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Python Radio 11: Power
Let’s get some watts out…
The Raspberry Pi Pico (RP2040) delivers about 3.8 milliwatts of power to a pin (when transmitting at about 7 megahertz). You can (as we will see later) do some amazing things with only this small amount of power. The ARRL has an award you can win called the 1,000 miles per watt award, as does the NAQCC. This is often won by reducing power to levels the RP2040 can reach. Connect your RP2040 to a cheap end-fed half-wave antenna and contact someone 4 miles away and you win.
But many people would like more power. This is where an amplifier comes in handy.
CW is one of the easiest modes to amplify since it is not picky about fidelity. We can use a Class C amplifier and get efficiencies between 75% and over 90%, making it easier on batteries if we go portable.
To make our amplifier, we will be using an RF power transistor. Specifically, a cheap 2SC2078 transistor.
We will use our transistor as a switch. Our transistor has three pins, called the base, the collector, and the emitter. The collector is connected to the positive side of the battery. The emitter is connected to the negative side of the battery. If we put a small positive voltage on the base (such as the 3.3 volts from an RP2040 pin), the transistor will turn on, and get quite hot as it shorts out the battery. So we won’t…
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