Tony DiCola's Freq Show Turns Any Raspberry Pi and RTL-SDR Dongle Into a Signal Visualization Tool
Compatible with Raspberry Pi boards going right back to the original Model B, this project gives you insight into the invisible world of RF.
If you've ever wished your eyes could see outside the boring spectrum of visual light, Tony DiCola's Raspberry Pi-powered project may be of interest: the Freq Show makes invisible radio signals visible, putting a colorful live-view waterfall or frequency graph on a compact display.
"Software-defined radio (SDR) is a great tool to explore radio signals using a computer and inexpensive radio tuner," DiCola writes in his recently-updated tutorial on the topic. "With SDR you can examine many radio signals such as FM radio, television, emergency & weather radio, citizen band (CB), wireless protocols, and much more."
While SDR devices can be expensive and require a relatively powerful device to drive them, DiCola's Freq Show is designed to be low-cost. The hardware is simple: Any model of Raspberry Pi single-board computer, with DiCola's first version of the build using an original-model Raspberry Pi Model B with its since-retired 26-pin general-purpose input/output (GPIO) header; a 3.5" 480×320 color touchscreen add-on or official Raspberry Pi Touch Display; and the affordable receive-only RTL-SDR dongle.
"Once the program loads," DiCola explains, "it will start by displaying an animated frequency graph, and menu of options. The graph displays the intensity of radio signals (measured in decibels) across a range of frequencies. The taller a peak on the graph, the higher the intensity of the signal at that frequency.
"Another useful way to visualize radio frequency data is with a spectrogram that shows the intensity of the signal over time," DiCola continues. "Each row of the plot represents a point in time, and each pixel color in a row represents the intensity of the signal at that frequency. Pure blue pixels are the minimum intensity, pure red pixels are the maximum intensities, and a gradient of blue-cyan-yellow-red represents in between intensities."
A full guide to using the Freq Show — which, DiCola takes pains to point out, merely graphs the signals and makes no attempt to decode them into audio — is available on the Adafruit Learn portal now.
