Glossary

NI RF Vector Signal Analyzers (NI-RFSA 18.1) Help

Edition Date: June 2018

Part Number: 372058U-01

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Prefixes

Symbol Prefix Value
p pico 10 -12
n nano 10 -9
µ micro 10 -6
m milli 10 -3
k kilo 10 3
M mega 10 6
G giga 10 9
T tera 10 12

Numbers/Symbols

nV nanovolts 10-9 volts
µV microvolts 10-6 volts
µΩ microohms 10-6 ohms
mΩ milliohms 10-3 ohms
MΩ megaohms 106 ohms
pA picoamps 10-12 amperes
nA nanoamps 10-9 amperes
µA microamps 10-6 amperes
mA milliamps 10-3 amperes

A

active configuration list A configuration list that has been enabled.
active step A step that is part of the active configuration list. The active step specifies what is currently being configured.
ADC analog-to-digital converter—A hardware component that converts analog voltages to digitized values. An ADC can convert an analog signal to a digital signal representing equivalent information.
ADE application development environment—A software environment incorporating the development, debug, and analysis tools for software development. LabVIEW, Measurement Studio, and Visual Studio are examples.
AM amplitude modulation—The process that varies the amplitude of an RF carrier wave according to the amplitude of the message signal.

API application programming interface—Programming interface for controlling some software packages, such as the instrument design libraries.
ASK amplitude-shift keying—Refers to a type of amplitude modulation that assigns bit values to discrete amplitude levels. The carrier signal is then modulated among the members of a set of discrete values to transmit information.

B

baseband signal The baseband is the range in the frequency spectrum occupied by the unmodulated message signal. Both the message signal and the downconverted complex I/Q signal are referred to as baseband signals.
burst noise Electronic noise that occurs in semiconductors. Burst noise consists of sudden step-like transitions between two or more discrete voltage or current levels, as high as several hundred microvolts, at random and unpredictable times.

C

carrier The signal that carries the information encoded or modulated on it. Typically, the carrier is a fixed frequency sine wave, which can be amplitude, phase, or frequency modulated. In advanced forms of telecommunication systems, the carrier may be a moving signal, called a spread spectrum. As long as the characteristics of the carrier signal are deterministic and known by the receiver, virtually any type of carrier signal can be used.
center frequency The middle frequency of the channel bandwidth. In frequency modulation, the center frequency is equal to the rest frequency—specifically, the frequency of the unmodulated carrier wave.
closed-loop RF list mode case A scenario in which the RF device and the device under test exchange signals along trigger lines to advance through the configuration list. Generally, the closed-loop case assumes that the RF device uses external signals, namely triggers, to advance through the frequency list and that the RF device can produce events as it moves to each step in the RF configuration list.
configuration list A list of operations for the RF vector signal analyzer.

D

dBFS Decibels relative to full scale—a measure of decibel amplitude level in a digital system that has a defined maximum available peak level.
DDC digital downconverter—A hardware component that performs IF to I/Q conversion in the digital domain. The DDC frequency-translates RF signals to center around a specified IF frequency, while filtering certain frequency bands and reducing the signal sampling rate.
demodulation Describes the recovery, from a modulated wave, of a signal having the same characteristics as the original message signal.
DSP digital signal processing
DUT device under test
dynamic range The range between the minimum detectable signal, typically the noise floor, and the -1 dB compression point.

E

endpoint See peer-to-peer endpoint.
external digitizer mode Programming mode in which you specify a non-National Instruments digitizer for use with your NI RF hardware modules.

F

fetch Process that transfers data from device onboard memory to PC memory.
FFT fast Fourier transform—An efficient mathematical algorithm used for spectrum analysis. Refer to Fourier transform.
flicker noise Predominantly a low-frequency phenomenon because the power spectral density varies as 1/f. This type of noise is present in all conductors and semiconductors becomes important in IC devices because of manufacturing defects. Also known as pink noise.
FM frequency modulation—A process that varies the frequency of a sinusoidal carrier wave from a center frequency by an amount proportional to the instantaneous value of the message signal. In FM, the center frequency is the carrier frequency.

Fourier transform A mathematical technique that resolves a given signal into the sum of sines and cosines. Widely used as the FFT (fast Fourier transform), which is the basis for spectrum analysis.
frequency The number of cycles per unit time. The International System of Units has set hertz (Hz) as the standard unit of measurement for frequency, where 1 Hz equals one cycle per second.
FSK frequency-shift keying—A type of frequency modulation which assigns bit values to discrete frequency levels.

G

gain Amplification of a signal. A gain of two corresponds to a doubling of the signal level.

H

harmonic In a complex signal, a component with a frequency that is a multiple of the fundamental frequency.
HDDR harmonic distortion dynamic range—The minimum distortion an instrument can measure, about –96 dBc/Hz for the NI 5661 RF vector signal analyzer.

I

IF intermediate frequency—The intermediate signal that an RF signal is converted down to in order to be digitized, demodulated, displayed, or processed. For instance, the PXI-5600 RF downconverter module converts RF signals to IF signals in a band between 5 to 25 MHz.
I/Q data The translation of the magnitude and phase data of a signal from a polar coordinate system to a complex Cartesian (X,Y) coordinate system.

L

linearity For signal measurement systems, linearity refers to mechanical response of hardware to signals. A linear system will respond in a determinable way to signals. A nonlinear system contains components that do not respond to signals in a determinable way for a variety of reasons that include, but are not limited to: temperature susceptibility, improperly terminated connections, and inherent device design. This nonlinear response to signals contributes noise to a system. If a system is nonlinear, the system's response to signals will produce noisy results.
LO local oscillator

M

message signal Contains the data for transmission. The message signal is used to modulate the carrier wave to create the modulated wave for transmission. The message signal data is recovered from the modulated wave by a process of demodulation. The message signal is often referred to as the baseband signal or the information signal.
MIMO multiple input, multiple output—A measurement technique, most often used in acoustics and vibration, to identify signal paths and frequency response functions from multiple inputs to multiple outputs. Associated with this measurement class are the techniques of partial and multiple coherence, which help identify which parts of an output signal are due to a specific input signal or combinations of signals.
mixer A nonlinear analog circuit that multiplies two signals. Mixers are typically used to shift signal frequencies. A mixer receives two sinusoidal input signals at different frequencies and returns a signal with components at frequencies equal to the sum and difference of the two original input frequencies. Nonlinear mixers are used when performing amplitude modulation of RF carrier signals.
mixer level Represents the attenuation to apply to the input RF signal as it reaches the first mixer in the signal chain.
modulated wave Refers to the signal for transmission, and consists of the carrier wave modulated by the information signal. The information signal is recovered by the receiver through a process of demodulation.
modulation A process, or the result of a process, by which characteristics of a carrier wave are altered according to information in the baseband signal to generate a modulated wave that is transmitted.
MXI Multisystem Extension Interface—A high-speed serial interface bus designed to connect computers to PXI or to connect multiple PXI chassis. In this document, MXI refers to NI MXI-3 or MXI-4 systems.

N

NI-P2P An API for creating peer-to-peer streaming operations with your National Instruments hardware.
noise figure An expression of the noise generated within a device, specified in dB, above the theoretical noise floor of a given bandwidth. Thus, a device with a noise figure of 0 dB has achieved the theoretically lowest noise. The noise figure of a unit under test (UUT) is the ratio of its noise power to the noise power that a matched resistive load would deliver at room temperature.
Nyquist frequency When an analog signal is sampled at a rate more than twice that of its highest frequency component, it can be properly reconstructed when reconverted back to the analog domain. The required sampling rate is called the Nyquist frequency.

O

OCXO oven-controlled crystal oscillator
open-loop RF list mode case A scenario in which the RF device advances through the RF configuration list based on a user-defined time-specification for each step.

P

passband The range of frequencies which a device can properly propagate or measure.
passband flatness A measure of the amplitude accuracy of the frequency response with respect to frequency. Passband flatness is typically specified in ±dB and referenced to the amplitude of the frequency response at a designated frequency.
PCI Express peripheral component interconnect express— A version of PCI that maintains the PCI software usage model and replaces the physical bus with a high-speed serial bus serving multiple lanes.
peer-to-peer endpoint Each user device that is connected to a peer-to-peer system is an endpoint. An endpoint can be an RF device, PC, laptop, or other device.
peer-to-peer stream The flow of data in a peer-to-peer system. The peer-to-peer stream acts like a single, unidirectional pipe from which data can flow directly from one device to another.
peer-to-peer streaming A data streaming architecture used to transfer data between hardware devices. Use of this architecture allows two or more devices to transfer data directly to each other without first going through the host processor.
PFI Programmable Function Interface—I/O channels to the digital waveform generator/analyzer. Functionality and specifications will vary by device and operation.
PLL phase-locked loop—An electronic circuit that controls an oscillator so that the circuit maintains a constant phase angle relative to a reference signal.
PM phase modulation—process that varies the phase angle of a carrier wave from its reference value by an amount proportional to the instantaneous value of the modulating message signal. The resulting phase-modulated wave is transmitted.

preselector A YIG-tuned filter that filters unwanted frequency components from the RF input before the signal reaches the first mixer in the NI 5665 (14 GHz).
PSK phase-shift keying—In a digital transmission, refers to a type of modulation where the phase of the carrier is discretely varied either in relation to a reference phase or to the phase of the immediately preceding signal element.
PXI PCI eXtensions for Instrumentation—Rugged, open system for modular instrumentation based on CompactPCI, with special mechanical, electrical, and software features.
PXI Express (PXIe) PCI Express eXtensions for Instrumentation—The PXI implementation of PCI Express, a scalable full-simplex serial bus standard that operates at 2.5 Gbps and offers both asynchronous and isochronous data transfers.
PXI trigger bus PXI equivalent of the RTSI bus, with additional timing and synchronization capabilities.

Q

QAM quadrature-amplitude modulation—A form of quadrature modulation in which the two carriers are both amplitude-modulated.
QPSK quadrature-phase shift keying—A form of phase-shift keying in which four different phase angles are used. In QPSK, the four angles are usually separated by 90° spacing.
quadrature modulation Any modulation scheme that uses two carrier waves out of phase by 90° that are modulated by separate information signals.
quantization effects A general term that refers to either noise or distortion introduced when a signal is digitized. The nature of the quantization effects depends on the timing relationship between the input signal and the sampling system timing.
quantization noise Noise introduced when a signal is digitized, a kind of quantization effect. Digitized signals always contain quantization noise because the resolution of the ADC is finite.

R

RBW resolution bandwidth—Determines the FFT bin size or the smallest frequency that can be resolved.
reader handle A reader handle specifies the resource from which the peer-to-peer stream originates. A reader handle is configured for each destination endpoint in a peer-to-peer stream.
record A group of samples. Acquired data is stored into device onboard memory as a record. When configuring an acquisition session, you can determine how many samples are stored in a record.
Reference Clock Clock to which a device phase locks another, usually faster, clock. A common source for the Reference Clock is the 10 MHz oscillator present on the PXI backplane.
reference frequency Specifies the Reference Clock frequency, in hertz (Hz), when the Ref Clock Source property is set to ClkIn or RefIn, or when the NIRFSA_ATTR_REF_CLOCK_SOURCE attribute is set to NIRFSA_VAL_CLK_IN_STR or NIRFSA_VAL_REF_IN_STR.
reference level The reference level represents the maximum expected power of an input RF signal.
resolution The smallest signal increment that can be detected by a measurement system. Resolution can be expressed in bits, in proportions, or in percent of full scale. For example, a system has 12-bit resolution, one part in 4,096 resolution, and 0.0244 percent of full scale.
RF configuration Refers to the parameters of an RF device. The configuration determines how the RF vector signal analyzer operates.
RF configuration list A list of steps that determines the RF configuration while using the RF list mode feature. Each RF configuration list step sets the state of the instrument by specifying values for particular attributes or properties.
RF list mode An operating mode in which the device deterministically steps through a predetermined set of RF configurations as specified by an RF configuration list.
rms root–mean–square—The square root of the average value of the square of the instantaneous signal amplitude; a measure of signal amplitude. The rms voltage of a signal is computed by squaring the instantaneous voltage, integrating over the desired time, and taking the square root.

S

Sample Clock Signals that are used to clock samples in or out of ADCs and DACs. Samples are generated or acquired based on Sample Clock cycles.
sample rate The rate at which a device acquires an analog signal, expressed in samples per second (S/s). The sample rate is typically the clock speed of the analog-to-digital converter (ADC).
sFDR spurious free dynamic range—The separation or distance, expressed in dB, from the amplitude of the fundamental frequency and the next highest spur.
shot noise Shot noise is a consequence of current flowing across some sort of barrier. Also called Schottky noise.
signal bandwidth Twice the maximum baseband signal deviation from 0 Hz. Usually, the baseband signal center frequency is 0 Hz. In such cases, the signal bandwidth is simply the baseband signal's minimum frequency subtracted from its maximum frequency, or fmax – fmin.
signal chain The path an incoming signal takes through the components of a device.
sinusoid A mathematical function that describes a repetitive oscillation. Sinusoid is synonymous with sine wave.
SMA A small type of threaded coaxial signal connector typically used in higher frequency applications.
SMB sub-miniature type B—A small coaxial signal connector typically used in high-frequency applications. SMC uses a threaded connector, while the SMB "snaps" to the mating connector.
SMC sub-miniature type C—A small coaxial signal connector typically used in high-frequency applications. SMC uses a threaded connector, while the SMB "snaps" to the mating connector.
span Typically refers to a range of frequencies, for example from 10 kHz to 20 kHz. This term often describes the range that an instrument, such as a spectrum analyzer, is set to measure, or the range over which a set of frequencies of interest are located. For example, an FM modulated signal may cover a span from 100.5 MHz to 101.5 MHz.
spectrum The complete distribution of electromagnetic radiation, with bands classified according to frequency or wavelength. In respect to radio frequency, the RF spectrum pertains to the electromagnetic frequencies that are used for communications, including radio, television, radar, and microwaves. RF wavelengths are in the range of 100 km to 1 mm; and frequencies in the range of 3 kHz to 300 GHz.
spurs spurious effects—Undesired signals. Spurious signals can be considered in two classes: 1) Stationary, that is, their frequency and amplitude do not change significantly, 2) Non-stationary, where the frequency and/or amplitude change significantly over short time periods.
superheterodyne Refers to the use of at least two mixers (in sequence) in a receiver signal chain. Also implies the use of at least one intermediate frequency (IF) signal chain within the receiver. A signal detector can be counted as the final mixer.

T

THD total harmonic distortion—The ratio of the sum of the powers of the first five harmonics above the measured fundamental frequency to the power of the fundamental frequency. THD is usually expressed in dB or dBc. Measurements for calculating the THD are made at the output of a device under specified conditions.
thermal noise Noise caused by the random motion of particles at any temperature above absolute zero Kelvin.
Timer Event An event based on time intervals. The Timer Event is the source for digital edge Advance trigger. The Timer Event, in essence, allows the RF configuration list to advance.
transient A brief oscillation resulting from a sudden change of voltage, current, or load.
trigger Any event that causes, starts, or stops some form of data capture. An external stimulus that initiates one or more instrument functions. Trigger stimuli include a front panel button, an external input voltage pulse, or a bus trigger command. The trigger may also be derived from attributes of the actual signal to be acquired, such as the level and slope of the signal.
TTL Transistor-Transistor Logic

U

UUT unit under test

V

VCO voltage-controlled oscillator
VSA vector signal analyzer
VSG vector signal generator
VST vector signal transceiver
VSWR voltage standing wave ratio—The loss due to the mismatch introduced into the signal by the load or source signal path characteristics. The ratio of the highest voltage to the lowest voltage found in the signal.

W

writer handle A writer handle specifies the resource at which the peer-to-peer stream ends. A writer handle is configured for each destination endpoint in a peer-to-peer stream.

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