Radio broadcast .. (1922-30)

Radio Broadcast positive reactance is also greater (remember they must always balance). How can the positive reactance increase to meet this negative increase? By increasing the* inductance or frequency, or L and f in the formula XL = 2^fL. But we have said that the honeycomb coils, or L, are no/t to be changed, so that leaves f, or frequency, as the only possible variation. Therefore f must rise, and so it does until the increasing positive reactance equals the negative reactance which rose when the primary condenser was lowered. But when the frequency rises the wavelength comes down. Thus lowering the capacity in a condenser decreases the wavelength. The reverse is equally true and obvious, i. e., the condenser capacity increases, TO PHONES 01 AMPLIFIED FIG. I. Diagram for a three-con honeycomb set. For best operation, the primary, secondary, and tickler coils should be comparatively large, the tuning being done with condensers Ci and C2, the latter should be of small capacity, as outlined under "undesirable effects, of capacity" the negative reactance is lowered, and to lower the positive reactance to the same value, the frequency must come down — and the wavelength rises. The effect of varying the inductance in the circuit is also easily followed in the same manner. If the inductance is increased (perhaps more turns of wire are put into the circuit by means of taps), the positive reactance is increased in accordance with the formuja Xl=2xfL. Therefore, at the new resonance point the negative reactance must also be higher. But; as the condenser or capacity is not to be varied, the frequency must drop (lowering the denominator of the fraction in XC = 2T?t) or the wave rises. Hence increasing the inductance in a circuit increases the frequency of wave. UNDE6IRABLE EFFECTS OF CAPACITY THAT is all there is to the mystery of tuning, and a comprehension of the foregoing will be of value to the experimenter in showing the true functioning of capacity and inductance as no analogy or less scientific explanation could do. A little thought will now indicate why it is desirable to eliminate all stray capacity from a circuit. In the circuit of Fig. i, the strength of the signal depends on the E. M. F. induced across the coil, or between the terminals Y and Z. The larger this coil, or the higher the inductance, the greater will be this E. M. F. and the strength of the received signal. Hence it is always best to increase wave by means of inductance rather than by shunting with capacity, On a honeycomb set, experienced operators always use the largest coil permissible for a given wavelength, keeping their condensers as near to the zero point as possible. For this same reason, shellac, and similar adhesives which, through their dielectric qualities, increase the distributed capacity, are eliminated from efficient windings. The. honeycombs and duolateral windings, the spider webs, etc., were all designed and invented with the idea of decreasing capacity and permitting a higher value of L for a given wave. Professor Hazeltine has developed the neutrodyne system with the same purpose in mind. Short wave radio frequency amplification had been impossible for many years due to the high capacity between the elements of the vacuum tubes boosting the waves, so that not sufficient inductance could be used for an efficient transference of energy.