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Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024

Webmaster:

    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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Radio Electronics Monthly Review
August 1945 Radio & Television News Article

August 1945 Radio-Craft

August 1945 Radio Craft Cover - RF Cafe[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.

Although not specifically stated, some of the technology reported in this August 1945 issue of Radio-Craft magazine was not so long before classified technology developed during World War II. The Radiotype system of wireless teletype developed by General Electric was an early attempt to provide a mobile means of sending and receiving hard copy messages. It was a rather complex scheme that used a typewriter to drive a tape punching apparatus, which was fed into a radio transmitter to send coded tones (as opposed to CW pulses) for a receiver to then decipher and drive an Electromatic typewriter. The demonstration used a police car to carry remote equipment. In related news, RCA's wireless 488 word-per-minute (wpm) telegraph multiplexer using time division multiplexing (TDM)  Also featured was the FCC's decision to move the commercial broadcast FM band from 54-88 MHz up to 88-106 MHz (now up to 108 MHz, but then the upper 2 MHz was reserved for teletype). Technology was on the move.

Items Interesting to the Technician

Tone signals and Radiotype apparatus as a means of combatting crime were demonstrated at the recent visit of the New York State chapter of the Associated Police Communications Officers to Schenectady, G-E reported last month.

The Radiotype equipment uses a standard Electromatic typewriter applied to communications apparatus. In full automatic operation, copy is typed on a sending typewriter which perforates a tape. This tape is "read" by an automatic transmitting head which keys the electronic communications unit, sending out a tone signal. This tone signal is sent over a radio circuit, the same as a voice signal. At the receiving end the tone is fed into an electronic unit which selects the proper keys on the receiving typewriter which prints the message. The G-E boys caught the tones on a magnetic recorder, later running the wire off again to actuate the receiving apparatus which typed out the message. Transmission by Radiotype over regular F11 circuits was also demonstrated to the visiting police communications men. At the Helderberg mountain site of G.E., 50 police officers were shown a one-way demonstration of Radiotype when messages were sent from the company's plant, about 0.13 miles away. This operated on 35.46 megacycles. The engineers had voice communication between the mountain and plant by standard FM emergency equipment and used the same equipment to transmit the Radio type.

Equipment used in the Radiotype G-E demonstrations - RF Cafe

Equipment used in the G-E demonstrations.

Making Radiotype tapes - RF Cafe

Making Radiotype tapes.

While no attempt was made to multiplex voice and Radiotype over the same carrier in this demonstration, the engineers explained that this has already been done without interference on either channel.

Voice communication was also demonstrated on a frequency of 161.775 megacycles using experimental mobile FM equipment. (FM voice communication by police radio systems have heretofore been in operation on frequencies between 30-40 megacycles and between 116-119 megacycles.) This new frequency (161.775 megacycles) is in that part of the radio spectrum which the Federal Communications Commission has proposed for new emergency communication uses by police and fire departments.

A car was equipped with 4-watt experimental FM radio apparatus which enabled the engineers in the car to talk from various parts of the Capital District to engineers and their guests at the G.E. transmitter site in the Helderberg Mountains, The car transmitter was heard at various distances up to 50 miles away. The channel from the Helderbergs to the car was conventional 30-40 megacycles equipment; the talk-back was on 161.775 megacycles.

Maintenance of present radio receivers will take precedence over production of new sets in the allotment of new radio tubes, the War Production Board stated last month. When new tubes are made in quantity, strict priority will be given to repairmen for the purpose of keeping existing radios in service, over manufacturers who would use them in new receivers.

WPB officials suggested that authorization of 4,000,000 civilian radio tubes per month. might soon be forthcoming, but were silent as to just how soon that might be.

Army spokesmen reported that cancellations of military tube orders were being made in small numbers, and stated that the Army's present stockpile was now being re-examined and might possibly reveal stocks which would make further cancellations possible.

According to WPB estimates, it will take an average of 1 1/2 tubes per set to put the "silent 9%" of America's receivers back into action. Thus the first million tubes would restore 660,000 sets, where the same number would spread over only 200,000 five-tube, and a smaller number of larger new receivers.

FM Allocations were fixed between 88 and 106 megacycles by the Federal Communications Commission on June 27. Twenty of these channels, between 88 and 92 megacycles, are reserved for non-commercial educational FM stations.

Six channels are assigned to television, one between 44 and 50 megacycles, three between 54 and 72 and two between 76 and 88. Amateurs will occupy the frequencies between 50 and 54 megacycles allotted to them by the Commission early in the year. This will continue the old "5-meter band" which formerly ran from 56 to 60 megacycles.

The remaining space in the spectrum between 44 and 108 megacycles was allotted as follows: facsimile, 106-108; non-Government fixed and mobile services, 42-44 and 72-76 megacycles. This closes the allocation of frequencies between 25 to 30,000 megacycles.

The FCC believes the present decision, moving FM "upstairs" from the band between 42 and 50 megacycles, will make it freer from interference and other shortcomings than it would be in any other portion of the spectrum.

Recognizing that considerable opposition was advanced by manufacturers and engineers skeptical as to the advantages of the higher-frequency band, the Commission stated that it "has a duty to consider the long-range effects of its action as well as the effects during the months immediately ahead, and it doesn't propose to provide an inferior FM service during the decades to come merely because of the transitory advantages which may be urged for an inferior type of service."

Television will appear as an executive force in the postwar world, holding large companies together and permitting a closer-knit management than is now possible, reported International Business Machines last month, announcing its intention of providing television relay facilities on a common carrier basis for business use.

With the help of television, a chain store with branches in all parts of the country could maintain a daily or hourly checkup on receipts, inventories, sales, etc. All the bookkeeping could be handled in a central office. Such organizations as railroads, with their widely-scattered equipment and centralized organization, would also benefit greatly by the use of television.

Dealers interviewed by McCall's Magazine expressed opinions differing in many instances from those of the nation's customers, according to a survey whose results were announced last month.

Better radio furniture for the postwar radio is the first requisite for sales, according to the 376 dealers interviewed. The three most popular models will be the table radio, the console combination and the table combination, not necessarily in that order. Dealers saw no future for the console radio without phonograph, and suggested that manufacturers would be well-advised to discontinue the model.

Among console radios, the type in which the record player pulls out was the favorite, with 253 votes out of 329, the remainder of the 376 dealers not voting. The "lift top" was next, with only 40 votes, while the tilting front type and the combination in which the top must be lifted to get at either radio or phonograph split only 36 votes between them.

The question of brand loyalty raised in consumer surveys also appeared among dealers. While the majority stated that they expected to carry the same brand as pre-war, most of them had reservations. It was pointed out that in radio, far more than in other electrical appliances, new names had a habit of springing up and dominating the market for a few years, before giving way to another or fading out entirely.

On only one thing the dealers were in agreement - the assured future of FM.

Multiplex distributor used by RCA to send over 8 channels simultaneously - RF Cafe

The multiplex distributor used by RCA to send over eight channels simultaneously.

Multiplex telegraphy, long familiar on wire circuits, will now speed up transmission by radio while cutting errors to the zero level, according to a report released last month by the Radio Corporation of America.

By means of specially designed equipment which employs what is known in the industry as "time division multiplex telegraph" principles, the equipment can handle 488 words per minute inward and outward simultaneously, corresponding to eight channels each way with an individual channel speed of 61 words per minute. The equipment also permits operation of four or two channels instead of eight" channels, when desired.

All eight channels may be utilized for two-way communication with one distant station. Alternatively, they may be set up in such a way that four channels with a total capacity of 244 words per minute can be operated in both directions simultaneously between two different stations, with automatic retransmission of one or more of the channels to a third station.

Moreover, printing mechanism incorporated in the system accomplishes the feat of making the circuit virtually error-proof, despite its high speed. Let any letter be mutilated or garbled in transmission and a warning bell rings under the receiving printer. At the same instant, in lieu of the mutilated character, a maltese cross appears to mark the exact spot of the error and facilitate correction. In other words, no error can get through directly to the message blank.

Another bell, of noticeably different pitch, is operated by means of a switch similar to a telephone dial. With it the receiving operator can pass a number of stock phrases for service instruction to the other end of the circuit, thereby saving channel operating time.

The multiplex distributor used by RCA to transmit over eight channels simultaneously.

The printer is completely automatic and, in conjunction with the multiplex mechanism, the system functions with a minimum of circuit time. Each incoming letter is comprised of three marking (signal) impulses, plus four spacing (no signal) impulses. The name - seven unit - stems from this fact. Automatic counting features incorporated in the receiving printer check the arriving impulses, and if the marking impulses vary from three, the warning bell sounds and the maltese cross emerges to report an error.

Vital to the system is a newly perfected method for keeping the receiving channelling devices in exact step with the distant transmitter and the signal elements being sent through the air.

Improvement in time division multiplex operation has been achieved through the inclusion in the same mechanism of the devices that perform the basic channeling function and also of the face plates which pass the signal elements from or to the seven-unit printing equipment in the proper sequence and at the right time intervals for transmission and reception.

In physical appearance, transmitting and receiving equipment used in the new RCA system is at but slight variance from conventional radiotelegraph apparatus, in spite of its amazing performance. At each terminal of the circuit are two cabinet racks 84 inches in height, each containing a multiplex distributor, visible about half-way between top and bottom. One rack is primarily for receiving and the other primarily for transmission. Other equipment includes printers, keyboard perforators and tape transmitters.

The amazing performance of the new circuit leads the engineers to predict wide use for eight-channel equipment in handling postwar traffic.

 

 

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