The basic components of wireless systems are essentially the same: the microphone, a transmitter (either built into a handheld mic or a separate “body pack” unit), and a receiver with one or more antennas. The receiver’s output is connected to the mixer.
However, a vital difference between systems is the broadcast frequency range that the system uses to transmit. Two ranges, specified and regulated by the Federal Communications Commission, exist: VHF and UHF. You’ll notice that UHF systems tend to cost more than VHF units. Here’s the difference between the two, and why one might be more applicable to your needs over the other.
VHF, or “very high frequency” is a range of radio frequencies between 49 and 216MHz. The FCC divides VHF into a low band (49-108MHz) and a high band (169-216MHz). Low-band VHF is filled with cordless telephones, walkie-talkies, radio controlled toys, television channels 2-6, and “assistive listening” wireless systems. 88-108MHz is the commercial FM radio broadcast band. In general, it’s not a good range for interference-free wireless mic use.
High-band VHF is widely used for professional applications, and includes two bands that are FCC-approved for wireless microphone users. The first of these, from 169-172 MHz, includes eight specific frequencies designated for wireless mics used by general business. These are often referred to as “traveling frequencies,” because they can (theoretically) be used throughout the US without concern for interference from broadcast television. Unfortunately, the primary users in this band include businesses and government operations such as digital paging services, forestry, hydroelectric power stations, and the Coast Guard. The potential for RFI is always present. Finally, due to the limitation of available frequency bandwidth and the spacing of the prescribed eight frequencies, it is only feasible to operate, at most, two or three units simultaneously on traveling frequencies.
The second high-band VHF region, 174-216MHz, is designated for broadcast and commercial film/video production. Primary users of this band are television channels 7-13. High quality audio is possible, transmission losses are minimal, and acceptable antenna sizes are possible. Interference from other users and general RFI exists, but it is much less likely than for low-band frequencies. In addition, there are ample frequencies available (mainly locally unused television channels) in almost any part of the US.
The UHF region also contains several bands that are available for wireless microphone systems. The primary physical characteristic of UHF radio waves is their much shorter wavelength (one-third to two-thirds of a meter). The visible proof of this is the much shorter length of antennas needed for UHF wireless microphone systems.
A consequence of the shorter UHF wavelength is reduced efficiency of transmission through the air, walls and human bodies. This can result in potentially less range for a UHF signal compared to a VHF signal. “Line-of-sight” operation is a common deciding factor when using UHF. In addition, radio wave reflections by small metal objects results in more frequent interference and dropouts. However, diversity receivers are very effective in the UHF band. Finally, the signal loss in antenna cables is greater in the UHF range. Signal amplifiers and/or low-loss cable may be required in UHF antenna systems.
On the plus side, greater bandwidth is allowed for UHF signals, permitting greater audio dynamic range. In addition, greater transmitter power is allowed (up to 250 mw). Finally, the available radio spectrum for UHF wireless system use is eight times greater than for high-band VHF. This means more systems can operate simultaneously. This is a significant benefit in complex setups and concert applications.
Typically it is more difficult and hence more expensive to design and manufacture UHF devices. However, it’s now possible to produce basic UHF systems at prices comparable to VHF. You can also run both UHF and VHF systems at the same location without mutual interference.
Does this mean that UHF is always a better choice than VHF? Not necessarily. Your needs and your budget still take precedence.
Choose UHF if:
- You travel and perform in several different cities
- You need to use more than 5 or 6 wireless systems at the same time
- You play in “crowded” radio environments, meaning there is a strong presence of other radio activity all around your location
- You’re willing and able to spend a little extra
Consider VHF if:
- You use less than 5 systems at the same time
- You perform in “open” radio environments, free from interference
- You do not have line of sight between transmitter and receiver
- Your budget is limited
Your Sweetwater Sales Engineer can help you determine which wireless system would work best in your application.