Radio Broadcast (Nov 1926-Apr 1927)

!ome Experiments on One Meter FIG. A special method, perhaps used for the first time by Mr. Hallberg, several years ago, for measuring short wavelengths with a single wire. Two points on the Lecher wire are found where a maximum deflection on the indicating meter is obtained. The distance between these two points is equal to half of the wavelength. The microphone is on the table near the transmitter. The antenna on the transmitter is evident, projecting upward at the right of the picture of the of a T; one (Mi of J. H, Used for g on One on the 300 of length— Plenty of Scope for Experiment Is Offered the Interested Amateur A CONSIDERABLE amount of work has been done during the last one or two years on short waves, between one and five meters (300,000 and 60,000 kc), and the special purpose of this article is to report on some work of this nature which has been done by Mr. J. H. Hallberg, and which should form a worth while addition to the information available at present. Mr. Hallberg has experimented with short-wave telephony for the last few years, having originally become interested in it through research work which he has done, relative to the measurement of very short wavelengths, and which made necessary the development and calibration of § to 10-meter oscillators and detectors. Most of the work done by other experimenters on ultra short waves was with pure un-modulated c. w., so that these experiments with modulation throw some light on the possibility of using telephony on very short wavelengths. Many experiments of the nature described here can be easily duplicated by readers of this magazine. It is necessary for those who experiment along these lines to possess an amateur station and operators' license, information on which can be secured from U. S. Radio Inspectors. Those who have concerned themselves with shortwave work, will find sufficient material about their laboratories to make the transmitter and receiver described in this article. It is the cheap MR. J. H. HALLBERG Whose interesting experiments with 1 -meter radiophony are described in this article ness and ease with which these short-wave experiments can be done that counts in part for the interest which they should create. The transmission experiments outlined here, were made on the sixth floor of a twelvestory steel apartment house, not the best place, by any means, to experiment on wavelengths between 1 and 5 meters. Steel girders, conduits, pipes, fixtures, metal grill work, etc., absorbed the greater part of the power, which, for most of the tests, was only about four watts. With this low power and with so many objects capable of absorption located in the vicinity of the transmitter, it was to be expected that the range would not be very great. With a single-tube receiver (no audio amplification) the voice, music, or the tick of a clock placed close to the microphone on the transmitter, could be heard about one-half mile away. This is not at all bad when it is realized that the per cent, modulation must have been quite low. Beyond about a half a mile the modulation could be heard but was quite weak. If the detector was made to oscillate, signals were increased in strength considerably but at the same time there was much distortion. Sometimes it would be found that the signals could not be heard in one location but that moving the receiver a few feet away would bring them in with good strength. Very likely the signals could have been heard further than half a mile away in certain locations with