Radio Broadcast (Nov. 1925-Apr 1926)

226 RADIO BROADCAST ADVERTISER BE SAFE — the Fire Underwriters Radio Code calls for the installation of a lightning arrester whereever an outside antenna is used. The Jewell Arrester — — has been approved by the Underwriters (see their Certificate No. E-5403) for both indoor and outdoor installations. It is mounted in an attractive brown porcelain case and is easily installed. Radio Instrumentsask your dealer for a Jewell 15-B Radio Catalog — or write to us. Jewell Electrical Instrument Company 1650 Walnut St., Chicago, III. Making Good Instruments for 26 Years THE GRID itig the Problems of our Readers QUERIES ANSWERED 1. WHAT IS THE PROPER METHOD FOR PLACEMENT OF COILS IN A TUNED RADIO-FREQUENCY amplifier? — F. H. J.— Houston, Texas. 2. WHAT ARE THE PRECAUTIONS THAT SHOULD BE OBSERVED IN ERECTING AN ANTENNA NEAR POWER LINES? C. A. C— Buffalo, New York. COIL PLACEMENT IN AN R. F. AMPLIFIER IN A receiver employing one or more stages of radio-frequency amplification, satisfactory results depend largely upon whether or not these amplifiers are properly neutralized. Now, neutralization depends upon several things. The internal capacity of the amplifier tube must be balanced; the wiring to the tube must be such that no coupling effects are obtained; and the Swivel ' with Set Screw FIG. I several radio-frequency transformers should be so placed and located that there is no electromagnetic coupling between them. It is this last point which we will discuss here. Most of us have had an opportunity to view the inside of a neutrodyne and to observe the peculiar angle at which the coil units are turned. At such a setting there is a minimum of coup 3. WILL YOU DESCRIBE A METHOD OF MEASURING THE RESISTANCE OF COIL UNITS TUNED TO PREARRANGED FREQUENCIES? — B. H. R. — Utica, New York. 4. WHEN I REPLACE THE 3-VOLT TUBES IN MY SET WITH 5-VOLT TUBES, THE SET OSCILLATES. WHY? T. M. B. — Boston, Massachusetts. right angle coupling between the coil units be employed. See Fig. 2. It is most important that, in the construction of a radio-frequency amplifier, or a receiver containing one or more stages of radio frequency amplification, the tube sockets be so placed that the grid leads are as short as possible. PRECAUTIONS IN ANTENNA ERECTION THE other day a serious accident occurred in Waltham, Massachusetts, caused by a young man drawing an antenna wire across an electric power line. The fact tha* the line was insulated did not matter as his antenna wire soon cut through the insulation, and thus the current was communicated to his body. The problem of antenna installation has caused carelessness on the part of a great many fans throughout the country, and it has been the cause of many fatalities. The following general "Don'is" relating to antenna erection are given in a paper by Mr. Clarence V. Purcell, of the Boston Edison Company, for the benefit of those who would profit by the example of others who have been unfortunate enough to become involved in some needless mishap: Don't run an antenna over or under any other wires carrying an electric current of any sort, 1st R.F. Tube 2ndR.F.Tube 2nd R.F. Coil Detector FIG. 2 ling between the coils. This placement can be approximated by the home experimenter in his own construction. Individual test must be made to determine the point at which satisfactory neutralization is obtained in the regular manner. As an aid in obtaining the desired results, it is suggested that in the construction of a receiver the coil units be only temporarily fastened to permit ready change and variation in the angle at which they are to be set. See Fig. 1. I fit is not possible to approximate this angle, which is about 55 degrees from the horizontal, or if there is plenty of space in which to construct the amplifier, then it is suggested that a if Tested and approved by Radio Broadcast -fa whether these wires be high tension wires, service wires, or telephone lines. Don't attach an antenna to any pole or tower to which other wires are attached, or climb or attempt to climb such poles or towers for any purpose. Don't run an antenna over or across any public highway. Don't attach an antenna to any electric light, telephone or telegraph pole, even though no other wires are attached thereto. If using an outside antenna, always comply with the regulations governing the installation of an approved lightning arrester. Such a device is inexpensive ami easily installed.