRIPS:
One of the oddities of picture analytical translation consists of running a perforated paper strip between a source of light and a light sensitive cell, the paper ribbon perforated with a series of groups of holes.
It is intended that the number of holes in successive groups along the ribbon shall represent successive values of light in the different parts of the picture to be transmitted.
While it is possible to perforate such a ribbon it is quite likely that the experienced engineer would adopt some of the simpler forms of picture translation, for there are enough of them which may be used without hesitation, such basic patents as have ever existed having long since expired.
An unusual scheme consists in writing the message in ink made of saltpeter, and then setting fire to the ink line. The ink line of the message burns itself out leaving the paper intact. Thereupon the paper is carefully laid on the metal cylinder of the sending machine, or on “silver paper” which is put on the sending cylinder. The contact point drops through the burnt lines making contact, and the out-going signals, received on a like cylinder at a distant station, make a duplicate of the original message.
A more satisfactory scheme is to put a thin coating of hard wax on a thin sheet of metal, or metal coated papers. These sheets as wanted are laid on an electric hot-plate and the message, picture, or sketch, is written through the warm wax coating with a lead pencil or stylus. Then the paper with its message etched therein, is wrapped around the sending cylinder and rotated under the contact-making finger, which sends out the electrical impulses.
One may also take the sketch, line drawing, or pen picture, to the zinc etcher (halftone engraving plant), and have him make a print on very thin metal, and develop and harden it, but not etch it. This will give a photographically accurate copy. This copy on the metal sheet can then be bent around the cylinder of your sending machine, and sent out by wire or radio, to be received at all stations tuned in. If etched the etching may be filled in with hard wax and this put on the cylinder, and run under the contact finger.
It is possible to write on paper with copper sulphate (blue vitral) solution, for the acidulated line carries the current through the paper to the metal cylinder beneath, and completes the circuit. The acid may even be strong enough to eat through the paper exposing the metal cylinder underneath.
Salt water with a little glycerine to keep it from drying up too fast will also perform.
Another method which has been proposed is to print or write on paper with sticky material, like Japan drier, and sprinkle thereon a fine powdered wax, battery sealing wax, for example. This will stick to the tacky lines and can be melted over a hot plate or in an oven. The melted wax leaves standing lines which will raise a contact-closing pen passing over it. If the lines are sprinkled with metallic powder a double contact pen can be used and the mechanism is still simpler, less delicate, and more dependable.
One of the newer methods of photogram transmission is to use a rotating table, like a talking machine table, with a rectangular piece of paper thereon (tucked under at the corners), from which to send a communication; market bulletins, for example, broadcast by a progressive newspaper to the farmers and truck gardener patrons in their vicinity.
The contact point is advanced from the outer edge to the centre by a spiral cut on the under side of the table; or by a threaded edge of a detachable tabletop and a reducing gear to move the contact arm across the message, or other scheme.
(Of course, the receiving machine should be a duplicate of the sending machine, with suitable receiving surface.)
The bulletin sheet can not be advantageously used to the very centre, any more than a music record can, but this space can be employed by the broadcaster for printed announcements (as music disc records are so used), the receiving paper being furnished by the broadcaster.
But of all the schemes it is very doubtful if any will ever equal the writing of the message or sketch in lead pencil on paper, and rotate it under a two-contact collector. The graphite of the lines makes contact across the twin-blade terminals, effecting the transmitter as would a telegraph key in the circuit.
RECEIVING MACHINES:
Coming now to the design of a suitable receiving machine, it will be found that an even greater variety of schemes have been tried.
INK PEN RECEIVERS:
Upon a rotating and longitudinally moving cylinder, similar to that of the sending machine first described, a paper is put, and upon this paper, as the cylinder rotates, an ink pen, mounted on a pivoted arm, touches intermittently, being drawn down to ink the paper with every incoming electrical impulse, and lifted off the paper by a gentle spring.
CAPILLARY PEN:
In another ink and pen scheme the electric current is passed through a capillary ink tube to make it flow and black the paper; no lifting of the pen arm is necessary.
As the order of these dots-and-dashes is controlled by the impulses put into the line by the picture at the sending station, a picture is built up on the paper on the receiving machine cylinder, a copy of the picture on the cylinder of the sending machine.
ELECTROLYTIC RECEIVERS:
In another and similar scheme a chemically treated paper is put on the cylinder, and upon this, as it rotates, a metallic point is gently pressed.
When the incoming electric current from the sending station passes through the paper under the contact point an electrolysis occurs which appears as a discoloration of the paper.