Wireless microphone

There are many standards and frequencies in wireless microphones. They can transmit, for example, in radiowaves UHF, VHF, FM, AM, and some cheap models, in infrared light. The infrared microphones have the disadvantage that they require a line of sight between the microphone and the receiver, while more expensive radio frequency models don't.

Some models operate on a single fixed frequency, and the most advanced models are capable to operate under a user selectable frequency to avoid interference and allow the use of several microphones at the same time.

Generally they are 2 types of wireless microphones: handheld and bodypack:

• Handheld is like a normal microphone, but it has a bigger body to accomodate the transmitter and battery pack.
• Bodypack is a small box housing the transmiter and battery pack, but not the microphone itself. It is attachable to belt or somewhere else and has a wire going to headset or lavalier microphone.

Advantages and disadvantages

The advantages are:

• The freedom of movement it gives to the artist or speaker.
• It avoids cabling problems that are very common on wired microphones, caused by constant moving and stressing the cables.

The disadvantages are:

• Inferior sound quality compared to wired microphones
• Sometimes limited range (a wired balanced XLR microphone can run up to 300 ft or 100 meters)
• Possible interference with other radio equiment or other microphones
• Limited number of operating microphones at the same time and place
• Limited operation time (they are battery operated)
• Noise or dead spots (places where it doesn't work, in non-diversity systems)

Techniques

The professional models transmit in radio frequency and have diversity reception (2 antennas), which eliminates dead spots (caused by phase cancellation) and the effects caused by the reflection of the radiowaves on walls and surfaces in general. (See antenna diversity).

Another technique used to improve the sound quality (actually, to improve the dynamic range), is companding.

Some models have adjustable gain on the microphone itself, to be able to accommodate different level sources, such as loud instruments or quiet voices. The ability to adjust gain helps avoiding clipping.

Some models have adjustable squelch, which silences the output when the receiver does not get a strong enough (or good enough) signal from the microphone instead of reproducing noise. When squelch is adjusted, the threshold of the signal quality or level is adjusted.

Technologies

UHF

UHF transmission frequencies

Channel	Frequency
U1	801.375 MHz
U2	801.875 MHz
U3	803.125 MHz
U4	803.750 MHz
U5	804.500 MHz
U6	805.750 MHz

External links

• WIRELESS MICROPHONES AND THE AUDIO PROFESSIONAL