Radio broadcast .. (1922-30)

526 Radio Broadcast especially true in the case of the detector tube. Change around the tubes until their best operating position is found. 3. Manufactured and home-made coils may be so mounted that the direction of winding in several of the coils is found to be opposite. Check over the coil assembly and be sure that TROUBLE SHOOTING IN THE CRYSTAL REFLEX RECEIVER T I HE use of good, tested crystals in the RADIO BROADCAST Knockout crystal reflex receiver cannot be emphasized too much. Poor crystals will cause squealing due to regeneration FIG. 5 THE N-P COIL PLACED OVER THE SECONDARY all the coils are mounted so that the winding direction in all the coils is the same. 4. When regeneration does not occur, it is an indication that the tickler coil is reversed. Also, the B battery voltage on the detector tube may be too low. On the other hand, if regeneration is too pronounced, the circuit going in and out of oscillation with a decided "plop," it is quite evident that excessive detector plate voltage is being applied and must be reduced for more stable operation. 5. Howling may be due to (a) an interaction or feedback between the several circuits; (b) Reversed leads to the primary of the audio reflex transformer, (c) Incorrect values of C battery. In some cases it will be found necessary to ground the negative side of the A battery to obtain stability. 6. Grid leaks clear up, to a marked degree, the volume and tone quality delivered by the receiver. Try various values of leak and grid condenser. 7. The spiderweb coils; as designed, will cover the entire broadcasting wavelength when the secondaries are shunted by .0005 mfd.. variable condensers. When the sensitivity of the receiver varies for different wavelengths, that is to say, when signals received are louder on the lower wavelengths than on the higher wavelengths, the receiver is then in a condition where the step-up of energy is not the same over the entire wavelength scale. To overcome this, the primaries and secondaries of the two couplers must be made semi-variable so that resonance may be obtained at all the. wavelengths. Variation of the turn-ratio between primary and secondary will also serve to eliminate this trouble. 8. The use of a by-pass condenser shunted across the C battery and secondary of the audio reflex transformer as outlined in the November GRID is not a general cure-all for poor volume output. In a majority of cases this procedure does "tone up" the receiver quite appreciably. This usually depends upon the value of C battery and type of audio reflex transformer used. CENTER TAP FIG. 6 produced by a high resistance contact on the crystal This condition also causes body capacity effects re. suiting in unbalanced operation. It is essential that the negative side of the A battery be grounded. It would be well to have the negative side of the A and B battery connected together, thus providing a common ground for both BUZZER FIG. 7 batteries. In some cases, due to internal characteristics of the receiver this does not work out well and it is necessary to connect the negative B to the positive A post. A CIRCUIT FOR CODE PRACTICE THOSE who have a longing to know the code used in radio communication will find the circuit shown in Figs. 7 and 8 useful in the practise of sending and receiving dots and dashes. The system is especially applicable to Radio Clubs,