There are times where radio propagation is absolutely horrid, and even the best of equipment will get nothing but static. Back last month, we had a geomagnetic storm that just wrecked havoc on the HF bands. Unlike VHF frequencies used in the continental ATC centers, HF signals can vary greatly depending on the time of day, sunspot cycles, ect. In most cases, VHF tends to keep the same range of reception.
Ken