Project Goal and Purpose
Amplification is necessary for interpreting radio waves, as the audio playback volume is limited by the signal strength of carrier waves.
The principle is to "mix" the weak received radio wave with an external power source. Bipolar Junction Transistors (BJTs) can take an input signal and, if the current at the base terminal is above a certain value (a cutoff), the base current (Ib) controls the collector current (Ic) proportionally. The ratio between Ic and Ib is the gain (amount amplified).
Essential notes:
- BJTs don’t turn on just because we push a current into the base. Instead, voltage at base must be greater than voltage at emitter must be about 0.7 V.
- Once that voltage drop achieved, current flows, and the transistor can amplify.
- To get voltage drop, we can use biasing. Resistors (usually in the base and collector circuits) will force a reduction in current and a drop voltage, so the transistor stays in its active region, not off.
As an exercise, I built my own simple class A amplifier in Falstad. I picked a 5V input (i.e from an iPhone lightning port) and another 5V Vcc.
I used this post as reference for component values and calculations:
