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.

Today I modified my 6-band homemade SDR receiver to get a sampling clock from an OCXO. I also put WSPR-15 decoder running on 160 meters to see if there's any activity. At least the frequency stability should be good enough now.