Specifications

between UHF and VHF wireless microphones. Due to their more complex

design and circuitry, however, UHF systems are typically more expensive

than comparable VHF systems. It should be noted that UHF and high-band

VHF frequencies are reserved by the FCC for use in broadcast and film/video

production, but it is the responsibility of the purchaser to observe FCC rules

regarding their use. Regulations regarding authorized use of these

frequencies have not been strongly enforced in the past, however, with the

result that it is not unusual to find professional frequencies being used by

unauthorized users.

Once you’ve narrowed down the list of possible frequencies to use, you

need to decide which of the two types of receivers you need: single antenna

or diversity. The first type utilizes a single antenna mounted on the back of

the receiver. The RF signal from the transmitter’s antenna radiates in all

directions, and gets reflected off large surfaces like walls and ceilings. The

reflected signal can add to or subtract from the direct signal, sometimes

resulting in a net signal strength of zero at the receiving antenna’s position.

This condition, known as multipath interference

, may come and go rapidly

as the person carrying the transmitter moves around the room, causing the

RF signal to be interrupted for a fraction of a second. This is called a

dropout

. Depending on the duration and severity of the dropout, you may

hear a quick “pfft” sound, a brief buzz or crackle, or a complete loss of audio.

Diversity receivers do a better job of resisting signal interruptions. They utilize

two antennas — mounted a short distance from each other — and a “smart” circuit

that selects the better of the two signals at any given moment. Diversity receivers

provide a noticeable improvement in audio quality, since it is unlikely that the signal

to both antennas will be interrupted at the same instant.

Portable battery-powered wireless receivers are available for use in situations

where both the transmitter and the receiver must move around. These units are

very small — usually about the size of a cigarette pack — and can be worn on the

Non-diversity and diversity explanation