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
Light waves slowed down by the convex glass lens and radio waves
speeded up in the con-cave metal lens are bent in the same manner.
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.
This large metal lens concentrates radio waves more sharply than
can any other director.
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.
The portable Snooperscope and power supply. A modified form of
the instrument, called a, Sniperscope, attaches directly to a carbine.
The figures coming out of the dugout are quite invisible unaided
Electronic night sight reduced the infiltration menace in the
Pacific war theatre, it was revealed last month by R. H. Frye of the Electronic
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
"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