Radio mirror (Jan-Oct 1923)

RADIO DIGEST — Illustrated October 6, 1923 RADIO FOR EVERYBODY (Continued from page 11) coil, also air core, but variable. Such a drawing is used to show either a coil from which short leads are brought out at intervals to switch points or a coil which is varied by moving a metallic slider along a rod, the slider making contact with the wires of every turn, the insulation having been removed for a distance of about -fir inch on every turn. Figure 4c specifies that the coil be varied by taps and a switch. In 4d we have a coil wound on an iron core and non-variable. Capacity is another property necessary in a circuit in which Radio frequency currents are to travel. Capacity is the result of having close together two metallic surfaces or wires in which alternating or pulsating direct current is flowing. For a better understanding of this let us consider Figure 5a. Here we have a circuit consisting of a coil of wire (X) and a device consisting of two flat plates about 2 inches square and -fa inch apart. In this circuit, Radio frequency current is flowing and we will consider it at a moment when the current is flowing in the direction indicated. The current spreads out over plate A until the plate is full. If the plate is of the correct capacity, it will become full at just the moment when the current reaches its greatest value and begins to weaken. As plate A is full and plate B contains no electricity we have an unbalanced, unstable condition and plate A discharges or unloads its current back through the coil X and into plate B, as shown in Figure 5b. Electrical current has momentum, just as does a swinging pendulum, and the flow does not stop when both plates are equally charged, but the current piles up in plate B and then must ^ Figure 6 — Three methods of showing condensers on diagrams, one variable and two fixed again flow as in Figure 5a. This action would continue indefinitely and we would have a perpetually oscillating circuit were it not for small losses which occur and the resistance of the circuit. The symbols used for showing capacity in the form of an instrument known as a condenser, are shown in Figure 6; 6a designates a variable condenser, that is, a condenser whose capacity may be varied from maximum to very nearly zero. The unit of measurement of capacity is the farad and its subdivision, the microfarad (.000001 farad). Condensers used in Radio work have very small capacities and are usually measured in fractions of a microfarad; 6b is the usual designation of a fixed capacity, while 6c is another less used method of showing it. As the capacity of condensers is usually written and spoken of in decimals such as .001, .0005 and .00025, Radio men have developed the following way of speaking of them. The Radio experimenter would say "double O one," "triple O five" or ''triple O two five," meaning condensers of .001 of a microfarad, .0005 of a microfarad or .00025 microfarad. Resistance Resistance is, as was stated before, measured in ohms. Since we frequently use resistances of from 1,000,000 to 12,000000 ohms, the Radio fraternity has come to use the word megohm for 1,000,000 ohms and to mention 8,000,000 ohms we would say "eight megohms." Resistances are shown on diagrams by the symbols shown in Figure 7. A resistance which cannot be varied is shown as in 7a, while a resistance that is variable (such as a rheostat) may be specified by 7b; 7c shows a particular form of resistance known as a potentiometer, which is usually connected across the filament battery of a vacuum tube. The sliding Figure 7 — Resistances are shown in these drawings, one fixed, one variable, one of a special unit contact is connected to one of the other elements of the tube (grid or plate), and moving this contact varies the difference in pressure between the filament and the second element. (TO BE CONTINUED) FIRST STEPS IN RADIO (Continued from page 17) caused by too large a tickler coil, is responsible. Also, the grid leak resistance may be too high, causing the tube to block, or the trouble may be due to a too high plate voltage or undesired feedback, caused by the closeness of the plate circuit to the grid circuit leads. Often a steady whistle is heard when a nearby regenerative set emits waves, or if two broadcasting stations are heterodyning each other. Interference of this nature will be recognized by the inability to change the note by tuning, whereas feedback effects are altered by adjusting the tuning controls. Squealing usually is experienced when the amplifiers are switched on and is due to reaction between the plate and grid circuits of the tubes. The most common POSITIVE RESULTS are being obtained by thousands of satisfied users of the EASTERN COIL SETS for the COCKADAY CIRCUIT The remarkable features which are making this circuit (4 circuit tuner) more popular each day are its simplicity of construction and control — wonderful selectivity— distance records — clearness and loudness of reception, and the fact that all capacity squealing, interference, etc., are eliminated. Made as per specifications of Mr. Cockaday, using No. iS wire with D coil bank-wound. COMPLETE ASSEMBLED CS.f^*7C2 SET OF B, C AND D COILS. *P s*. ' «J PRICE ' ' Hook-up, directions and material list free. Mail Orders Filled. Dealers Communicate EASTERN RADIO MFG. CO. 22 Warren Street, Dept. R. D., NEW YORK. N. Y. Dietzen Vernier Condenser 14 Plate $2.65 24 Plate $2.95 46 Plate $3.45 DIETZEN Midget Tube V/i Volt, Operates on one dry cell, either with or without B battery. W i r i n g d i a g ram Free with each tube. $1.00 Socket 40c AMPLET0NE Horn — Nickeled high $3.95 DIETZEN Loop Aerial Set up in 5 minutes. All parts complete Variable condenser, 43 pi. (bakelite end). $1.95 7 Strand aerial wire, 100 feet 65 Argus lightning arrester 95 Reinartz coils ._ 1.45 Dietzen moulded variometer or coupler. £.95 Brandes or Dictograph phones 5.45 Dietzen phones (3000 ohms) 3.75 Rheostat. 6 ohm $ .45 Test Rite battery hydrometer 49 Potentiometer, 250-400 ohm 95 Dial, 2 inch 25 Single open circuit jack k 40 Socket, standard bakelite « 49 Socket, UV-199, bakelite .49 We Pay Parcel Post Charges on All Orders. Money Order or Personal Check Accepted*. Money Refunded If Not Satisfactory. 71 Cortlandt Street Dept. G. NEW YORK America's Greatest Radio Mail Order House cause is the reversal of a transformer winding, in which case it is necessary to reverse the connections to the transformers until the noise is eliminated. When transformers are close together, the squealing often is caused by the magnetic field of one reacting on the other. They should either be completely shielded, or the cores set at right angles. The wiring of amplifier units, when run too close, also will cause squealing and howling. At times a buzzing or humming sound is encountered that is difficult to locate. Often it is due to induction from nearby power lines. It may be caused by a grid condenser made of tinfoil or paraffin paper. In one case, the panel of the set picked up the vibrations from the loud talker through the table, and the vibration was transmitted to the tubes and caused a ringing sound. A plate lead brought close to the ground lead or high voltage leaking' into the aerial circuit is a frej quent cause of buzzing or humming. Unsteady and Wavering Signals Unsteady and wavering signals are due to the unsteady operation of some part of the set. Poor contacts in the filament circuit or an aerial circuit with too low capacity in series with the primary inductance will cause them. Loose inductances will result in unsteady signals, and a leaky aerial or lightning arrester due to rain or moisture will affect the signals. In locating trouble one should bear in mind that the broadcaster is sometimes at fault. The set can only reproduce what it receives, and before blaming the set the operator should tune in another station and see if that acts the same way. In homemade apparatus many factors enter into the operation. For instance, the shielding on the panel may result in feedback effects that cause whistling and squealing. Homemade inductances are often coated with shellac that is unfit for the purpose, sometimes containing water that causes leaks between the turns and poor tuning. Fiber is considered a good insulator as a rule, but it should not be used as an insulator in Radio apparatus. A fiber panel will make any regenerative set noisy, if not worthless for long distance work. Fiber washers should never be used to insulate the binding posts from the shielding on your set. Scrape the shielding away for a quarter inch around the posts or use bakelite washers. (TO BE CONTINUED) Radio communication between Singapore and Christmas Island was established recently. a RED-MEADS" H 1923; 1922 wm Better Radio 'Phones ERE'S what we say about ' 'Red-Heads' '—they're EXTRA-ORDINARY radio receivers. Webelieve they're the best receivers on the market today. Superlatives are easy to say and hard to back up. Here's how we back up ours. We GUARANTEE that you'll like "Red-Heads." You take no risk in buying them. 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