2. The VHF Band

At the beginning of the low-band VHF range is the 49 MHz region, used not only by wireless microphones but also by cordless telephones, walkie-talkies, and radio controlled toys. 54-72 MHz is occupied by VHF television channels 2- 4. The 72 MHz area is used by "assistive listening" type wireless microphone systems. 76-88 MHz is assigned to VHF television channels 5 and 6. At the top, 88-108 MHz is the commercial FM radio broadcast band. All of these regions have been used at one time or another for wireless microphone systems. Allowable deviation limits (typically up to 15 KHz) can accommodate high-fidelity audio (the same as for FM broadcast).

The propagation of these waves through the air is very good, as is
their ability to pass through many non-metallic substances (a result of their relatively long wavelength). The most attractive feature of operation in this band is low equipment cost.
Except for assistive listening systems, however, lowband VHF is not recommended for serious applications. Due to the large number of primary and secondary users, and high levels of general radio frequency (RF) "noise," this band is prone to interference from many sources. Transmitter power is limited to less than 50 mW (except in the 72-76 MHz range where up to 1 watt is allowed for assistive listening systems). Finally, the minimum proper antenna size for units in this range can be over one meter long (one quarter of a five meter wave), which can severely
limit portability and/or efficiency.

Next is the high-band VHF range, widely used for professional applications, in which quality systems are available at a variety of prices. In the US, the high-band VHF range is divided into two bands, which are available to wireless microphone users. The first of these, from 169-172 MHz, includes eight specific frequencies designated by the FCC (Part 90.263b or just "Part 90") for wireless microphone use by general business. These frequencies are often referred to as "travelling frequencies," because they can (theoretically) be used throughout the US without concern for interference from broadcast television.
Legal limits ofdeviation (+/_12 KHz) allow high quality audio transmission. Once again, power is limited to 50 mw. Propagation characteristics are good, and antenna length is more manageable at about one-half meter for a quarter-wave type.

Unfortunately, the primary users in this band include many business band and government operations such as digital paging services, forestry, hydro-electric power stations, and the Coast Guard. Since the secondary user category is not restrictive, the potential for interference from both primary and other secondary users is always present. Also, general RF noise is still fairly strong in this band. In addition, 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 travelling frequencies. Finally, these frequencies are not generally legal outside of the US and Canada.

The larger part of the high-band VHF region is 174- 216 MHz. This band is designated by the FCC for use by broadcasters and by commercial film/video producers ("Part 74"). The primary users of this band are VHF television channels 7-13.


Once again, high quality audio is possible within legal deviation limits (+15 kHz). The 50 mw power restriction is the same as for low-band, propagation losses are still minimal, and acceptable quarter-wave antenna sizes range down to less than one-half meter. The possibility of interference from other secondary users and general RF noise exists, but it is much less likely than for low-band frequencies. In addition, although this range includes powerful primary users (television channels 7-13), there are ample frequencies available (locally unused television channels) in almost any part of the US.