Radio-Electronics Monthly Review
June 1946 Radio-Craft

June 1946 Radio-Craft [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

A month prior to this Metal Lens news item appearing in Radio-Craft magazine (May 1946), the inventor, Bell Telephone Laboratories, ran a full-page advertisement boasting of their accomplishment. As mentioned in my write-up, it is sort of akin to the Osgood optical lens used in lighthouses. Imagine performing the mathematical calculations required to design that thing using a slide rule! Also reported here was the resumption of regular television broadcasting in England by the BBC after war-caused alterations in programming. Compared to the capability, compactness, and weight of modern night vision equipment available today (see examples on Amazon for <$200), the "Snooperscope" presented here is a very crude device. It relies on a powerful infrared light source emanating from the scope to reflect off the target and cause a luminescent lens to glow in order to generate an image. A journey of a thousand miles begins with the first step, as the saying goes.

Mag Tag: Electronic Night Sight (a la IR LEDs on Web)

Radio-Electronics Monthly Review

A Metal Lens which focuses radio waves as a glass lens focuses light is expected to fill an important role in microwave relay systems. Similar units, developed secretly for military use, distinguished themselves in comparison with older types of radio wave directors.

The new lens was designed and developed by Dr. Winston E. Kock and his associates of Bell Telephone Laboratories' technical staff.

It operates on a principle roughly akin to that of a simple convex magnifying glass. The action of the glass is to delay the advancing wavefront by an amount that is greatest at the center of the lens, where the glass is thickest, and least at the tapered periphery. As a result, the wavefront is reformed and headed so as to converge toward a point. This change in the velocity of a wavefront is a fundamental principle of all lenses.

Since radio waves are of the same electromagnetic nature as light waves, it has been known theoretically for some time that radio lenses on this principle might be built. Previous to the advent of microwaves, there was an insuperable obstacle in the very much greater length of radio waves, which in the commercial broadcasting band range from an eighth to a third of a mile. For a lens to be effective, it should have a diameter of at least several times the wavelength. This would have meant a lens almost a mile wide.

It was in pondering this problem that Dr. Kock thought back to waveguides, those hollow tubes which one of his colleagues had devised some years earlier to conduct microwaves and which, in war, were to play so vital a role in supplying a physical channel for radar signals.

It was known that radio waves under-go a speeding up, or increase in wavefront velocity, when they pass along such a tube or between metal plates and that the total advance of the wave-front could be fixed by controlling the length and contour of the plates and the distance between them.

It occurred to Dr. Kock that an array of metal plates could be designed to focus radio waves just as effectively as a solid lens might focus them if due regard were given to the fact that the edges of the wavefront would be advanced rather than retarded in transit. Such a structure would also be easier to build, move and maintain than an equivalent solid lens type.

The necessary design theory was worked out in mathematical detail and systems of metal plates were subsequently built to duplicate the action not only of convex and concave lens but also of other optical devices, such as half and quarter wave plates and prisms.

The drawings compare an electronic lens with an optical one. Because the waves handled are an appreciable fraction of the diameter of the lens, some things can be done with them that can-not be paralleled with their glass counterparts. The concave lens elements, which consist of metal sheets, instead of becoming progressively wider toward the lens edges, as shown in the drawing, can be cut back every half-wavelength or multiple thereof, thus saving metal and making a lighter structure. The back of each metal plate thus resembles a huge saw, one side of each "tooth" following the lens curve, the other side straight and parallel with the lens axis.

British Television will resume war-caused interruption of almost seven years on the seventh of June at 3:00 pm, a British Broadcasting Co. notice announced last month.

Pre-war practices, including the 405-line standard will be used. Thus pre-war receivers can be put into action With no modification, the report stated.

"Spy Radios" picked up at various points in occupied Italy, were revealed last month to be ordinary radiosondes, released by American meteorological services and plainly marked as U. S. Government property.

A pint-size spy scare had been aroused before the true nature of the mysterious instruments was revealed, and at least two European powers were accused by opposing factions of undercover intervention in Italian politics.

The scare reached even to the United States, and reputable American papers pointed out solemnly that the transmitters were of the "tiny type suitable for agents inside enemy lines." The label "Notice to finder; this instrument belongs to the United States Government," according to the same source, "signified only that it is pretty certainly not Americans who are dropping the radios, as there could be no conceivable reason for the Americans or British to use that method to distribute any radio apparatus they wished to distribute in Italy."

From the description, the radios were very standard radiosonde apparatus, and apparently could not have been turned over to technical personnel for inspection, as the barometer and hygrometer, contained in each, as well as the highly special switching system, would have identified them immediately.

Electronic night sight reduced the infiltration menace in the Pacific war theatre, it was revealed last month by R. H. Frye of the Electronic Laboratories, Indianapolis.

The device (known as a "snooper-scope") looks like an ordinary short telescope such as may be seen in various sighting devices, with an additional disc-shaped object mounted just below it. The disc is in reality a very powerful infra-red lamp and lens, projecting a beam of invisible "black light."

The infra-red rays, reflected from objects in their path like ordinary light, operate the receiving end of the instrument. Though this looks like an ordinary telescope, it is more like a television tube. Only the lens at the front of -the tube is a real optical device. The reflected infra-red rays are picked up by this objective lens and focused on the image tube, causing a photo-sensitive screen to emit electrons in direct proportion to the intensity of the invisible rays.

These electrons proceed down the tube, accelerated by high-voltage electrodes, and strike an ordinary fluorescent screen at the other end, causing it to glow and thereby producing a visible image which reproduces faithfully the details of the original scene. Thus the rays pass through three stages - beams first of infra-red "light," then of electrons, and finally of visible light - before reaching the eye of the beholder.

All power for the apparatus is supplied by a storage battery, which, with the vibrator power pack which supplies high voltage for the image tube, is carried on the operator's back.

A soldier with a "sniperscope" (a "snooper scope" mounted on a carbine) was said to be more effective in stopping infiltration than 12 men with regular weapons. Here is how the infra-red carbine operates, as explained by an Electronic Laboratories official:

"A fighter armed with a sniperscope hears a sound. He points his weapon into the darkness, peers into the telescope, and turns on the power supply.

He moves the weapon back and forth, like an invisible searchlight, his eye, pressed to the telescope, until he sights the enemy, slowly crawling forward.

"The enemy soldier is unaware that he is impaled by a beam of invisible light of a greenish hue. (In the telescope all objects appear as various shades of green regardless of their color in daylight, due to the use of high-sensitivity green phosphor on the cathode-ray tube screen.) The U. S. soldier focuses his telescope quickly, lines up a bead on the enemy with the telescope sight, and, with a press of the trigger, there is one less infiltrating enemy."

Posted September 22, 2021