We have now added a monochrome OLED screen (SSD1306) to the Uno, simply plugging the I2C pins directly into the board and bending SSD1306's the GND and VCC pins and connecting them with wires. The setup is powered with 4 AA batteries via the jack.
This allows a much more versatile use of the device since it can illustrate the signal dynamics at different signal levels. The previous version only used the built-in LED and only reacted when the input was above a hard-coded signal threshold. That was for instance useful to find electrical wires in the wall.
Initial experiments with the new functionality and a hand-held radio emitter showed that the strength of the EM field depends on: