Radio age (May 1922-Dec 1923)

RADIO AGE— "THE MAGAZINE OF THE HOUR" Design of a Portable Short -Wave Radio Wavemeter By U. S. Bureau of Standards A WAVEMETER is a device for measuring the frequency or the length of radio waves. Radio waves always travel with the same velocity, and if the frequency is known, the wave length is also known. Resonance is a most fundamental phenomenon of radio. When the inductance and capacity of a circuit on which an alternating electromotive force is impressed are adjusted so that the impedance of the circuit is a minimum and the current flowing in the circuit is a maximum, the circuit is said to be in resonance. For information regarding resonance and the measurement of wave length, reference may be made to "The Principles Underlying Radio Communication," Signal Corps Radio Communication Pamphlet No. 40, and to Bureau of Standards Circular No. 74. These publications may be purchased from the Superintendent of Documents, Government Printing Office, Washington, D. C. The price of the former is $1.00, and the price of the latter is 60 cents. Amateur radio stations in the United States are at present required by law when transmitting to use wave lengths not exceeding 200 meters, and it is therefore important that amateur operators should have a wavemeter available so that they may adjust their transmitting sets to comply with the law, and it is necessary that this wavemeter should be adapted to measure short wave lengths such as 200 meters. Other comparatively short wave lengths such as 360 and 485 meters, are now used for radio telephone broadcasting, and it is important to have a wavemeter which can measure these wave lengths. The Radio Telephony Conference which met in Washington in February, 1923, recommended narrow bands of waves for particular services, some bands being only 10 meters wide. Stations which must work within such narrow bands must be provided with welldesigned wavemeters if they are to comply with the requirements of the law. The design of a portable short-wave wavemeter is therefore a matter of importance. It is the purpose of this circular to point out the most important considerations in the design of such a wavemeter, and to describe the (Continued on page 25) Operating radio receiving set inside steel car on speeding Pennsylvania train. Receives in Speeding All-Steel Car PIERCING the all-steel construction of a railway passenger car on the Broadway Limited, the Pennsylvania Railroad's crack flyer, radio signals were successfully received on October 13 by a set entirely within the car, without outside antennae, while the train was speeding between New York and Chicago. A few strands of wire around an eighteen-inch frame attached to the set served as the receiving apparatus by which music and speech were caught from half a dozen stations en route. The tests, the first to be made on a moving train without an outside aerial, were conducted by Arno Zillger, chief engineer for the E-D Manufacturing Company, of Philadelphia, enroute to the Radio Show in Chicago. Mr. Zillger used an ordinary receiving set without any extra attachments or special parts, setting up the apparatus in 17 minutes as the train was about to leave Philadelphia and immediately tuning in to catch broadcasting from John Wanamaker's in Philadelphia. Even the 11,000 volt electric wires over the railroad tracks, where the Pennsylvania is electrified to Philadelphia suburbs, did not interfere with the receiving. Continuing the test through the evening, Mr. Zillger listened to messages and concerts from Newark, Schenectady, an ore boat on Lake Erie, Pittsburgh and numerous other points. J. D. Jones, superinterdent of Telegraph and Signals for the Eastern Region of the Pennsylvania Railroad, was one of the most interested observers of the experiments. The possibility of the use of radio in giving and receiving train orders is at present a subject of investigations on several roads and the results of Mr. Zillger's tests threw considerable light on the problem. Since the initial tests, Mr. Zillger has designed a new set especially for use on moving trains. This set will be given a try-out soon. The practicability of radio for use in communicating between the engine and the caboose of long freight trains, and between trains and stations along the line, is one of the angles which Pennsylvania railroad officials are watching closely. The results of last week's experiments, Mr. Zillger said, show that the idea is workable and that his set, with a few modifications, would prove successful in such work.