Radio age (Jan-Dec 1924)

24 RADIO AGE for December, 1924 A photo-diagram showing the ideal dimensions for the antenna to be used on any average broadcast receiving set. If the instructions printed on the diagram are followed religiously, the listener can expect very good results from practically any receiver he tries out. ASRIAL T^HE way to learn radio is to build a -* few receivers. No amount of study, no pouring over theories, will teach you adequately. It is interesting to hear a station a thousand miles away on some other man's receiver, and it seems marvelous enough. But it is ten times as thrilling and ten times as marvelous, when you pick that distant station up on a set you have built with your own hands! Before attempting to construct any of the circuits recommended, you should know a few of the fundamental principles which must be adhered to in order to obtain maximum results. Antenna and Ground \ CHAIN is no stronger than its -^* weakest link, and radio reception, no matter how good the receiving set may be, cannot be satisfactory without a good antenna and ground system. The most efficient antenna is an outdoor aerial fully described in accompanying drawing of an "ideal antenna," into which pages of instruction have been compressed. Be sure your "ground" conducts electricity deep into the ground. A water or radiator pipe (not gas pipe) serves the purpose well. File or sandpaper the pipe, tighten copper clamp tightly to it; solder clamp to your ground wire. If you are in doubt about the effectiveness of your "ground," use two grounds. One fan who has picked up 267 stations actually uses four different kinds of grounds. Since it is a fact that the energy gathered by the antenna is generally but a trifling fraction of a fly-power, you want the set you build to be the last word in sensitiveness and efficiency. Otherwise you in effect move your station many miles farther away. A dollar saved through buying a cheap condenser, for example, may cost you 1000 miles of distance. If we analyze any circuit, we find three fundamental factors which determine the efficiency of the particular circuit selected; namely, inductance, capacity, and a rectifying device. The coil or coils constitute the inductance; the condensers (fixed or variable) the capacity; and a crystal or vacuum tube the rectifying device. The Inductances TN the selection of a really efficient coil -*■ or coils for inductance, several factors must be borne in mind. First, Insulation. Since the flow of current in a coil occasions the sending out of "lines of force" (which constitute a "magnetic field"), you should have the least possible insulating or supporting material about it. Rubber, phenol compounds, compositions, fibre, etc., produce a loss of energy through absorption. Second, the Method of Winding. Layer windings on a cylinder, because w Switch HOOKUP NO. 1 TWO CIRCUIT CRYSTAL RPCE/VE/? C&V57XL Pfl— MOYAgLF COIL mEDCOND 0O1S4F o.ooos/*r "3H tOBMB/S COHDENSEI? The Magazine of the Hour QThe Best Way to Lies in Building HOW To Your SIMPLE By EDMUND successful application of this form of inductance to the Reinartz circuit, led to the construction of new and perfected variometers, variocouplers and the recently developed three-circuit lowloss tuner. In these tuning units, we find an absence of absorptive (or dielectric) material. Even the spiderweb or wooden frame is eliminated because it absorbs energy, and the coils are made selfsupporting with a special low-capacitative cement. "Distributed capacity" between the windings has been eliminated. The disc shape of the windings produces flat "magnetic fields" in which the lines of force are concentrated and do not reach out and interfere (i.e. generate disturbances, howls, etc.), with other parts of the set. As the coils are only a quarter of an inch thick, all turns of wire are included in the mutual "fields." This is not the case with tubular or honeycomb coils where the far turns of one coil may be removed several inches from the coil to which it is coupled inductively (i. e. joined through the electromagnetic action of the "fields.") 6ROUND ■== ACtE HEAW LIVES SHOW ACTUAL CONNECTIONS or SET -LIGHT LIH£S SHOW ACXESSOPIES the adjacent turns of wire are close and parallel, give a wasteful condenser effect. This loss is called "distributed capacity" and it acts as a resistance to the incoming signal. Third, Coupling. The method of coupling the "magnetic fields" when two coils are used, is important, as will be explained. Carl Pfanstiehl, physicist and inventor, who has made a life-long study of electromagnetic forces including the electrical exploration of the "fields" about all types of windings, has found the staggarwound form of inductance to be the most efficient for radio reception. The Capacity HPHEREis no use to use a -* low-loss inductance, however, if you hook it up to a high-loss condenser. All insulating material should be kept down to a minimum, and what little of it is used must be located as far outside the electrostatic field as possible, since any electrostatic lines of force which pass through insulating materials absorb energy from the circuit. (The loss takes place in the form of heat.) The surface of insulating materials collects a little dust and sometimes a thin film of moisture. If this leakage path is short and wide, considerable energy will leak across, instead of being stored up in the condenser. The fixed condensers, since they generally must be accurate and must be made of the best insulating material,