Yesterday, during OsmoDevCon 2018, Steve Markgraf released osmo-fl2k, a new Osmocom member project which enables the use of FL2000 USB-VGA adapters as ultra-low-cost SDR transmitters.

How does it work? A major part of any VGA card has always been a rather fast DAC which generates the 8-bit analog values for (each) red, green and blue at the pixel clock. Given that fast DACs were very rare/expensive (and still are to some extent), the idea of (ab)using the VGA DAC to transmit radio has been followed by many earlier, mostly proof-of-concept projects, such as Tempest for Eliza in 2001. However, with osmo-fl2k, for the first time it was possible to completely disable the horizontal and vertical blanking, resulting in a continuous stream of pixels (samples). Furthermore, as the supported devices have no frame buffer memory, the samples are streamed directly from host RAM. As most USB-VGA adapters appear to have no low-pass filters on their DAC outputs, it is possible to use any of the harmonics to transmit signals at much higher frequencies than normally possible within the baseband of the (max) 157 Mega-Samples per seconds that can be achieved.

osmo-fl2k and rtl-sdr Steve is the creator of the earlier, complementary rtl-sdr software, which since 2012 transforms USB DVB adapters into general-purpose SDR receivers. Today, six years later, it is hard to think of where SDR would be without rtl-sdr. Reducing the entry cost of SDR receivers nearly down to zero has done a lot for democratization of SDR technology. There is hence a big chance that his osmo-fl2k project will attain a similar popularity. Having a SDR transmitter for as little as USD 5 is an amazing proposition.