FM radio reception on shortwave bands

[dewdude]

I live about 5 miles from a NOAA station on 162.55mhz and, occasionally...I will get an image of it down around 21mhz.

If you've got really strong signals making in to your receiver...you can get stuff like this. It could be hetrodyning with a local oscillator...if you've got one in the radio running that high. In older radios it's usually 10mhz; my IC-725 transceiver from the late 80's has an IF running in the 70mhz range; but even then I don't often hear broadcast FM imaging.

You can also get hetrodyning from adjacent strong signals as well.