Glossary

AM: Amplitude Modulated (carrier level shifts)

BANDWIDTH : The amount of frequency allocated for an RF transmission. For VHF radio mikes the FCC permits 15 kHz deviation or bandwidth. In practice, this means that a frequency-modulated signal will vary 15 kHz on either side of its carrier frequency. A radio mike operating at 169.925 mHz will actually use bandwidth from 169.910~169.940 mHz. The bandwidth is the "real estate" of the signal and is directly related to the quality of the transmission. It is roughly analogous to the size of the negative in photography; large format usually yields superior results but the excellance of design and manufacture are also important factors. In UHF the FCC permits 75 kHz deviation, making UHF radios "wide-band" compared to VHF.

CARRIER: The operating frequency of a wireless system. A fixed frequency radio signal which is shifted up and down (modulated) in either frequency (FM) or level (AM) by the audio signal.

COMPANDOR : A combination of a compressor at the transmitter to reduce the dynamic range of the transmitted signal and an expander at the receiver to recover this signal to the original dynamic range. The transmitter encodes (compresses) the dynamics of the audio signal and the receiver decodes (expands) the dynamics of the audio signal. Used in communications systems to improve signal-to-noise as a result of reduced transmitted dynamic range.

DIVERSITY: A method of reducing or eliminating multi-path dropouts by using two or more antennas and/or receivers. By definition, a receiver connected to two antennas with a splitter is a diversity receiver but that is not an effective system. In practice, diversity systems are usually one of two designs. In the dual-antenna phase switching design a circuit switches back and forth between two antennas, choosing the stronger signal and routing it to the audio circuitry of the receiver.
In "true diversity" systems there are two complete receivers and a circuit switches back and forth between the cleaner audio. In either system, best results are achieved when the antennas are placed at least one wavelength apart.

DROP OUT: A momentary loss of the carrier and sound, or a buildup of background noise.

FCC - Federal Communications Commission. The government agency responsible for regulating telecommunications in the United States, located in Washington, D.C. Their responsibilities for public radio communications, such as cellular, include allocation of frequencies, the development of regulations that govern their use and monitoring to ensure that regulations are followed.

FM: Frequency Modulated (carrier frequency shifts) The commonly used radio mike systems are all FM.

FREQUENCY AGILE: A design permitting user selection of a variety of carrier frequencies. The advantage is that if one frequency has interference from another source, one can select others which may be clear. The broader the spectrum of frequency agility, the greater the liklihood one can find clear air.

HDTV: High definition television. Standard broadcast TV is assigned a channel spanning 6 mHz but will usually use somewhat less than the full bandwidth in its transmission. HDTV, on the other hand, used the entire 6 mHz bandwidth.

MULTICOUPLER: An amplifier to boost signal strength from an antenna, permitting several radio receivers to be connected to the same antenna.

MULTI-PATH: The presence of multiple signals arriving at the receiver antenna simultaneously. Signals that are in phase will add to one another. Signals that are out of phase will cancel one another.

RF NOISE: Radio signals generated by something other than the transmitter. Usually sounds like hiss, static or hash. RFI (Radio Frequency Interference) may be AM or FM, but the effect is that it either alters the audio signal, or adds background noise to the audio signal.

RF: Radio Frequency. Also used generally to refer to the radio signal generated by the system transmitter, or to energy present from other sources that may be picked up by a wireless receiver.

RFI: Radio Frequency Interference. A non-desired radio signal which creates noise or dropouts in the wireless system or noise in a sound system. RFI can be generated by a wide variety of sources including electronic organs, computers, switching power supplies, broadcast radio signals and outside radio devices. Radio signal energy can enter a sound system component or alter the audio signals in cabling, producing annoying hiss, whining or intelligible audio signals. Among the most common sources of interference in film production are: neon lights (especially the balasts), florescent lights and balasts, lights on dimmers, automobiles with poorly shielded ignitions, the take-up motors on some cameras, power transformers, radar when working at military installations, on-set walkie-talkies especially when "cued," any electric motor and, sometimes, the other radio mikes being used by crews from various entertainment shows covering the shoot.

SQUELCH: A muted, or silent, condition in the receiver. When the radio signal from a transmitter is too weak to produce a quality audio signal, the receiver will shut off or "squelch." "Squelch" is also used to refer to the circuit in the receiver that provides the audio muting. Typically this works with a high frequency "pilot" tone, usually about 30 kHz which is mixed in with the audio. If the pilot signal is weak or not present, audio is supressed.

TRAVELING FREQUENCIES: A narrow band of VHF frequencies which were not assigned to any television broadcast and could be used throughout the United States with less risk of interference. Note that this applies only to the United States.

UHF - Ultra High Frequency (generally 300 MHz to 3000 Mhz).

VHF - Very High Frequency (30 to 300 Mhz). High Band wireless systems are usually 150 MHz to 216 MHzLow band wireless systems are usually 30 MHz to 50 MHz.