Appendix 3
Short Alignment Procedure for Superheterodyne Radios

IF Transformer Alignment

With a modulated 455-kHz signal, place the signal generator’s output via a wire near the antenna coil or loop antenna. Set the variable capacitor to maximum capacitance or fully closed. With the earphone or loudspeaker, listen for the modulating signal and adjust each of the IF transformers for maximum volume.

Oscillator Coil and Trimmer Capacitor Adjustments

With the variable capacitor’s trimmer capacitors for the RF and Oscillator sections set to half capacitance, provide a modulated 540-kHZ source (or 537-kHz source from Chapter 4) by coupling a wire near the antenna coil or loop antenna. Set the variable capacitor to an almost fully closed position with about 1 to 3 degrees of arc from the fully closed position. Adjust the oscillator coil for maximum volume. Then if possible, slide the coil of the ferrite bar antenna to adjust for maximum volume. If an RF transformer is used, adjust the RF transformer for maximum volume.

Now, set the test generator to 1600 kHz (or use the third harmonic of 537 kHz = 1611 kHz) with modulation. Readjust the variable capacitor to near minimum capacitance, or about 1 to 5 degrees of arc from the fully open position. Adjust the oscillator trimmer capacitor for maximum volume. Generally, the RF trimmer capacitor will not be set to an optimum for the low and high end of the AM band unless there is a back and forth adjustment between the oscillator coil, oscillator trimmer capacitor, and RF coil or antenna coil, etc. Therefore, as a compromise, one can adjust the RF trimmer capacitor for maximum signal strength as desired by the operator. That is, the RF trimmer capacitor can be adjusted for maximum signal at the mid band, the low end of the band, or the high end of the band. No generator is necessary, just tune to a station in the desired portion of the AM band and adjust the RF trimmer capacitor for maximum volume.