Page 30 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

right. The other alignment tool at the bottom of the figure is suitable for adjusting

the inductor, but its blade is too thick for adjustment on the poly-varicon.
Test Generators

The radios shown in this book generally will not need test generators or test
oscillators. Chapter 3 will show how to make two inexpensive test generators.
However, buying a test generator or a test oscillator is always a good investment.
A function generator is a useful device because it will provide not just sine waves

but usually triangle and square waves as well. Some will provide variable-duty-cycle
pulses, and some also will provide an amplitude-modulated (AM) signal (Figure
2-2).

FREQUENCYI
STOP FREQUENCYC .. z1
•
POWER

FIGURE 2-2 Function generator.

The function generator in the figure will produce waveforms from almost DC (direct
current) to 2 MHz, which covers frequencies of the broadcast AM band plus the
amateur radio 160-meter band. It also has an amplitude modulator. Thus, once a
radio is built, this generator can be used for alignment and testing purposes.

Inductance Meter
An inductance meter is very handy to have around because some of the inductors

for the radio projects in this book may not be available, and alternate inductors
must be modified. An inductance meter allows hobbyists to wind their own coils
and measure their inductances. For example, using normal hookup wire, one can
wind an antenna coil to the correct inductance via an inductance meter. An
inductance meter a!lso can measure the value of unmarked coils, which then allows

the hobbyist to determine the capacitance of a matching variable capacitor. Figure
2-3 shows an inductance m!eter measuring an inductor at 132.5 ~H.