Converting RF to DC with a Raspberry Pi: Building and Troubleshooting an Envelope Detector

Adding an Envelope Detector to Convert an RF Input to a DC Output

I attached the ADC Pi module to the GPIO header and stacked the DDS module directly on top, using PCB support spacers to keep the two boards together and relieve strain on the GPIO pins.

The next step was to turn the RF signal produced by the circuit under test into a DC voltage that the ADC Pi could read. This is where a simple envelope detector comes in.

A classic envelope detector consists of just three components: a diode, a capacitor and a resistor. The RF input (Vi) is fed into the detector, and the DC output (Vo) is taken from the other side. In theory, the input RF (shown in blue) should produce a smooth DC voltage (shown in red).

When I first built the detector, the output was nearly flat. After measuring, I found the peak RF voltage from the test circuit was only about 0.2 V (200 mV). That tiny signal was the culprit.

Diodes require a forward‑bias voltage to conduct. A standard silicon diode needs roughly 0.7 V, while a germanium diode needs about 0.25 V—both higher than the 0.2 V peak I was working with. Consequently, the detector never fully turned on, and the DC output stayed near zero.

To overcome this, you can either use a Schottky diode with a lower forward voltage, add a small pre‑amplifier stage, or increase the RF source power. With the right components, a Raspberry Pi‑based envelope detector can reliably translate RF signals into readable DC voltages for data logging.

For more detail, see A Slice of Raspberry Pi.