January 1937 Radio-Craft[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles from Radio-Craft.
The ability to generate clean, controlled radio waves at 3 THz in 1937 was about as attainable as putting a man on the moon. That did not stop scientists and engineers from theorizing how to get there and what to do once attained. That's the way science progress happens. An official name had not yet been given to the spectrum realm, but news reporters conjured up the moniker "mystery rays." Even scientists called it the "black gap." Both sound a bit hokey and there is a temptation to poke fun at the renowned technical ignorance of most media types, but no less a science giant as Albert Einstein referred to quantum entanglement as "spooky action at a distance."
The big idea of author W.E. Shrage was to exploit and extend the concept of a cathode ray tube (CRT) to convert streams of electrons into a visual image to use a photosensitive surface to directly convert (no mixing to an IF) terahertz radio waves modulated with audio directly into sound. Only amplification and some filtering would be necessary. I just checked Amazon and no such radio receivers are available, so it is safe to assume the idea never progressed past the conceptual stage. Oh well, on to the next project.
The "black gap" referred to by a well-known scientist, in describing those extremely high frequencies about which we know so little at present, threatens soon to become one of the most important bands of radio communication, if the premises set forth by the author prove to be true. The methods described are, of course, products of the imagination, but ...
W. E. Shrage
It is common knowledge that radio waves, like those of light, are electro magnetic in nature. Expressed in the language of the man in the street, this means that both consist of electric particles. The only difference between them is the number of "wave-movements" per second executed by the "electric particles." 'Or as a technician would express it: the only difference between these two kinds of waves is in their frequency.
What this relation actually involves will become more impressive later, when we learn more about the electromagnetic wave-spectrum, and when we consider the fact that radio (or, as the scientists call them, Hertzian) waves go down to a wavelength of about 0.01-centimeter (4/1,000 of an inch).
Nobody, as yet, has been able to generate radio waves of such an extremely short wavelength (or, at least, not in considerable quantities), but there is no doubt that, in the future, someone will surprise us with the news that he has found a method to construct a transmitter which can generate these Ultra-Microwaves-as we shall call them, since there is as yet no official name given to them.
A very good indication that many scientists around the globe are paying attention to these very short waves lies in the fact that our daily papers have so often had rumors of that bugaboo of man - the so-called "Mystery Rays." According to these reports, this "secret brain-child" of science is undergoing intense research in one or another well-known laboratory; but the explanatory stories told by some papers are of quite frightful nature.
Inquiries at the laboratories, mentioned in these "baloney" articles, naturally provoke stern denials in each case. However, they do not change a bit the real situation, despite the fact that these sensational stories are written by reporters who do not know what it's all about. But, since the things they write about are mysteries to them, these pseudo-science-writers speak and write about "mystery" rays. Science, however, does not know and does not like "mysteries." Science knows only of known and unknown facts and, naturally, makes an effort to find out more about the latter.
The real story about these so-called "mystery rays" is the fact that the laboratories mentioned in the sensational articles are either occupied in learning more about the creation and application of very short radio waves, down to 0.01-centimeter or "cm." (see Fig. 1); or they are investigating the wave-range between 0.01-cm. (Hertzian waves) and 0.00008-cm. (red or low-frequency end of the spectrum of visible light rays) of which little is so far known. (The dimension 0.00008-cm. is, as Fig. 2 shows, a tiny part of an inch, or exactly 1/31,777-in.)
Despite the fact that 1/31,777-in. is not much to talk about, let's take a chance, and look into the wave-range, even below 0.00008-cm. At first it may seem unbelievable to some readers; but all of us are very well acquainted with this wave-range, and what's more, we know it very well down to 0.00004-cm. wavelength! But this is not all. Each of us is endowed at birth with means to receive these tremendously tiny ultra-ultra-microwaves!! The story of this means is not without a tragical note, for, if friends of ours have trouble with their "receiver" we say: "What a pity, he (or she) is blind." Or in case distortion occurs in their "reception," we call them "near-sighted," or "far-sighted," color-blind, etc. One does not need to be a scientist to know that this wave-range between 0.00008- and 0.00004-cm. is the one of visible light, as represented in Fig. 1; note, however, that the frequency limits used in this illustration are not at all arbitrary ones, in fact, may even overlap.
Governments Are Backing Research
Our discussion has shown us, so far, that we know approximately what to expect in the wave-range of the shortest of the radio waves, down to 0.01-cm. We all are quite familiar with the very much shorter waves of the visible spectrum, as we have seen. But we do not know very much about that portion of the wave spectrum between the shortest radio waves (0.01-cm.) and the visible light waves.
As we mentioned before, science does not know much about this space or gap - at least, not from the point of radio communication - but there is plenty of research going on in various parts of the globe to find out more about it.
And, what is, perhaps, most interesting is the fact that many of these laboratories are owned by governments which are pleased to give scientists "with promising ideas" a room in their research institutes (of course, a room with hermetically closed doors). The reasons for this great interest are the armies and navies which hope to find in this unknown realm of the wave spectrum something which will make a future war more terrible and creepy.
The Fight About the "Black Gap"
So far European "science sponsors" have been heavily disappointed, because there seems to be nothing in this gap "full of darkness" which can be used to give war machines more power to destroy. The European scientists, too, had disappointments of their own. They followed their commercial instincts, instead of considering their scientific eminence, and, in the hope of someday finding something in this unknown part of the wave spectrum which could be sold eventually to munitions makers, etc., did not publish the results of their research.
In the meantime, American scientists, concerned in this "black gap" only for its scientific interest, have not only published all the facts they found, but also have blocked the way to the patent office for many of the European inventors and scientists by applying, themselves, for the patents in question!
This happened about a: year ago. Since then, European scientists have been very busy in their scientific publications "telling the world" they did everything long before America even thought of these things! But that's their own trouble. The interesting points in this fight for fame are, so far as we are concerned, the facts unveiled.
The Photocell - The Starting Point
As we mentioned before, light waves and radio waves are one and the same thing, but only different in the number of wave-movements executed per second, and their wavelengths. The elementary proof that this is true is found in the photoelectric cell. Experiments with these cells have indicated that an electron emission can be obtained by directing a light beam, as shown in Fig. 3, upon the photo-sensitive layer of a photocell.
The photoelectric cell is, therefore, (to speak in terms of radio technique) nothing but a converter, so to speak, somewhat akin to the mixer-oscillator stage of the usual superhet. Now, let us look a little closer into the similarities of these devices.
The (combined) mixer-and-oscillator stage of the usual superhet. converts an incoming signal of radio frequency (R.F.) into a signal of intermediate (lower) frequency (I.F.). The signal remains the same, but the "form of propagation" changes. About the same thing happens when we change from an express train into a slowly-moving local train. A somewhat similar action happens in a photoelectric cell. A light beam (i.e., an impulse of an extremely high frequency) is converted into a direct-current impulse (change of "speed," but signal characteristics remain the same).
This complex conversion happens because the thin chemical layer of a photoelectric cell acts not only as a converter, but also as the 2nd-detector, and all by means of a tiny bit of caesium oxide. By mixing this alkali with other chemicals it was possible to extend the sensitivity of the photocell far into the wave-range of the infra-red rays.
Later on someone found out that the photoelectric effect can also be obtained when the light beam is thrown, not in the "regular manner" (directly onto the front of the photo-cell, as in Fig. A) but also upon the opposite side (as shown in Fig. 4) if only the photo-sensitive layer is made thin enough to be translucent.
Another important step was taken following an idea, first conceived by Dr. Zworykin of RCA; namely, to shoot the electrons which were obtained from a photoelectric cell (with a translucent photo-sensitive layer) directly upon a fluorescent screen (see Fig. C). How such a fluorescent screen operates is well known from the cathode-ray tube, where an electron beam falling upon the fluorescent screen causes an effect which is referred to as a fluorescent: light. This design of Dr. Zworykin's may be called an impressive triumph of modern science over nature's secrets, because he made it possible to receive invisible "light" in the form of infra-red light and convert it into visible light. This invention, when applied in the realm of shipping and the navy, means that it is now possible to see through fog, because infra-red light is not so readily absorbed by fog.
A New Kind of Receiver
But this is not all that makes Dr. Zworykin's invention so important ; he has also opened a way by which the enormous number of frequencies in the famous "black-gap" can be used for communication, especially for television transmission.
To understand the full importance of the new device for future radio communication, let's look again at Dr. Zworykin's wonder-tube, and compare it with a radio receiver of usual design. This comparison will give us an idea, how complicated and clumsy our present radio receivers are in the final analysis.
We need coils and antennas to bring the signal of a transmitter to the control-grid of the first tube of our receiver. We require oscillator-mixer circuits to convert the RF, signal received into an I.F. signal. Then follow the 2nd-detector, the A.F. amplifier and, finally, the reproducer or "loudspeaker."
Remembering that "radio" waves, and visible or invisible "light" rays are one and the same thing, but different only in their frequency, let's see how Dr. Zworykin does the trick.
He needs no coils or tubes in the "input stage"; referring to Fig. B. only an extremely thin layer of a photo-sensitive chemical to receive the signal. This layer not only converts the incoming light signal into an impulse of another frequency, but also rectifies the signal into a direct current (D,C.) impulse, in the form of an electron emission. A second thin layer, made of a fluorescent material, is then used to reverse the conversion process.
However, while the first layer converts a signal downwards in frequency (transforms light impulse of high frequency into D,C. impulses of, theoretically, very low frequency), the second layer of fluorescent characteristic converts a signal of a low frequency (D.C. impulses) into a high frequency. Or, in other words, it converts the D.C, electron beam into visible light, which is a signal of very high frequency.
ToToday we are able to receive and to transmit signals in the range starting with the infra-red light and ending with the range of the ultra-violet light. Tomorrow. someone, somewhere, will find a new photo-sensitive chemical, or a new alloy (in the form of a combination photoelectric cell and thermo-element) which will do equivalent tricks in those parts of the wave spectrum which are as yet unconquered; namely the remaining spot between the outskirts of the .infra-red rays and the shortest of the short radio waves.
As mentioned before, all the scientists working in this part of the spectrum have not yet announced their findings, but there are already certain indications which, when assembled in the proper order, give us an inkling into the future modes of radio communication, and the future trends of radio design.
Complicated receivers of today will shrink to a tiny glass ball, consisting in principle of two chemical layers, or even (and this is also of great interest) of 2 crystals. p>
A tiny "electron multiplier" arrangement, as it has been described by Dr. Zworykin and Philo T. Farnsworth, will amplify the signals received by the first layer (or by the first crystal) employed. In case optical reception is desired, a fluorescent screen will transform the amplified electron beam into light impulses. In case musical reproduction is desired, a second crystal, employed as sound reproducer, will probably do the trick. The principal design of such a future radio receiver is shown in Fig. C. Experienced readers will say: "It must be quite simple to build such a receiver after Dr. Zworykin did something similar with light rays, and since the Rochelle-salt crystal-loudspeaker is ready today as standard equipment." However, it only looks that way. There are quite a number of physical problems unsolved; but there is firm hope that these will be mastered in time to come.
Upon consideration of the enormous number of wavelengths, available in the range of the Ultra-Ultra-Microwaves, everyone can picture himself in possession of his own receiver and his own wavelength allotted to him, in a manner similar to the way in which we acquire today license numbers for our cars. To make this true, another problem must first be conquered: "How shall we tune these receivers to receive desired programs?"
HoHowever. a solution already exists for this problem, Let's look how photographers interested in color-photography "tune" their cameras to "catch" only the image of certain colors of the object to be recorded. They place filters in front of the lens system. Colors (or to speak in the language of radio technicians-"frequencies") not desired by the photographers are "tuned-out" (filtered) by means of a piece of stained glass and, since we also have to deal with waves-of this frequency-band, similar tuning methods will probably be applied.
Finally there is another difficulty to expect. That is the "quasi-optical" nature of these tiny ultra-ultra-microwaves. Since their frequency approaches that of visible light, their range will be restricted, approximately, to a distance corresponding to the optical range of vision. Antennas of odd form will be required to enjoy programs, transmitted on these wavelengths, in the apartments of our great cities.
A forecast of such an antenna is shown in Fig. A. As this illustration indicates, a reflecting mirror, approximately horn shaped, is fastened at the top of a high post. This form of reflecting mirror is necessary to receive signals from all directions. And, below this mirror we see a funnel-shaped or concave device. This funnel contains a large number of tiny "ultra-ultra-microwave receivers" or receiver cells - much as the eye of a fly is constructed with innumerable facets, each of which is an "eye" in itself. They will probably be arranged in circles, Each circle, containing a great many of these receivers, is "tuned" by means of suitable filters to a certain frequency; and the amplified electron-emission will be sent via multiple-wire cable down to the selector mechanism or control unit and the sound reproducer in the apartment. Eventually the "tuning" (Le., the movement of the filters( will be executed by remote-control devices from downstairs. p>
This all sounds quite expensive. But we should not forget the numerous and complicated parts contained in our present-day receivers, yet how much do we pay for a complete se? Or, for example: in the beginning of radio, we paid about $50,00 for a radio tube of quite simple design. What is the present price for a complicated metal tube? All these price problems are questions concerning only the competing manufacturers. Our interest is to include amateurs to think along the lines of the article.
Posted December 4, 2015