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From what I understand with VHF, if the signal hits an object, there is a hiss or a dropout. With UHF, the signal either goes through the object or goes around it. It’s probably also a cleaner signal. Azden’s UHF has 63 selectable channels versus the VHF’s 2 channels.
VHF and UHF are both line-of-sight, so any in-line objects will attenuate the signal. VHF tands to have some problems, though. First, and most problematic, is that the VHF frequencies are shared with other FCC licensees on a secondary basis.
Yes. You need a license for a wireless mic unless it operates in the 49 MHz, AM/FM broadcast, or 902-928 MHz band. [Part 15, 90.113, 90.265(b)]. (Note, broadcast news and sports have discrete frequencies to use that are individually licensed).
But, I don’t know anyone outside of the broadcast industry who has ever applied for one nor been busted for not having an FCC license.
The second reason that VHF should be avoided is because to get true diversity receivers, you need the antennas to be at least 15-inches apart. (1/4 wave length – 6-inches for UHF). Since you cannot buy a true diversity receiver for VHF, they will always be subject to dropouts and hiss.
UHF wireless mics are preferred because even though there are as many, if not more users, the range is shorter and there are more frequencies available, thus the interference potential is far smaller. And you can get true diversity to reduce dropouts.
I do have some VHF FM units that I use only as a backup. (I do a lot of live theater). It’s rare that I get any interference or noise, but I would never depend solely on a VHF receiver.
Ironically, most theater talent mics are VHF-FM.