Transmitting WSPR on osmo-FL2K

I've been recently transmitting WSPR on an FL2000-based VGA adapter, using the osmo-fl2k library to use one as a fast DAC. I initially didn't get any spots, but after adding a small amplifier of about 100 mW, started getting spots on all bands from 160m to 20m.

Now I tried it without an amplifier into a bit longer random wire antenna, and finally got some spots "barefoot" on 40m! That's just 2 mW from the VGA port into an antenna through some low pass filtering and matching.

Frequency stability seems to be good enough for HF, since the drift values were mostly 0 even on 20m. Initial frequency error was 143 ppm though, so calibration is a must.

So, it's an interesting cheap little transmitter apparently suitable for WSPR as well.
Here's the software used: