I have an interesting case to report.
I am receiving a beacon on the KiwiSDR, iding as K1MS. It's actual transmit frequency is 50.063 MHz. Both the beacon op and I confirmed with a separate receiver (he a PROIII, me a IC-706) that this is not a real signal but more a case of intermod.
My setup is a delta loop antenna down to a PolyPhaser arrestor at the building entry, then an Array Solutions AS-RXFEP receiver protector, then into a shielded enclosure with an additional Mini-Circuits SLP-70+ low-pass filter on Kiwi antenna port. Lambda linear supply. All in a barn with little else.
Looking at the simple sum and difference, its either 33.460 or 66.666 MHz.