Hmm. Maybe someone can debunk this idea: Could it have been some harmonic frequency of a terrestial lower frequency radio signal (such as 710MHz) that bounced

Hmm. Maybe someone can debunk this idea: Could it have been some harmonic frequency of a terrestial lower frequency radio signal (such as 710MHz) that bounced off ionosphere? That frequency range is currently assigned to mobile, but I suppose it could have been in TV/Broadcast use back then as it's right next to that spectrum. TV broadcast truck?