Radio broadcast .. (1922-30)

328 Radio Broadcast slightly or reduce the filament or incline the rotor slightly and try again. If this test does not produce a carrier wave, then remove a few turns from the tuner coil or try another tap on the stationary coil of your variocoupler (if the latter is used), and try again. With the ordinary antenna and a .001 condenser in series as shown in the diagram, the broadcasting stations should be heard with about 40 to 60 turns of wire on the tuner. In some cases you may require only 35 turns. Turn the condenser slowly, as the broadcasting stations require very sharp tuning when at any distance. After you have obtained an approximate setting with the .001 condenser you will find that the vernier in shunt with it on the vernier attachment will give a much closer setting. While you are experimenting with this 'set, your tube will be occasionally in a state of oscillation. Much has been said about the interference that one creates in tuning a regenerative set. Don't let that worry you. The output of a detector tube will not split anybody's ears. The fellow who is using four or five hard tubes in an amplifying circuit is the fellow who hears your little wave and usually he is the fellow who is creating all the interference with the tuning of his set. Let the blame rest where it belongs — on the fellow who is using five-watt power tubes in his receiving circuit. If you try to tune in a distant station without oscillating you will never get anywhere. You can pick up that carrier wave a dozen times easier than you can his music or voice. Now we shall suppose that you have succeeded in picking up a carrier wave after altering your coils until tuned within the proper range for broadcasts. At the centre of the wave you will hear something that bears a distant resemblance to music or a man's voice that sounds more like the barking of a dog than anything "else. Your next problem is to clear it up and amplify it. You will now have learned that your hand has a capacity effect. While you have your hand on the condenser dial or knob you hear the carrier wave, but when you take your hand away it is gone. Your hand affects .the tuning by increasing the capacity. You will therefore find that by increasing the capacity of the condenser till you cannot hear the wave, it comes in when you take your hand away. By experience you will learn just about how much capacity effect your hand has and make an allowance for it. Then you learn another thing. You have the carrier wave tuned in at last and now you seek to clear up the music by inclining the rotor of your coupler, or by separating the two coils (if tuning with them), and you find that this also affects your tuning. When the coils are close together or. when the rotor of the coupler is horizontal or nearly so, a slight change in the coupling causes a decided change in the wavelength of your receiver. As your tuning coil and tickler coil are placed farther apart (or as the rotor is inclined toward the vertical) the detuning effect of the movement becomes less pronounced. It is therefore easier to tune and adjust the tickler control simultaneously when the coupling is rather loose, provided that the set is so constructed that oscillation can be obtained with a fairly loose coupling without crowding the filament. As stated before, the oscillations occur more readily at low capacity in the aerial than at high, as a usual thing. Therefore, on rotating the condenser to decrease the wavelength, the set breaks over into self-oscillation. It may do this very gradually, beginning with a slight hiss, or it may do so with a sudden popping sound in the receivers. The latter state is difficult to control and causes a great deal of trouble in tuning. It is usually due to operation at too high a filament temperature. Reduce the filament temperature until the oscillations are set up gradually with change of capacity. Having established these conditions, you are ready to tune in the broadcasting station. A distant station may be tuned in systematically by the following method. Increase your condenser capacity until the removal of your hand leaves the upper or high wave portion of the carrier whistle in the receiver. Then incline your rotor until you pass through the centre of the wave and beyond to the low-wave half of the whistle. Again increase your capacity until you are set on the upper half of the wave. Incline the rotor (or separate the coils as the case may be) until you are again on the lower half of the wave. As you alternate from one side of the wave to the other in this fashion the wave becomes more and more pronounced and the music or speech at the centre becomes louder and clearer. You are approaching the point of regeneration.