Fun with Software-Defined Radios: Mapping the Spectrum in the Mission, SF

Beep
Beep
Sep 9, 2015 · 11 min read
The BladeRF and RTL-SDR

The radio

Our setup

Full spectrum with peaks at each center frequency
Detail of 1.7GHz-2.2GHz (cellular) with peaks at each center frequency
“Light” averaging; peaks are still present
More aggressive averaging; peaks nearly gone
Even more averaging; peaks are gone and spectrum is stable
Bin size too large; useful data has been suppressed

The app

Courtesy of NTIA, U.S. Dept. of Commerce / Public Domain
Oh, I’ve seen this episode before!
“Johnson, I think someone is eavesdropping on us…”

What we learned, or: What not to do.

A 2GHz 1/4-wavelength planar elliptical dipole antenna, AKA two pennies soldered to a coax cable
Before (blue) and after (red) switching antennae
Interference of two circular waves, by Wikipedia user Bgks / CC-BY-SA

Future directions

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http://www.thisisbeep.com

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