# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DdWnDrDgKzX
- **Gondola URL:** https://gondola.cc/posts/70577846-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/8cc77cb8a0.jpg
- **Posted:** 2026-09-16T15:31:50.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Radio waves and visible light are the same phenomenon, separated only by scale. Green light oscillates at roughly 550 terahertz. The FM station down the road runs at 100 megahertz, a wave three metres long. Your retina has no receptor for it. A USB stick the size of a lighter does.

The NESDR SMArt is an RTL-SDR, a repurposed European digital television receiver. The signal path is worth following.

- The antenna converts a passing electric field into a current, microvolts of it
- The R820T2 tuner amplifies that current and mixes it against a local oscillator, sliding a chosen slice of spectrum down to a low intermediate frequency
- The RTL2832U samples that slice with an 8-bit converter and outputs in-phase and quadrature streams, the I/Q pair that encodes amplitude and phase together
- USB carries raw samples to the host, and every decision after that point is software

The specification is honest about its limits. Coverage runs 100 kilohertz to 1.75 gigahertz, with everything below 25 megahertz handled by direct sampling. Instantaneous bandwidth reaches 3.2 megahertz, though 2.4 is what runs without dropped samples. Eight bits yields a theoretical 49.9 decibels of dynamic range. A 0.5 PPM temperature-compensated oscillator holds tuning to within 545 hertz at 1090 megahertz.

Seeing happens in the fast Fourier transform. The host slices the sample stream into overlapping windows, transforms each into a spectrum, and paints the result as a single row of pixels: frequency across, time downwards, power as brightness. Stack thousands of rows per minute and the invisible becomes a photograph. Aircraft transponders at 1090 megahertz appear as vertical hatching. Weather satellites at 137 megahertz sweep past as a Doppler-curved smear.

Antti Palosaari discovered in 2012 that the chip would surrender its raw samples. An entire hobby followed.

Radio was always visible. It simply needed the right eye.

#stemantics #sdr #rtlsdr #radiofrequency #electricalengineering

## Stats

- **Views:** 3,723
- **Likes:** 51
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## Tags

sdr, electricalengineering, rtlsdr, stemantics, radiofrequency

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