RF Dictionary

A

Absorption	Describes the process by which RF energy penetrates a material or substance and gets converted to heat. RF energy, of the appropriate frequency, will experience severe absorption when it encounters rain.
Active	A circuit element, device or network, such as a transistor or integrated circuit, which requires a source of power other than the information signal upon which it is to act. A passive device such as a resistor, capacitor or inductor requires no external power source.
Adapter	A short, two-sided connector used to enjoin connectors from different families. It is primarily used to connect a cable (with a connector from one family) to a cable or component (with a connector from a different family).
Air interface	A general term describing any one of several techniques used to increase the signal carrying capacity of a wireless system. Examples include CDMA, TDMA, and FDMA.
Altimeter	A device that uses radar technology to determine an airplane’s altitude by reflecting an RF signal off the ground.

Amplifier	An active RF component used to increase the power of an RF signal. Amplifiers come in three varieties: high power, low noise and “other.” Other includes variable gain amplifiers and limiting amplifiers. Amplifiers are mostly solid state today, but they can also be traveling wave tubes.
Amplitude modulation	A form of modulation that works by superimposing an information signal onto an RF carrier by varying the amplitude of successive waves of the carrier.
Analog	An electrical signal that varies over time and can take on any value between its minimum and maximum values.
Antenna	An RF component used to transform an RF signal, traveling on a conductor, into an airborne wave and vice versa. For antennas to work properly, their size must be similar to that of the wavelength of the signal they are intended to radiate. Antennas can be active or passive components.
Antenna diversity	A technique that uses more than one receiving antenna to help overcome the problem of multipath.

Antenna pattern	A graphical tool used to show a birds-eye view of the RF energy radiating out from an antenna.
Attenuation	Describes the amount by which an RF signal is made smaller as it moves from one point to another. It is used interchangeably with the term insertion loss and it is measured in decibels.
Attenuator	An RF component used to make RF signals smaller by a predetermine amount, which is measured in decibels. There are two general categories of attenuators: fixed and variable. Fixed attenuators are also referred to as pads. There are two categories of variable attenuators: voltage variable attenuators and digital attenuators.

B

Balanced amplifier	An amplifier configuration that combines two amplifiers in parallel to provide redundancy and improved match.
Baluns	A passive electronic device that converts between balanced and unbalanced electrical signals. Often, they can also change impedance and can take many forms.
Bandwidth	A measure of the usable frequency range of a component of application. It equals the difference between the upper frequency and the lower frequency and can be expressed in Hertz of as a percentage.
Baseband	The lowest frequency signal in a transmitter or receiver. It is the modulated RF signal after it is fully downconverted in a receiver or before it is upconverted in a transmitter.

Basestation	The wireless access point of a cellular system. It consists of all the necessary infrastructure to enable wireless communications including a tower, antennas, cables, RF transceivers, and power supplies. It is also referred to as a cell site.
Beamwidth	An angular measure, in degrees (of a circle), used to describe the width of the RF energy radiated from an antenna. It is also a measure of the width of an antenna pattern.
Bias Tees	An example of a diplexer, used to supply DC currents (or voltage) to RF devices.
Bidirectional	Used to describe an RF component that works equally well in both direction. It can also be referred to as dual-directional. Antennas are almost always bidirectional while amplifiers are never so.

Bit error rate	A measure of the number of digital bits that are incorrectly received per million. It is a measure of a wireless link’s reliability.
Broadband	Used to describe a characteristic of an RF component or wireless application with a “wide” bandwidth. It is also referred to as wideband. A rule of thumb is that any bandwidth greater than 50% is considered broadband.
Broadcasting	An RF system in which a single transmitter is used to communicate with a multitude of geographically dispersed receivers.

C

Cable assembly	A combination of bulk coaxial cable with coaxial connectors attached to each end.
Capacitor	A small, passive component used to shape electrical signals, which is found in every electrical circuit.
Carrier	An RF signal – ideally a perfect sine wave – which has an information signal superimposed upon it, through modulation, to carry it as a wave over the air.
Cavity	Describes a family of RF components made by utilizing uniquely constructed hollow metal containers. Cavity components are primarily used for high-power applications.
Cell site	see Basestation.
Cellular	A general term used to describe any one of several mobile wireless telephony applications that divide up a given geographical area into smaller sub-regions called cells.
Channel	A frequency subdivision of a bandwidth. Most RF applications divide their allocated bandwidth into different channels.
Chipping rate	The frequency of the chips used in direct sequence spread spectrum.

Chips	A string of 1s and 0s used in direct sequence spread spectrum to spread (and de-spread) the information signal.
Circuit	An organized interconnection of passive and active electrical components to accomplish some electrical objective. A circuit can be further described as analog, digital, or RF, depending on the application.
Circulator	A three-port, passive RF device made of magnets and ferrite material that is used to control the direction of signal flow in an RF circuit.
Coaxial cable	Media used to transport an RF signal. It is comprised of an inner conductor (wire) surrounded by dielectric material (insulator) and covered by an outer conductor (shield). It is frequently referred to by its “RG” number.
Code division multiple access	A type of air interface that describes a technique of adding signal-carrying capacity to a given bandwidth by allowing multiple signals to occupy the same frequency at the same time and assigning each one the unique “address” of the intended receiver. It is also used to describe a form of direct sequence spread spectrum.
Collision avoidance	A radar system, mounted on the front of an automobile, which is used to determine the appropriate driving distance from the car in front.
Comb Generator
Combiner	A passive RF device used to add together, in equal proportion, two or more RF signals.

Component	Any object an electrical signal encounters in a circuit. Used interchangeably with the term device, all components are either active or passive.
Connector	A cylindrical, metallic object firmly attached to a cable or component that is used to facilitate joining one to the other. It is also referred to as a coaxial connector.
Continuous wave	Any RF signal that is never turned off. It is primarily used to describe a type of radar in which the transmitter is always on.
Continuous wave radar	A type of radar in which the transmitted signal is always on. See also Doppler radar.
Conversion loss	The insertion loss a signal experiences in a mixer as it goes from the RF port to the IF port or vice versa. It is measured in decibels.
Coupler	A passive RF component in which the input signal is split unevenly and the smaller one is siphoned off to be used somewhere else in the system. This type of coupler can be directional or bidirectional. There is another type of coupler called the Lange or quadrature (or quad) coupler in which the signal is split evenly between two ports, but one of the outputs is phase-shifted from the other. Quad couplers are also referred to as quad hybrids.
Current	Electrons on the move, either on a conductor or inside a component.

D

DC Block
DC Converter
Decade	A bandwidth in which the upper frequency is ten times bigger than the lower frequency.
Decibel	A mathematical conversion, utilizing logarithms of a ratio, which is used as a unit of measure for RF signals. It is primarily used to describe the (power) gain and (insertion) loss of RF components.
Demodulation	The process of separating the RF carrier from the information signal in a modulated signal.
Demodulator	An RF device used to perform demodulation. It is a complex component that is comprised of active and passive devices, especially mixers.
Detector	A passive RF component used to convert an RF power signal into a voltage signal. It is used to supply a voltage, which is proportional to the RF power signal, to another component or piece of test equipment that is not designed to handle an RF power signal.
Device	see Component.
Dielectric	Any material that does not conduct electricity (an insulator). When used in the context of RF, dielectric material is a special type of insulator that is designed to minimize the insertion loss of an RF signal being carried on a conductor attached to it.
Digital	An electrical signal that varies over time and can take on only one of two values: high and low.
Digital signal processing	Describes the process of using sophisticated mathematical computations and signal processing to pack a lot of information into a digital signal.

Diode	A semiconductor device used in many RF components. There are several different types of RF diodes that are each manufactured differently to optimize different performance parameters.
Diode Detector
Diplexer	see Duplexer
Dipole	A straight-line (omnidirectional) antenna that is one half of a wavelength long
Direct broadcast satellite	A high-power, geosynchronous orbit satellite that transmits broadcast signals to be received by small antenna dishes attached to the home.
Direct sequence spread spectrum	a form of spread spectrum in which the signal is spread by encoding it with a pseudo random number.
Directional coupler	A coupler that only works in one direction.
Discrete component	An electrical component that performs a single function and is housed in its own package.
Distributed circuit	A type of RF circuit philosophy in which some passive components are made from uniquely shaped circuit traces.
Divider	A passive RF device that equally divides an RF signal into two or more RF signals.
DLVA/SDLVA

Doppler radar	A type of radar that utilizes the return signal’s frequency shift to determine an objects velocity.
Downconverter	Another name for a mixer in a receiver, it is used to lower the frequency of the RF signal.
Downlink	The path an RF signal travels from a satellite to the ground.
Downstream	The path an RF signal travels from a basestation to the end user.
Dual directional coupler	A coupler that works equally well in both directions.
Dual mode	Describes mobile phones that can communicate in both first-generation cellular (analog) and second-generation cellular (digital) modes.
Duplex	Describes an RF system that had the ability to transmit and receive simultaneously. Used most frequently with regard to telephony.
Duplexer	A passive RF device that contains two bandpass filters with different passbands. It is also called diplexer.
Dynamic range	A measure of how large a signal an RF component can handle without distorting it. It is the key performance parameter of any device operating in a digital wireless system. One measure of a component’s dynamic range is its third order intercept point, measured in dBm. Sometimes the dynamic range is specified as a combination of a component’s third order intercept and its noise figure. The term is often used interchangeably with the term linearity.

E

Earth station

The name given to the ground facilities that communicates with a satellite.

Effective isotropic radiated power

A mathematically derived measure of the effective power leaving an antenna, whish is calculated by comparing the actual power leaving the antenna to that of an isotropic antenna. It is also used to describe the amount of RF energy from a satellite that reaches the Earth within the satellite antenna’s footprint.

Electronically scanned array

An antenna, made up of many small transceivers, that can sweep an antenna pattern without moving anything mechanically.

F

Feedback	An electrical circuit technique whereby a signal at one point in the system is sampled and “fed back” to a prior point in the system and used to make adjustments or corrections.
Ferrite	A composite material with excellent magnetic properties used to make isolators, circulators, and transformers.
Filter	A passive RF component that passes or rejects a signal solely on the basis of its frequency. There are four main categories of filters: low pass, high pass, band pass, and band reject.
Filter (cavity)
Filter (ceramic)
Fire control radar	Describes the attenuation a signal experiences as it travels away from an antenna. It is the result of the signal spreading out as it moves.

Footprint	The antenna pattern that the antenna on a satellite projects onto the Earth.
Free space loss	Describes the attenuation a signal experiences as it travels away from an antenna. It is the result of the signal spreading out as it moves.
Frequency	The measure of how many complete sine wave cycles occur in one second in an RF signal, measured in Hertz.
Frequency division duplexing	Dividing up a frequency range into two different frequency ranges for the specific purpose of accommodating a two-way conversation. Each frequency range is used solely to carry information in one direction.
Frequency division multiple access	A type of air interface that describes a technique of adding signal-carrying capacity to a given bandwidth by diving it up into smaller frequency bands.
Frequency division multiplexing	Dividing a frequency range into multiple, smaller frequency ranges, usually for the purpose of sending multiple signals.

Frequency hopping spread spectrum	A spread spectrum technique that involves constantly changing the RF carrier’s frequency in such a way that only the intended receiver can decipher it.
Frequency modulation	A form of modulation that works by superimposing an information signal onto an RF carrier by varying the frequency of successive sine waves of the carrier.
Frequency response	A graph of amplitude gain or loss, versus frequency, for an RF component. It is used to describe how the particular component behaves as the signal’s frequency changes.
Frequency reuse	Describes the unique feature of mobile wireless telephone services in which more than one party can use the same exact frequency, at the same time, in a given geographical location.

G

Gain	The increase in size of the output signal of an amplifier with respect to the input signal. It is measured in decibels.
Gallium Arsenide	A compound semiconductor material, made of Gallium and Arsenic, used to make RF diodes and transistors. It is the preferred semiconductor material choice for very high frequency RF products.

Geostationary orbit	See Geosynchronous orbit.
Geosynchronous orbit	An orbit, 22000 miles above Earth, in which satellites rotate around the Earth at the same speed as the Earth’s rotation, giving them the appearance of not moving.

Global positioning system

A system of 24 satellites that continuously transmit special signals used by special receivers to determine location.

H

Handoff

Describes the process whereby a mobile telephone call is transferred from one cell site to another with no interruption of service.

Hertz

The unit of measure for frequency, it measures a signal’s “cycles per second.”

Hybrid

When used in the context of circuit technologies, it is used to describe an RF circuit made by combining chips and discrete components onto a ceramic substrate, which is also referred to as a microwave integrated circuit (MIC). When used in the context of coupling, it describes a Lange coupler.

I

Impedance	A measure of an RF component’s input and output “size,” expressed in ohms. In RF systems, the standard size used by all components is 50 ohms.
Impedance matching	The process of converting the output impedance of some RF device – which is not 50 ohms – to 50 ohms, so that it can be operatively connected to some other component.
Impedance ratio	A number used to quantify a transformer’s ability to convert one impedance value to another. A transformer with a two-to-one impedance ratio can convert a 100 ohm impedance to 50 ohms.
Inductor	A small passive component used to shape electrical signals, which is made by winding a wire into a spiral. It is found in most electrical circuits.
Insertion loss	A measure of how much smaller the output signal of a passive device is with respect to the input signal. It is measured in decibels.

Insulator	Any material that does not conduct electricity.
Integrated circuit	Combining more than one active and/or passive device onto a single piece of semiconductor material.
Intercept point	See Third order intercept.
Interference	Any unintended or unwanted RF energy that interferes with the proper reception of the intended signal at the receiver.
Interleaving	Describes the process of alternately combining the voice information and the signal information when conducting a cellular call.

Intermediate frequency	The name of the signal between the two mixers in a two mixer receiver. It is also used to identify one of the ports of a mixer.
Interrogator	That par of a wireless RFID system that is used to detect and communicate with the transponder.
Isolation	A measure of the insertion loss in the “open” path of an RF switch, or between any two ports in a passive RF component. Like insertion loss, it is measure in decibels.
Isolator	A two-port passive RF device made of magnets and ferrite material that is used to protect other RF components from excessive signal reflection. Isolators are circulators in which the third port is connected to a heat-dissipating load.

L

Lange coupler	See Coupler.
Limiting amplifier	An amplifier that is used to protect the RF device that comes after it by limiting its output power to a predetermined level, regardless of the input power.
Linearity	See Dynamic range.

Local loop	The telephone circuit from the home (or office) to the local telephone company and back.
Local multipoint distribution service	A fixed wireless application operating around 28 GHz that is ideally suited for wireless local look service.
Local oscillator	The source of a perfect sine signal, it is connected to one of the ports of a mixer.

Loss	A measure of the decrease in size of an output signal from a passive component, with respect to the input signal. It is measured in decibels.
Lumped element circuit	A type of RF circuit philosophy that utilizes packaged passive components.

M

Macrocell	The family of cell sites with the greatest signal carrying capacity. They require relatively high power RF transmission.
Match	A measure of how perfectly two RF components “fit” together, which results in less of the RF signal between them being reflected. Match is measured by VSWR, which is expressed as a ratio X:1, and by return loss, which is measured in decibels.
Microcell	The family of cell sites that results from subdividing macrocells. They require a relatively moderate amount of transmitted RF power.
Microelectro-mechanical systems	Describes a family of integrated circuits in which a part of the circuit actually moves.
Microwave	A term loosely used to describe a range of frequencies between 1 and 40 GHz.
Microwave integrated circuit	See Hybrid

Millimeter wave	A term loosely used to describe a range of frequencies greater than 40 GHz.
Mixer	A three-port RF component used to change the frequency of one of the input signals. It is sometimes referred to as an upconverter (in a transmitter) or a downconverter (in a receiver). Mixers can be active or passive devices, although most are passive.
Mobile commerce	Also called m-commerce. Describes a set of wireless applications in which a mobile device is used to transact business.
Mobile switching center	The central communications hub of a cellular telephone system that is responsible for routing all the calls from the various basestations to other basestations, or to the public switched telephone network and for billing. It is also referred to as the mobile telephone switching office.
Mobile telephone switching office	See Mobile switching center.
Modem	A modulator and demodulator combined in a single unit

Modulation	Superimposing an information signal onto an RF carrier by varying some aspect of the carrier. There are two fundamental types of modulation: amplitude modulation and phase modulation. Frequency modulation is a subset of phase modulation.
Modulator	A device that superimposes an information signal onto an RF carrier. It has two inputs (the carrier and the information signal) and one output (the modulated signal).
Monocycle	A single, isolated sine wave.
Monolithic microwave integrated circuit	An integrated circuit designed for RF purposes. It can be made of several different semiconductor materials, but the two most common are Silicon and Gallium Arsenide.
Monopole	A straight line (omnidirectional) antenna that is one quarter of a wavelength long.
Multipath	The phenomenon in which a single wireless signal takes two different paths to the intended receiver.

N

Narrowband	Used to describe a characteristic of an RF component or wireless application with a “narrow” bandwidth. A rule of thumb is that any bandwidth less than 50% is considered narrownband.
Noise	Any unwanted changes to an RF signal. Noise usually manifests itself as unwanted changes in the sine wave’s amplitude, referred to as AM noise, although FM noise is also possible. Mixers are notorious for injecting noise onto an RF signal.

Noise figure	A measure of how much noise an RF component injects onto an RF signal. Noise figure, which is measured in decibels, is most often mentioned with regard to low noise amplifiers.
Noise sources

Notch filter

Also called a band reject filter, it allows all frequencies to pass except those in a narrowly defined frequency range.

O

Octave	Describes a bandwidth in which the upper frequency is twice as big as the lower frequency.
OCXO

Omnidirectional

Describes an antenna that radiates RF energy out equally in all directions.

Oscillator

An active RF component with a sole purpose to produce a perfect sine wave at a predetermined frequency. It is also referred to as a source.

P

Pad	A fixed attenuator (its insertion loss is constant).
Passband	The frequency range of a bandpass filter that has low insertion loss and therefore allows the signal to pass. A passband is defined by identifying its upper and lower frequency.
Personal area network	A form of local area network in which a human being, carrying a mobile wireless device, acts as the access point of the network.
Personal communication services	Second generation (digital) cellular services in the United States.
Phase locked loop	An oscillator that incorporates feedback in an effort to produce a more perfect sine wave. A phase locked look can be part of a very sophisticated oscillator called a synthesizer.
Phase modulation	A form of modulation that works by superimposing an information signal onto an RF carrier by varying the phase of successive sine waves of the carrier. This modulation has a similar effect to frequency modulation.

Phase shifter
Picket generator
Picocell	The smallest family of cell sites. They provide for the least signal carrying capacity, cover the smallest area, and require the lowest amount of transmitted RF power.
Piconet	A wireless network using the Bluetooth protocol, which contains up to eight nodes.
Polarization	Refers to the fact that RF sine waves have spatial orientation to them as they travel in the air. The three types of polarization are horizontal, vertical, and circular.
Power combiner

Power density	A measure of the RF energy in the air that passes through a given area and has the unit of watts per square meter.
Power divider	See Divider.
Power supplies
Printed circuit board	Describes a circuit technology in which metal traces are mounted on a plastic composite material that is used to interconnect electrical components. The motherboard inside a personal computer uses a printed circuit board.
Propagation delay	The time it takes for a signal to travel from the Earth to a satellite and back again. For satellites in geosynchronous orbit, the delay is about a quarter of a second.
Pseudo random noise	A digital bit stream that appears random (when viewed on a spectrum analyzer), but in reality repeats itself over some long period of time.

Q

Quadrature (Quad) coupler

See Coupler

Quadrature (Quad) hybrid

See Coupler

R

Radar	A wireless system that uses reflected RF energy to detect an object’s range, location, and velocity.
Radar cross section	The effective area to reflect RF energy of an object being sensed by radar.
Radiate	A term used to describe the process by which an RF signal changes into an airborne wave.
Radio frequency	Used to identify a class of high frequency electrical signals intended to be radiated as waves. It is also used to describe a range of frequencies less than 1 GHz.

Radome	A hard protective shell that covers an antenna and protects it from the elements while letting the RF pass through it.
Receiver	One of the two main building blocks of a wireless system that is responsible for collecting the RF energy from the antenna and reducing the signal’s frequency down to where it can be accepted by the demodulator.
Reflection	A term used to describe an RF signal’s behavior when it encounters an impedance mismatch or a solid object. With an impedance mismatch, some (or all) of the RF energy is reflected back in the direction from which it came. With a solid object, the RF energy bounces off the object at the same angle at which it encountered it.
Repeater	A general term used to describe an RF system that is designed to geographically extend the RF coverage of a macrocell.

Resistor	A small, passive component used to reduce the size of electrical signals that is found in every electrical circuit.
Return loss	A measure of match between two RF components, expressed in decibels. The better the match – the less energy reflected – the higher the return loss.

S

Saturation	The behavior of all amplifiers when the input power exceeds a certain point, the amplifier no longer amplifies, and the output is more or less constant. When an amplifier is in the saturated region, it is said to be non-linear and it causes distortion to the RF signal.
Scanning	Electrically or mechanically moving a radar’s antenna pattern to achieve radar coverage over a large area.
Self-resonate frequency	The frequency at which an object will oscillate if sufficiently excited by electrical energy. Almost all solid objects have a self-resonate frequency.
Signal	Electrical energy that is made to vary, over time, in a controlled manner.
Silicon	A semiconductor material used to make RF diodes and transistors. Because it is low cost, it is the preferred material choice for low-frequency RF products.
Simplex	Describes an RF system that can only transmit in one direction at a time.
Skin effect	A term used to describe an RF signal’s behavior when it is on a conductor. Because of their high frequency, RF signals do not penetrate into a solid conductor, but rather exist exclusively on the outer surface.

Source	See Oscillator.
Specialized mobile radio	A cellular-like service in the United States that combines standard cellular operation with dispatch capability.
Spectral efficiency	A measure of the data-carrying capacity of a wireless system, which has the units of bits per second per Hertz.
Spectrum	A term used to describe a range of frequencies for a specific application.
Spectrum analyzer	A tool used by RF engineers to visualize the RF energy over some range of frequencies. It is a plot with the horizontal axis in units of frequency and the vertical axis in units of power.
Spread spectrum	A digital modulation scheme that increases the signal carrying capacity of a given bandwidth by allowing multiple signals to occupy the same frequency and distinguishing each one by its unique “address.”
Station keeping	The practice, by satellites, of using small bursts of propellant to change position to ensure that they do not stray very far from their intended location in geosynchronous orbit.

Stopband	The frequency range of a band reject filter that has high insertion loss and therefore stops signals from passing. A stopband is defined by identifying its upper and lower frequency.
Subassembly	See Subsystem.
Subsystem	An RF item, in a single container, that performs more than one function and utilizes more than one component. For example, a combination of a mixer, a filter, and an amplifier in a single box is considered a subsystem.
Surface acoustic wave	An electrical signal converted to a sound wave. In surface acoustic wave devices, the sound wave travels along the surface of the device, rather than inside of it.
Switch	An active RF component that switches a single input between one or more outputs. RF switches are characterized by their number of poles (switches) and throws (outputs).
Synthesizer	A very sophisticated oscillator incorporating other electronic circuitry, plus feedback, to make a more perfect sine wave.

T

T/R switch	A single-pole, double throw switch situated between a transmitter, a receiver, and an antenna.
Termination
Thermal impedance	A measure of how hot a component gets for a given amount of power dissipated. It is expressed in C/Watt.
Third order intercept	The measure of an RF component’s linearity or dynamic range, expressed in dBm. It is also referred to as the intercept point. The higher the measure, the more linear the component and the less distortion of the RF signal.
Time division duplexing	Dividing up a single communication channel into multiple time slots for the specific purpose of accommodating a two-way conversation. Alternating time slots are used for alternating directions.
Time division multiple access	A type of air interface that describes a technique of adding signal-carrying capacity by breaking up each frequency allocation into multiple time slots and assigning each signal a specific slot.
Trace	A small, thin piece of metal on a dielectric material used to carry signals.

Transceiver	A combination transmitter and receiver in a single package.
Transfer curve	A graph of output power versus input power of an amplifier.
Transformer	A passive RF component used in impedance matching, among other things. It is defined by its impedance ratio.
Transistor	A semiconductor device utilized primarily in amplifiers to create gain, they can also be used by other RF components to perform switching. There are many different varieties of transistors that are made from different semiconductor materials.
Transmitter	One of the two main building blocks in a wireless system that is responsible for taking the signal from the modulator, increasing its frequency and power, then radiating it out the antenna.
Transponder	An RF subsystem on board a satellite that is responsible for receiving the uplink signal, converting it to the downlink frequency, and then re-transmitting it. It is also the name given to that part of a wireless RFID system that gets detected by the interrogator.
Traveling wave tube	An older technology RF amplifier that amplifies RF signals in a vacuum inside a cavity.

Triangulation	A method for determining position by receiving three different wireless signals from three different locations
Trimmer
Triplexer	A passive RF device that contains three bandpass filters with different passbands.
Tuner	An RF device, used in a receiver, to frequency select individual channels.
TXCO

U

Upconverter

Another name for a mixer used in a transmitter, which is used to raise the frequency of the RF signal.

Uplink

The path an RF signal travels from the ground to a satellite.

Upstream

The path an RF signal travels from the end user to the basestation.

V

Varactor	A diode used to vary the frequency in a voltage controlled oscillator.
Variable gain amplifier	An amplifier with an external control that is used to vary its gain.

Very small aperture terminal	An RF system in which many small Earth stations use a satellite to communicate with a single receiver.
Voltage	Electrical potential. There are two types: AC (alternating), like the kind in a wall outlet, and DC (direct), like the kind in a battery.

Voltage controlled oscillator	An oscillator with an external control that is used to vary its output frequency.
Voltage standing wave ratio	A measure of match between two RF components, expressed as a ratio of X:1. The lower the X, the better the match.

W

Watts	Unit of measure for any kind of power, e.g., RF, heat, etc.
Waveguide	Pipes, with rectangular cross sections, used to carry RF signals from one point to another. Inside, the RF signals move as waves and the waveguide serves to guide and control their movement.
Wavelength	A measure of the length of an RF signal. The higher a signal’s frequency, the shorter its wavelength.

Wideband	See Broadband.
Wireless	A marketing term generally used to describe the newer RF applications.
Wireless local area networks	A local area network of computers that communicate via wireless signals.

Wireless local loop

An RF system that allows communication with the local telephone company, wirelessly.