I might have missed it, how does OP broadcast across 80mhz with a 20mhz SDR? I think my mental model about SDR capability is wrong, does sample rate not necessarily gate the range at which an SDR can TX/RX? Really funny idea!
The FM band, from 88 to 108 MHz, is 20 MHz wide.
You’re right, I can’t believe I actually failed to mental math that subtraction problem correctly!