It Works!
Recorded some shortwave with rtl_sdr defaults: rtl_sdr -f 111730000 AM_111730000_3.iq
China, lots of fading, some Russian I think, music...
Just a few seconds (10 or so) as the files get really big at 4 MB per second, and this is only a small SDcard. I recorded on the laptop, scp the file to the Raspberry, then play it into the Anything Transmitter board: root@raspberrypi:~/compile/pantel/send_iq# ./send_iq -f AM_111730000_3.iq -l
Checked playback with scope on I/Q, signal still clips a bit, checked spectrum with xpsa at 1.5 GHz, looks normal... but HEY, when I play it back on the laptop: rtl_fm -f 1575420000 -M -s 12000 -l 0 - | play -r 12k -t raw -e signed-integer -b 16 -c 1 -V1 -
then I can tune several stations by tuning the 1.5 GHz VCO.
BTW 'rtl_fm' with the -M flag is really AM.
So, everything works, VCO is stable enough to hang on a few kHz at that 1.5 GHz for long enough to listen and ID a station.
So, next is digital TV. Do not hold your breath did a lot of steps this week in a very short time.