That would appear to rule out 2nd harmonics of a broadcast atsc tv station, as I would expect the carrier to be 0.620 above the bottom edge.
For grins, I just tuned around the second harmonic region of several very strong local channels using my Icom 8500 and found nothing... I suspect that the broadcast channels are fairly clean.
This is a real head scratcher, but I am leaning toward ham experimental transmissions.
jr
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