Radio broadcast .. (1922-30)

Cave-Man Stuff, But It Works 327 cardboard tube. Wind fifty turns of No. 26 or No. 28 wire around one, tie the ends around the rings, and leave about a foot or more of wire at each end for connections. Around the other wind about sixty turns and secure in the same way leaving leads for connections. Screw two curtain pole brackets into the end of the table, lay a piece of broom pole across them and hang the two coils on the pole (see photo, p. 329). Set four binding posts into the edge of the table and fasten these four coil leads between the bolt head and washer of the binding post, leaving the binding post for other connections unless you wish to tie more than one wire into the clamp of the post. This tuner is very satisfactory and will cost about 50 cents to 75 cents. Use the 5o-turn coil for a tickler and the 6o-turn coil for a tuner. After testing the set you may find that there is too much wire on the tuner, in which case remove a few turns at a time while testing. Connect the other apparatus as shown in the diagram. Increase the brilliancy of your filament until a slight hiss is heard. Decrease it till you are just below the hissing point. Do this with your two coils at extreme ends of the pole or with rotor of variocoupler vertical. Bring the coils together. Rotate your condenser plates and you may hear the tube oscillating. The oscillation of the tube usually takes place more easily at the low capacity end of the condenser, or in other words with the condenser nearly open. This is the primary consideration for the beginner if he must tune in long distance stations. The tube must oscillate with the coils close together. When the tube is oscillating there is a mushy sound in the receivers, something like a faint rushing of air. The static noises become louder as the point of oscillation is approached either by turning the condenser or moving one of the coils back and forth. Spark signals, if heard, will usually be clear and more or less musical with the tube quiescent, but become hissing noises when the tube is oscillating. If the tube does not oscillate under this test, then turn one of the coils around and try it again. Instead of turning a coil around you may exchange the two connections to one of the coils. If you are using a variocoupler, make the test with the rotary coil horizontal and if you do not hear the tube oscillating, turn the rotor completely over and try again. Occasionally you get a tube that does not oscillate with the usual hook-up. In that case increase the grid condenser to .001 by substituting a fixed condenser of that capacity. You may use the one shunted across the telephones for the grid and replace the phone condenser with one of about .0005 mfd. capacity, also fixed. Oscillation will usually be obtained with a relatively low filament current with these latter capacities. However, do not fail to try it with the rotor MR. TANNEHILL/S SINGLE-CIRCUIT HOOK-UP With which he has heard stations over 1,000 miles away, with one tube inverted (or with the coils reversed). Once you have learned how to produce the oscillations it is but a short time until you have learned to control them by changing the filament brilliancy or turning the rotor, or if coils are used, by moving one of them back and forth on the pole. Occasionally there is almost a total absence of static, spark signals, or other sound, so that it is nearly impossible to determine whether or not the tube is oscillating. This is rare, however, at the present time when there are so many broadcasting stations and amateurs. The second step is to tune in a telephone station. With the tube oscillating, turn the condenser around very slowly and listen for a whistling note. This is the carrier wave of the broadcasting station. As you change the condenser capacity you come upon a high-pitched whistle. As you turn further the pitch of the whistle becomes lower and lower. As you turn on, the whistle repeats itself becoming higher and higher in pitch until it disappears. At the centre of this double wave you will perhaps hear music or voice. If you do not hear the carrier wave, separate your coils