Radio broadcast .. (1922-30)

The Grid QUESTIONS AND ANSWERS The Grid is a Question and Answer Department maintained especially for the radio amateurs. Full answers will be given wherever possible. In answering questions, those of a like nature will be grouped together and answered by one article. Every effort will be made to keep the answers simple and direct, yet fully self-explanatory. Questions should be addressed to Editor, "The Grid," Radio Broadcast, Garden City, N. Y. The letter containing the questions should have the full name and address of the writer and also his station call letter, if he has one. Names, however, will not be published. Some receiving sets are provided with dials, marked from o to 100 and others are marked from o to 180. How is it possible to determine the wavelength for a given setting of the dials? B. T. H. Los Angeles, Cal. THE marking on most receiving sets can not be used as a direct method of determining the wavelength of received signals and is provided so as you may have some definite idea of where to look for certain stations, after you have once been able to tune them in. After a station has been heard, you may make a record of the position of the dial or dials and it is quite likely that the same station may again be heard by making the same adjustment. There are some sets, which are used extensively, such as the Westinghouse and the Grebe, which are provided with dials which do not indicate wavelengths directly, but we have become accustomed to using them and know about where to find stations operating on given wavelengths. Provided the antenna is of the dimensions recommended, it is found that most broadcasting stations may be picked up by the Westinghouse "RC" receiver with the dial indicating approximately 30. The Grebe receivers of the variocoupler and twin variometer type are provided with a wavelength chart which indicates the wavelength for dial settings in the secondary circuit. By this method, stations of known wavelength may be picked up by setting the proper dial and then adjusting the others. The wavelength of any station within range of the set may be measured by first properly tuning the receiver and then reading the wavelength from the chart for the particular setting of the secondary tuning dial. In instances of this sort the wavelengths are not very accurate but serve quite well for all practical purposes, and where accurate measurements are required a wavemeter should be employed. What is the best crystal for a receiving set and bow far should it be possible to receive from a broadcasting station with a welldesigned crystal set? A. B. K. Galveston, Tex. FOR all around reception, it is doubtful that any crystal will give better results than may be had from galena. Merely procuring a piece of galena and putting it in your set, however, will not do. It is necessary to procure a large-sized piece and break it up into smaller pieces, testing each piece. It may be necessary for you to try a great many pieces before you find one which is truly sensitive, but the task is entirely worth while. A very good method of testing crystals is to have a double detector stand or two detectors which may be thrown into the same receiving circuit at will; one is used with any crystal and the other is used as the test stand by placing var ious crystals in it. As soon as one crystal is found which gives satisfactory results it may be used as the standard and others may be compared to it. In making the comparison, some single transmitting station should be picked out and the strength of its signals used as the determining factor. The crystal is the heart of the crystal receiving set and some of the sets which have been thrown back on the hands of their manufacturers by dissatisfied purchasers would have given satisfaction if a little more care had been exercised in selecting the crystals with which they were equipped. It comes more or less as a shock to most new radio enthusiasts to learn that the commercial operators on shipboard have received signals with crystal sets, without any amplification whatever, over distances in excess of eight thousand miles. One operator, in making a trip from New York to San Francisco by way of the Straits of Magellan, received press dispatches from the old Telefunken Station, located at Sayville, Long Island, nearly every night of his voyage. Another operator, on a trip from an East Coast port, through the Panama Canal, to Corral, Chile, which is some two hundred miles south of Valparaiso, received press, weather reports, and time signals from the U.S. Naval Station at Arlington over his entire trip with the exception of four days, and these four days were spent in the Torrid Zone where the static was extremely severe. No amplifiers were used and the results obtained are not at all uncommon. No such results as these may be expected from a broadcasting receiver, but you may be sure that the range over which your set will operate depends to a very great degree upon the sensitivity of the crystal you employ and the skill with which you are able to locate its most sensitive points, and this skill comes with continued use. How is the regeneration accomplished with the standard variocoupler and two-variometer book-up, when there is no inductive relationship between the placement of these three units? L. P. New York City YOUR question is quite like many others we have received, and the following explanation may be helpful, though it is truly a repetition of material already published in articles appearing in Radio Broadcast. To begin with, you are not quite correct in the assumption that there is no inductive relation between the elements for the primary and secondary of the variocoupler are in inductive relation to each other. The grid variometer is usually connected in series with the secondary of the variocoupler and thus becomes a part of the same circuit and, though it is not in direct inductive relation to the pri