Radio-Electronics Monthly Review
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In the middle of the last century, progress in television and radio technology was the focus of public attention, similar to news of the latest advances in smartphones and Wi-Fi-connected gadgets are today. Then, it was the installation of microwave relay networks for long distance telephone and television interconnections as reported in this 1948 issue of Radio-Craft magazine. Now, media headlines tell of new 5G cellular network equipment and small cell stations being installed around the world. New portable pocket radios using a single low voltage "peanut" vacuum tube or a germanium transistor are today's iPhones, smartwatches, and IoT-connected appliances. The item that caught my attention was mention of General electric (GE) issuing warnings that radar-equipped cargo airplanes should not be used to transport photo-flash camera bulbs because experiments showed exposure to certain frequencies and power levels of microwave power could set them off. A 1955 story in Popular Electronics had a photo of fluorescent light bulbs being energized by radar beams. Radar pioneer Sir Edward Appleton's 1947 Nobel Prize in Physics award is covered as well, along with a few other interesting items. Radio-Electronics Monthly Review Television Programs and telephone conversations are now being beamed from New York to Boston via microwave. The experimental radio relay system was formally opened by the Bell System on November 11.
Programs are relayed south of New York by coaxial cable and north by the microwave relay system. The two terminal points of the radio relay system are the headquarters building of the American Telephone and Telegraph Company's Long Lines Department at 32 Avenue of the Americas in New York and the Bowdoin Square building of the New England Telephone and Telegraph Company at Boston. Between terminal points, the microwave beam makes 8 jumps via 7 intermediate radio relay stations spaced about thirty miles apart. To secure the unobstructed view between antennas necessary in microwave transmission, the stations are built on hilltops: Jackie Jones Mountain, 5 miles west of Haverstraw, N. Y.; Birch Hill, about 3 miles south of Pawling, N. Y.; Spindle Hill, 5 miles north of Waterbury, Conn.; John Tom Hill, at Glastonbury, Conn.; Bald Hill, 5 miles east of Stafford Springs, Conn.; Asnebumskit Mountain, 5 miles northwest of Worcester, Mass.; and Bear Hill at Waltham,. Mass. On the roof of each radio relay station are 4 antennas, 2 facing along the route toward New York, 2 facing along the route toward Boston. This allows for 2-way operation - with one antenna of each pair for transmitting, the other for receiving. The antennas are ten feet square and incorporate a metal lens capable of focusing the microwave signals into a sharp beam. The initial equipment comprises a regular and a spare circuit in each direction. For operation of these 2 circuits, frequencies in the range 3700 to 4200 megacycles have been assigned by the Federal Communications Commission. Each circuit carries a signal band width of about 5 megacycles. Terminal equipment capable of carrying 240 simultaneous telephone conversations will be installed for experiment next spring, and it is expected that more channels will be added later. Radar may set off photo flashbulbs carried in planes, General Electric officials warned last month. G-E factories have accordingly been instructed to ship no more flashbulbs by air. General Electric said recent experiments have established that the lamps, with the exception of the primer type, can be ignited by high-energy short-wave electromagnetic radiation such as is encountered from radar transmitters.
Sir Edward Appleton at one of his pieces of technical equipment.
First of the Citizens Radios is this little two-pound transceiver. John M. Chamberlain, Civil Aeronautics Board safety-bureau director, stated there was no indication as yet that small airborne radar sets, like those that must be installed by February 15 in all passenger planes, are likely to set off the bulbs. These sets are to be installed to give pilots information about terrain and to warn when planes come too close. Presumably even large ground radar transmitters would be effective only over a range of a few feet. Radar Pioneer Sir Edward Appleton has been awarded the 1947 Nobel Prize in Physics. His researches have been of great direct importance to communications as well as radar. A pioneer investigator of the ionosphere or "radio roof" surrounding the earth, Sir Edward proved by direct experiment the existence of the layer of ionized atoms 115 miles or so high, present both day and night, which reflects short radio waves at night. His later work with radio reflections led directly to radiolocation, as radar was originally called in England, and his work was one of the underlying factors of Britain's early radar preparedness which was so decisive in the early stages of the last war. The invisible reflecting layers of the ionosphere have been the subject of intensive research since their existence was proved. Today calculation of their height is important in determining the best frequencies to use for radio communication over great distances. Radar Navigation may be hampered by archaic laws under which a radar-equipped vessel involved in a collision may be held liable for damages, Vincent A. Catoggio, New York marine lawyer, warned last month. The inland and international navigation rules, which were adopted in 1897, provide that a vessel shall slow down to "moderate speed" in a fog. "Moderate speed" has been interpreted by the courts to mean a speed that will permit a vessel to stop "within the limits of visibility." Since one of the most important features of radar is that it permits greater speed in fog, this ruling would negate much of its value, unless courts would decide that the visibility of radar could be considered a substitute for the traditional "rule of sight." Citizens Radio will soon become an actuality with the help of printed circuits and new high-frequency tubes. A transceiver already tested and about to be put in production by Gross Electronics Co. operates on the 460-470 mc band. It was exhibited by its developer Al Gross, president of the company, at the recent printed-circuit symposium in Washington. The radios will be sold in pairs tuned to their own private frequency within the 460-470 megacycle range, the Citizens Radio Band, thus reducing eaves-dropping. Each set is a self-contained transmitter and receiver. They will sell at less than $200 a pair. Volume production eventually should bring the price down to about $100. Performance varies under different conditions. On ground level in the city, the equipment has operated satisfactorily for distances up to four miles. Tests made in various cities resulted in perfect reception over varied distances among city blocks. In a ground to plane test, it made good contact between Cleveland Airport and Sandusky, 60 miles away. The transmitter and receiver of the civilian walkie-talkie weighs 11 ounces with antenna, is 6 inches long by about 3 inches wide by 1 1/4 inch thick. With batteries and leather case, the overall weight of each set is little more than two pounds.
Posted December 11, 2019 |
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