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Osmo-FL2K – The RTL-SDR’s Other Half

An interesting new development has sprung out of the wonderful Osmocom project: a low-cost, wide bandwidth SDR transmitter that works with GNURadio. How low cost? How about $10?

This is all possible thanks to the wonderful work of Steve Markgraf, an Osmocomm developer who found that when properly coerced, a cheap USB3.0 to VGA adapter will output raw samples straight from its RGB output lines. While the base sample rate of the dongle, using the FL2000dx VGA chip, has a normal max frequency bandwidth of 150MHz, it was found that since the output is essentially unfiltered valid signals can be output on any desired harmonic. GSM site spoofing, as well as GPS frame transmission have already been proven using simple GNURadio block diagrams.

Raw output spectrum of the dongle – not exactly FCC compliant!

Obviously in its raw, unfiltered state, this dongle has limited appeal in the amateur world for practical applications. Harmonics of the signal will be abundant and loud; sometimes nearly the same amplitude as the fundamental. But with some more development and proper filtering, this could be the beginnings of a low-cost transmitter and a perfect complement to the RTL-SDR series of receivers. I’ve got a dongle and some complementary accessories on the way now, and you can bet I’ll be playing around with it soon.

Stay tuned and 73!

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