Your RF Cafe
March 1955 Popular Electronics[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Popular Electronics was published from October 1954 through April 1985. All copyrights are hereby acknowledged. See all articles from Popular Electronics.articles from Popular Electronics.
Just as early cellphones
(Motorola's Bag Phone, e.g.) required large
carrying cases to contain both the large electronics and the large battery required to operate the phone, some of
the first commercially available portable personal radio sets came with shoulder straps. Those that didn't have
straps had wheels and a handle. The "walkie-talkie" (originally called "handi-talkies")
designs were first seen during World War II
and then in Korea. In fact, this 1955 article
from Popular Electronics was printed shortly after the end of the conflict in 1953. Don't confuse the radio-based
portable field telephones with the ones
that had a pair of wires (sometimes thousands of feet of it) that did not need complicated circuitry for over-the-air
transmitting and receiving.
By Leo G. Sands
Bendix's MRT-9 portable two-way radio unit for the 152-174 mc. band.
The Bendix MRT-9 packset in its shoulder-strap protective case.
Motorola packset with a monitoring speaker on top of case.
The Motorola "Handie-Talkie" for 152-174 mc. band. Case is available to protect set from weather.
Vibrator power supply section of Motorola "Handie-Talkie." Note the non-spillable storage batteries in unit.
Two-way radio has captured the imagination of the public - here is the story on available units and operating rules.
The portable two-way radio has been brought vividly to the attention of the public by "Dick Tracy." His is the two-way radio which would sell like the proverbial hot cakes if it really existed. Many are trying to develop a "Dick Tracy" radio and no doubt someone will succeed.
Today, crime fighters must content themselves with somewhat heavier and bulkier portable two-way radio sets. Several excellent portable units are on the market and they do a commendable job, even if they fall short of the performance of "Dick Tracy's" wrist radio.
Depending, upon their size and form factor, they have been called, among other things, a walkie-talkie, "Handie-Talkie" (a trade name), pack set, "Port-A-Fone" (also a trade name), and a breakie-backie.
If you buy a pair of walkie-talkies, there is no assurance you can use them. All radio transmitters, even flea-powered, hand-carried portables, must be licensed by the Federal Communications Commission (FCC). Different kinds of walkie-talkies are designed for licensed operation in different categories of radio services as defined by the FCC. Equipment for use in the industrial, land transportation, and public safety radio services must generally meet more rigid technical standards than equipment to be used in the Citizens or amateur radio services.
Unless you operate a business which is eligible for licensing in the land transportation or industrial radio services or unless you are an amateur radio operator, you as an individual can only operate walkie-talkies in the Citizens radio band. The Citizens band is open to all citizens whether for private personal use or in connection with a legal commercial enterprise.
For use only in the Citizens radio service on 465 megacycles are such low-priced, hand-carried two-way radio units as the Stewart-Warner "Port-A-Fone." Here, the range is limited from a few hundred feet to a mile or more, depending upon local conditions. This type of unit uses a super-regenerative receiver which is converted into a self-excited AM transmitter.
The more widely used and more expensive portable two-way radio units are designed for operation in either the 25 to 50 megacycle or 152 to 174 megacycle v.h.f. (very-high-frequency) bands which are reserved exclusively for eligible commercial enterprises and government agencies.
To meet FCC requirements, these commercial pack sets employ crystal-controlled transmitters operable on one or two specifically assigned fixed frequencies within the band for which the equipment was designed. Fixed tuned superheterodyne receivers, which are also crystal controlled, are used. Transmitter and receiver are packaged in the same enclosure along with either wet or dry batteries.
(Left) RCA's lightweight walkie-talkie for the 25-50 mc. band. It uses a Western Electric type 500 handset. (Right) Interior view of typical unit using miniature and subminiature tubes.
Both subminiature and miniature type tubes are used in commercially available walkie-talkies. The transistorized walkie-talkie has not yet made its debut and is not expected to do so, at competitive prices at least, for quite some time.
The antenna used with nearly all of the commercially available walkie-talkies is either a vertical flexible quarter-wave whip or a telescoping antenna similar to those used in automobiles. An external antenna may be used in fixed or mobile applications by removing the antenna and plugging in a coaxial cable leading to the antenna.
The range obtainable with walkie-talkies is sometimes amazing, especially when operating in the 25 to 50 megacycle band. A range of 8 or 10 miles between a walkie-talkie and a higher powered base station is often reported. However, much depends upon terrain conditions.
Pack sets are used by many railroads to extend communications to the man on foot. The unit shown here is manufactured by Hallicrafters.
The range between a pair of walkie-talkies is generally quite limited because of the power output of the transmitters and because of the low effective antenna elevation. Of course, the range can be several miles if one walkie-talkie is operated on a hill top and the other one is within line-of-sight or at a point where signals are easily reflected.
In railroad yards, for example, many have been disappointed to find the range attainable between a pair of pack sets is so short as to be unsatisfactory. This is particularly true when one or both walkie-talkies are carried by personnel standing or walking between freight cars. This would also apply in congested areas as in city streets lined by tall buildings or many trees.
The cure in such cases is to employ a relay station if permitted by FCC regulations in the service in which the equipment is to be operated. When using a relay station, two different radio frequencies are required, one for transmitting and one for receiving.
Motorola and General Railway Signal Company have developed novel portable transmitters for one-way radio communication. They are not much larger than a flashlight and are primarily used in railroad yards where personnel on foot talk out over a portable transmitter and receive calls and replies over a public address system. A typical walkie-talkie like the MRT-8 manufactured by Bendix weighs only eight pounds and is available for hand carrying or for mounting on personnel with suitable straps. Hallicrafters manufactures portable two-way radio units which can be adapted for installation in motor vehicles. Power is derived from the vehicle's electrical system.
Three versions of the Hallicrafters "Littlefone." (Left) The standard model with handset. (Center) Unit adapted for under-the-dash mounting in a car. It is powered by car battery. (Right) "Littlefone" with a 4" speaker mounted on case.
In the land transportation, industrial, and public safety radio services, persons using mobile and portable stations do not need operator's licenses although the operator of an associated base station must possess a restricted radio telephone operator's permit. Although a station license is required for Citizens band walkie-talkies, an operator's license is not needed.
It is possible to build your own walkie-talkies for use in the Citizens band or in one of the commercial radio services. However, to build such equipment so that it will comply with FCC regulations requires considerable skill, a vast amount of precision test equipment, a good deal of time, and ample funds. It is generally cheaper to buy factory-made equipment. Commercially available walkie-talkies cost from $200 to $500 each.
Posted February 17, 2014