3. UHF vs. VHF

Like the VHF region, the UHF region contains several bands that are used for wireless microphone systems. However, certain physical, regulatory, and economic differences between VHF and UHF regions should be noted here. The primary physical characteristic of UHF radio waves is their much shorter wavelength (one-third to two-thirds of a meter). The visible consequence of this is the much shorter length of antennas for UHF wireless microphone systems. Quarter-wave antennas in the UHF range can be less than 10 cm.There are other consequences of the shorter UHF wavelength. One is reduced efficiency of radio wave human bodies.

This can result in potentially less range for a UHF signal compared to a VHF signal of the same radiated power. "Line-of-sight" operation is more important in the UHF range. Another consequence is the increased amount of radio wave reflections by smaller metal objects, resulting in comparatively more frequent and more severe interference due to multi-path (dropouts). However, diversity receivers are very effective in the UHF band, and
the required antenna spacing is minimal. Finally, the
signal loss in coaxial antenna cables is greater in the UHF
range. Amplifiers and/or low-loss cable may be required in UHF antenna systems. While the regulations for users and for licensing are essentially the same in the VHF and UHF bands (FCC Part 90), regulations for the equipment allow two potential differences.

For FM signals in the UHF band, greater occupied bandwidth is allowed. This effectively permits greater FM deviation, for potentially greater audio dynamic range. In addition, greater transmitter power is allowed (up to 250 mw). Finally, the available radio spectrum for UHF wireless microphone system use is five times greater than for high-band VHF. This allows for a much larger number of systems to be operated simultaneously.

In practice, the effectively greater deviation limits of UHF are not generally used because of the resulting reduction in the number of simultaneous systems that may operated: the corresponding increased occupied bandwidth of each system uses up more of the available frequency range. Also, use of increased transmitter power is rare due to the resulting severely decreased battery life and to the increased potential of mutual system interference. Even with limited deviation and power, however, the capability for an increased number of simultaneous systems is a significant benefit in certain applications. This is especially true since UHF systems can generally be used in conjunction with VHF systems at the same location without mutual interference.

The primary economic difference between VHF and UHF operation is the relatively higher cost of UHF equipment. Typically, it is more difficult and hence more expensive to design and manufacture UHF devices. In many ways this is a consequence of the behavior of high frequency (short wavelength) radio signals. This cost differential applies to antennas, cables, and other accessories as well as to the basic transmitter and receiver. Currently, though, economies of scale have reduced this premium substantially so that it is now possible to produce basic UHF systems at prices comparable to VHF. However, advanced features and performance tend to remain in the province of high-end UHF products.