RF Glossary

50-ohm Impedance

50 ohms is the characteristic impedance of transmission lines (RG8 coaxial cabling) typically used in wireless audio to connect to transmitters, antennas, distros, receivers, etc. [see Impedance and Coaxial Cable], and the input and output impedances of the antennas and devices.  It is important to use cables of the correct impedance for RF and digital communication applications, particularly on long cable runs. 75-ohm video and cable TV coax should be avoided when connecting wireless audio devices and components.

A/B Antennas

Wireless microphone receivers typically feature two antenna inputs, labeled A and B, used for diversity reception [see Diversity]. 

Accessories for Wireless Audio

Hardware extensions of a wireless mic or in-ear monitor system deployed to increase reliability, especially as systems get larger. Examples include antenna distribution systems/distribution amplifiers, transmitter combiners, and remote antennas.

Active Antenna

A receiving antenna with an integrated RF amplifier. These antennas typically require DC power to operate [see DC Bias]. It is worth noting that boosting the received signal can also boost noise and may not deliver an improvement in reception.

Amplifier (ILAMP – In-Line AMPlifier)

An RF amplifier that is either integrated into an antenna or patched in line (external). [see Active Antennas]

Analog Wireless Audio

Wirelessly collecting microphone signals or delivering monitor signals using radio frequency transmitters and receivers. Conventional AM or FM modulation techniques are used to impress audio information onto an RF carrier at the transmitter by varying the carrier level or frequency then deriving (detecting) the audio at the receiver based on those changes.

Antenna Farm

A mildly mocking description of a grouping of often randomly placed antenna elements that mutually interfere with each other and degrade performance. An antenna farm is typified by a clutter of chassis-mounted "whip" antennas on multiple wireless audio devices sharing an equipment rack.

Antenna Gain

Antenna gain is a performance factor combining directivity and radiation efficiency. Transmission antenna gain indicates how well an antenna emits input signals as radio waves in a specific direction while receiving antenna gain describes how efficiently the antenna captures radio waves from a specific direction and converts them to electrical signals. Gain is a ratio of comparison to the performance of an idealized passive omnidirectional antenna and is typically expressed in dB.

Attenuator / Pad

A passive circuit that reduces the signal strength output of an antenna which might be overloading a device input to a lower, more acceptable level. Switchable pads can be found on the inputs of some wireless receivers. 

Band

A range of radio frequencies used for one or more specific purposes. For example, the UHF band used in North America for wireless microphones and TV broadcast falls within the range of 470 MHz to 608 MHz.

Band-pass Filter / Interference Filter

A circuit that passes signals within a certain frequency range or band with little or no attenuation but attenuates or rejects signals outside the band. RF band-pass filters are typically passive devices and placed in-line between an antenna and receiver input to reduce interference by reducing or blocking undesired out-of-band noise or signals from reaching the receiver's input.

BNC Connector

The BNC connector is a miniature quick connect/disconnect coaxial connector very commonly used on radio frequency cabling and antenna connections.

Capture Lock

When the receiver locks strongly enough onto the desired radio frequency carrier signal that it can track and ignore interfering signals.

Cascade

A serial method of sending an RF signal into a device and out of that device into another, possibly repeated with multiple devices in a "daisy chain" (as opposed to a parallel connection where a signal is split between two or more inputs simultaneously). The number of possible cascade steps is dependent on the noise floor and signal to noise ratio.

Channel

With wireless microphones, an RF channel describes one carrier frequency modulated by one microphone signal and transmitted to a single receiver. It can get a little more complicated with wireless IEMs, where the RF channel's modulation may be a mono or stereo (one or two audio channel) monitor mix being transmitted to one or more wireless IEM receivers (as with a shared monitor mix for background singers). Some wireless systems do, however, use multiple carriers – in such a system the "channel" count would be the number of wireless mics and/or IEM signals being transmitted and received.

Circular Polarization

A circularly polarized transmitting antenna emits energy in a corkscrew pattern easily received by antennas in its line-of-sight regardless of the receiving antenna’s polarity (and even an antenna with changing polarity, such as the antenna on an active performer’s IEM beltpack receiver which can change polarity with body movement). When a circularly polarized antenna is used as a receiving antenna, the polarization/orientation of the transmitting antenna is largely irrelevant. Circular polarization is commonly associated with antennas with a helical or spiral antenna element, such as the RF Venue CP Beam, though the company has also pioneered circular polarization from low profile packages with its CP Architectural and CP Stage antennas. [see Polarization]

Coaxial Cable

Coaxial electrical cable, or coax, has an inner conductor surrounded by insulating material wrapped with a concentric conducting shield and an outer protective sleeve. It is widely used for the connection of radio frequency signals between devices and antennas.

Combiner / IEM Combiner

Active transmitter combiners sum the output of multiple wireless IEM or IFB transmitters to feed a single shared antenna, resulting in lower IMD (intermod) and less potential for multipath interference at the receiver while eliminating an 'antenna farm' in the wireless IEM rack. [see IMD and Multipath].

Cross Polarization

see Polarization Diversity

DC Bias Over Coax

A DC voltage applied to a coaxial cable for remotely powering equipment such as inline amplifiers and active antennas.

Decibel (dB)

The decibel (dB) is used to express the ratio of two values of power. The output level of a transmitter compared to the measurement of the same signal at the input of a receiver could, for example, be expressed as decibel value representing the transmission loss through the air and cabling. As logarithmic values, decibels make for simpler math when comparing widely divergent values, and for calculating electronic and RF system gains and losses. dB values can also be expressed as an absolute value by use of letter code suffixes that define levels relative to a fixed reference value (e.g. dBv, dBm).

Digital Wireless

Digital wireless systems modulate RF carriers with digital audio streams. Digital modulation requires less RF bandwidth than analog modulation, allowing more channels to be operated in the same spectrum space.

Dipole Antenna

An antenna made up of two conductive elements, the length of each typically about 1/4 of the wavelength of the center frequency in the band of interest. For conventional wireless microphone systems operating in the television broadcast band, where the center frequency is around 540 MHz, each element would be about 5.5 inches long. The elements are typically fitted side-by-side horizontally or one atop the other vertically with the closet point to the array center point on each element connected to one conductor of a transmission line for feeding transmitter or receiver antenna connections. [see Half Wave Antenna].

Distributed Antenna System

When an installation requires wireless audio device coverage in multiple spaces that cannot share a line of sight to a single antenna, multiple antennas can be assigned as needed to the isolated or functional zones. For example, RF Venue's 4 ZONE active antenna combiner combines up to four separate pairs of diversity antenna connections for multi-purpose rooms, indoor-outdoor configurations, or main stages with secondary breakout rooms.

Distribution Amplifier/Distro

Wireless microphone antenna distribution amplifiers (distros) receive A/B wireless microphone signals from a pair of antennas then feed independently buffered A/B signals to multiple receivers. For any case where two or more channels are in use in a wireless microphone system, shared antennas and antenna distribution is recommended. 

Diversity

A receiving technology that ensures reliable reception by using two redundant RF chains comprising an antenna and receiver tuner. The receiver tracks the two (A/B) RF chains and selects the strongest path for demodulation. Diversity reception can be achieved in two main ways: through antenna spacing or by varying antenna polarization [see Spatial Diversity and Polarization Diversity]. 

Dropout, Hit, Signal Fade

A random, intermittent loss of clear audio in the system that occurs when the RF signal is temporarily reduced, resulting in an interruption in sound, distortion, inconsistent audio, or unwanted noises and static.

Dynamic Range

The total operating range of a device, from the weakest input signal the device can demodulate to the strongest signal it can accommodate on its input. Typically expressed in dB.

Essentials

RF Venue's complete line of wireless audio accessories with patented technologies and best-in-class performance which optimize the performance of wireless microphone or IEM systems of any brand or model. 

Frequency

Frequency is most simply how often something repeats. The number of times an electromagnetic sine wave repeats per second is expressed in Hertz (Hz). A wireless audio channel is specified by its center frequency (in MHz for UHF). 

Frequency Coordination

The practice of calculating and selecting interference-free channels for the configuration of multiple wireless audio devices. Potential sources of interference can be external (TV stations, cell phones, other wireless audio users including wireless musical instrument interfaces, etc.) and internal (when multiple transmitters are being used within a system). 

GHz

GHz stands for gigahertz, 1GHz is 1000 MHz or 1 Hz x 10⁹

Ground Plane

Ground mounted monopole antennas benefit from the earth reflecting the antenna signal. Radial conductors can be deployed at an antenna base as a "Ground Plane", an electrical approximation of the zero-potential reflective surface (earth ground). The chassis of a receiver or its internal circuit board can also serve as a ground plane for a chassis mounted antenna.

Guard Band

Relative to wireless devices operating in the television band, the “guard band” is a spectrum slice above 600 MHz (typically defined as the 614–616 MHz frequency range). The guard band has restrictive usage rules. It is intended to maximize isolation between portions of the spectrum not intended for wireless microphone use.

Half-Wave Antenna

A half-wave antenna is the most used type of dipole antenna. The combined length of its elements is approximately half of the carrier frequency wavelength (λ/2). 

Helical Antenna

See Circular Polarization

Horizontal Polarization

When the electromagnetic field emitted by a transmitting antenna travels away from an antenna on a single plane parallel to the ground, it is said to be horizontally polarized. [see Linear Polarization and Vertical Polarization]

IFB

IFB (interruptible fold back) signals, wired or more typically wireless, are used to feed instruction and cues to a host during live broadcasts.

Impedance

To ensure optimum transfer of energy between RF transmitters or receivers and the cabling and antennas they are connected to, the "impedance" of each is designed to match. Impedance is the measure (in ohms) of opposition to electrical current flow resulting from the combination of resistive and reactive elements, the latter being the conductive reaction of capacitive and inductance characteristics of a circuit or cable relative to alternating voltages. Reactive characteristics vary with source signal frequency changes while resistive characteristics are fixed regardless of signal frequency. [see 50 Ohm impedance]

In-Ear Monitor/IEM

In-Ear Monitors [IEMs] are universal or custom molded earpieces that fit in a user’s ear canal. Wireless IEM systems are used to transmit a monitor signal to a performer's IEMs or an IFB mix (interruptible fold back) to a host in a live broadcast.

IMD (Intermodulation Distortion)

Intermodulation distortion (IMD) is caused by the nonlinear mixing of multiple signals in a circuit such as the tuned inputs of wireless audio receivers and the outputs of wireless system transmitters. RF signals from wireless transmitters in close proximity can interfere with one another or introduce spurious signals into nearby receiver antennas. These signals beat together producing artifact frequencies at the sums and differences of the mixed signals. IMD artifacts can fall within the range of a wireless band in use and possibly cause interference. The more channels in a system, the more opportunity that exists for IMD issues. IMD issues can be addressed with the use of external, shared antennas.

Linear Polarization

When the electromagnetic fields emitted by a transmitting antenna travel on a single plane, the antenna is said to be linearly polarized. [see Horizontal Polarization and Vertical Polarization]

LPDA

See Paddle Antenna.

Megahertz/MHz

Hertz is the standard unit for measuring frequency and megahertz is one million hertz. UHF wireless audio gear will have an operating channel within the range of 470 to 608 MHz. (VHF band FM broadcast radio station channel frequencies –  like 92.9 or 101.5 – are also measured in MHz).

Monopole Antenna

An antenna made up of a single conductive element with a typical length around 1/4 of the wavelength of the center frequency in the band of interest. – about 5.5 inches for the television band where wireless audio systems operate. The simple "whip" antennas that chassis mount directly to wireless audio transmitters and receivers are monopole antennas. [see Quarter Wave Antenna]

Multipath Interference

In addition to the direct line-of-sight signal path between the transmitter and the receiving antenna, RF signals can reflect (or "bounce" and "echo") off objects and surfaces before they arrive at the receiving antenna. The additional reflected signals are a potential source of interference, arriving at different times in comparison to the direct signal and can reinforce or attenuate the direct signal, the level of the effect dependent on their relative phase and level. 

N-Connector

N-Type connectors are designed to satisfy the need for a durable, weatherproof, higher power capable (than BNC) RF connector with consistent performance.

Noise Floor

The sum of all unwanted RF signals at a receiver input, both man-made and naturally occurring.

Omnidirectional Antenna

An antenna, like a vertical monopole, that receives or transmits signals in 360 degree "donut" polar pattern around the element with reduced energy at the top and bottom of the antenna. 

Omnidirectional Polarity

Transmitting antennas with omnidirectional propagation emit energy perpendicularly away from the antenna element in every direction. Receiving antennas with omnidirectional reception are similarly sensitive to signal arriving from all directions.

Out of Band

RF signal above or below the band of interest. Unfiltered, out of band noise can be an interference source in receiver circuits and cause intermodulation at wireless mic/IEM frequencies.

Paddle Antenna (LPDA)

Log Periodic Dipole Array antenna. Commonly packaged as a "Sharkfin" or "Paddle", an LPDA antenna consists of three or more dipoles lined in a row to create a directional antenna. The design effectively adds front end gain or increased sensitivity to signals arriving from one direction on the same plane as the antenna elements and reduced sensitivity (or rejection) of signals from other directions.

Passive Antenna

Any antenna without active amplifier circuitry. These antennas do not need power to operate.

Passive Combiner

A passive RF device used for simple combining of two IEM transmitter signals to feed a common antenna. Typically, passive combiners reduce isolation between channels. Active combiners are needed when channel counts increase.

Passive Splitter

A passive RF device used to split one receive signal into multiple signals with some corresponding reduction in level. An example is the RF Venue 2X1SPLIT, which can split or combine an RF signal. Conversely, active distribution amps can feed an optimized signal from a shared antenna to multiple receivers. 

PoE

Power over Ethernet (PoE), where DC power is delivered along with IP or network signals using CAT cabling. PoE is commonly used on networking equipment but also on some wireless mic receivers and device extenders.

Polar Pattern

A graphical representation of measurements of a transducer's (a microphone or an antenna) input or output sensitivity strength along degrees of rotation. 

Polarity

The orientation of the waveform's voltage or current relative to a reference point or baseline. A dipole antenna's elements arranged one atop the other would have a vertical propagation polarity. With the elements side by side horizontally, the propagation polarity would be horizontal.

Polarization Cross Fade

The decrease in signal level/reception quality in a receiving antenna when its polarization does not match the polarization of the transmitting antenna.

Polarization Diversity

Polarization diversity uses a co-located pair of antennas with polarization planes oriented 90 degrees apart (i.e. a wireless mic receiver's A antenna being fed by a vertically polarized antenna and the B input being fed by a horizontally polarized antenna. Cross-polarized antennas can receive RF signals effectively regardless of their polarization angle, such as a performer rotating their wireless mic transmitter through various orientations. The patented RF Venue Diversity Fin and Diversity Architectural antennas are uniquely cross-polarized antennas built as a single unit.

Polarization Mismatch

When the polarization of a transmitted signal doesn't align with that of the receiver's antenna, the received signal strength can drop significantly.

Power

Electrical power is the rate of transfer of electrical energy within a circuit typically defined by Ohm's law. RF power is the amount of electromagnetic energy that is transmitted or received through radio waves.

Power Supply

A source of power to an electrical circuit from AC wall current conversion to DC operating voltages, or batteries. Supplies can be internal or external.

Quarter-Wave Antenna

See Monopole Antenna. The whip quarter wave antennas provided with wireless audio devices do not have a ground plane [see Ground Plane] so must be mounted directly to the chassis of the transmitter or receiver and derive an effective ground plane from the gear's chassis or circuit board.  

Rack/Rack Unit

Audio gear is commonly housed in a "rack" in a venue control room, equipment room or near operational points like FOH or a monitor consoles. The term rack can refer to the actual cabinet used to house the equipment, or it can refer to the act of mounting gear in the specialized cabinets. Equipment racks have front, and sometimes rear, vertical rails with screw holes tapped at standardized spacings. Rack-mountable gear has mounting ears with bolt holes spaced to match up with the threaded holes in the rack rails. A 1 rack unit (1RU or sometimes 1U) device will take up the entire width and height of one slot - which is approximately 1.75 inches high and 19 inches wide. Rack mount gear can be an RU height multiple such as 2RU, 3RU, 4 RU, etc. Some gear is half-rack wide, allowing two units to be mounted side by side in a full width rack adapter. 

Range

The effective operating/coverage distance of a transmitter to a receiver.

Receiver/RX

The device within a wireless system that is tuned to capture a desired RF signal and demodulate the signal’s audio content. 

Reception

The quality of signal vs. noise. Good quality means the signal is easily captured despite environmental and system noise.

Remote Antenna

An antenna that is located away from the wireless rack and closer, and/or with better line-of-sight, to the area where wireless mics/IEMs are in use.

RF Interference / RFI

Any electromagnetic signal other than your intended signal.

RF over Fiber / RFoF

A optical based system that converts a radio signal into light pulses and then back into a radio signal. Its purpose is to extend RF signals past the distance limitations of coax cables.

RG8X Coaxial Cable

RF Venue RG8X is custom-made RG8/50-ohm coaxial cabling with double-shielding to improve noise and interference rejection while maintaining very low loss.  [see Coaxial Cable] 

Signal Strength

The intensity of a specific RF signal.

Signal to Noise

The ratio of desired signal to unwanted noise in the RF spectrum. It is typically expressed logarithmically, in decibels or dBm.

SMA Connector

SMA (SubMiniature version A) are small semi-precision coaxial RF connectors used for many compact RF devices such as beltpacks. 

Spatial Diversity

Spatial diversity is a wireless technique that uses multiple antennas separated by some distance to improve signal quality and reliability by offering two possible line-of-sight paths. Typically, the spaced antennas are both vertically polarized.

Spectrum

In RF communications, the range of frequencies available for a specific purpose or group of users.

Spectrum Analyzer/SA

A measuring tool used to analyze RF energy. RF technicians, audio engineers, and AV installers use SA's to visualize RF activity in a given environment for spectrum management and troubleshooting.

Squelch

A circuit in a receiver that mutes the audio output in the absence of the desired transmitter signal.

Switch Mode Power Supply/SMPS

A compact, lightweight electronic power supply that incorporates a switching regulator for efficient AC to DC electrical power conversion.

Transmitter Combiner

Sums the outputs of IEMS/ IFB transmitters to a single antenna, resulting in lower IMD (intermod), reduce potential for multipath interference and less physical clutter in the RF rig.

Transmitter/TX

A radio frequency device that drives an antenna. A wireless microphone transmitter/TX can be built into a hand-held microphone or wireless microphone bodypack (though bodypacks typically use small external antennas). Wireless IEM transmitters are typically rack modules that transmit IEM signals to a portable IEM bodypack receiver.

Tuning

Setting transmitters and receivers for optimum transmission or capture of specific frequencies or channels.

UHF

Ultra High Frequency band. 300 MHz to 3 GHz.

Vertical Polarization

When the electromagnetic field emitted by a transmitting antenna travels away from an antenna on a single plane perpendicular to the ground, it is said to be vertically polarized. [see Linear Polarization and Horizontal Polarization]

VHF

Very High Frequency band. 30 MHz to 300 MHz.

Whip Antenna

The direct chassis mount antennas provided with wireless audio receivers and transmitters, which can also be described as quarter wave monopole (or non-dipole) antennas. They require direct transmitter or receiver connection to establish a ground plane for optimum performance. Numerous whip antennas sharing a rack are sometimes referred to as an antenna farm.

Zone

A physical area served by a dedicated antenna within a distributed antenna system. [see Distributed Antenna System]