If you're trying to decide on which one, the bands of VHF are often more used, increasing the chance of 'crossed' signals. UHF systems have a bit more freedom in attaining an uncluttered signal that facilitates the process.
Each type functions pretty much the same way: The microphone sends an analog audio signal, which then modulates the impulses into RF and projects it to a receiver. The receiver then demodulates the RF, turning it back into an analog signal.
Here we'll take a look at the devices used. For a demonstration purposes we'll use a body-pack transmitter and a lavalier mic; of all the kinds of mic systems, this likely the most widely used. The lavalier microphone connects to the transmitter via a mini plug and again, transmits to the chosen frequency on the receiver.
Most receiver units have an male XLR cable for connecting it to a PA or recording input. There are many units that have both an XLR and 1/4' jack. You have two ways to connect, depending on the standard of the amplifier or mixer.
A couple of things you'll probably want to consider are a low battery indicator on the transmitter unit and a monitor display for showing you want frequency band you're running.
Let's take look at our tips for operating a wireless system:
1. A clear line of sight between the components is certainly beneficial. This adds to the likelihood there'll be a better connection from transmitter to receiver with a minimum of interference. It's still important to note that wireless transmitters can penetrate walls or around other obstacles, even if it diminishes the reception somewhat. Give it a try and see. If it's satisfactory use it. If not try another frequency. (You won't have that liberty, lest you have a USB system that has the ability to scan frequencies).
2. A useful tip concerns the battery and how much juice it has left. It's wise to check the level of the battery power, but most importantly to carry a backup or two. It would be a pity to run out of juice with no back-up.
3. When choosing a wireless mic receiver try to get a 'diversity' receiver. If you're in a close space, the radio frequencies can rebound off the walls. The difference in timing can result in canceling the radio waves creating a drop-out. A diversity receiver has 2 antennas and 2 demodulators. With 2 points of reception the signals will be received at minutely different times so the two antennae alternate and pick up the better reception.
These few tips and tricks should help to make the most of your experience with a wireless microphone system.