Note: Send additions and/or corrections to Terry Romero tromero@nrao.edu .

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GLOSSARY

 

 

 

Additional Sources: http://www.webopedia.com/

http://www.acronymfinder.com/

http://www.atis.org/tg2k/

http://www.m-w.com/

http://www.nrao.edu/e2e/documents/e2eglossary.html

 

10 Base T - - 10 Mbps Ethernet

 

100 Base T - - 100 Mbps Fast Ethernet

 

10/100 Base T - - auto select between 10 Base T and 100 Base T

 

1dB compression point - - signal level at which a nominally linear RF device=s gain is degraded by 1db due to compression

 

4-band - - see frequency bands

 

A/D - - (also ADC) analog to digital conversion

A-rack - - Ku, C, and old K band receivers

 

absorption line - - absorption of radiation which results from the passage of radiant energy from a continuum source through a cooler, selectively absorbing medium

 

AC - - alternating current electrical power

 

adaptive excision - - using a reference signal, chops out piece of spectrum

 

adaptive canceller - - using a reference signal, removes interference, preserves spectrum

 

AGC - - automatic gain control

 

AGN - - active galactic nucleus

 

AIPS++ - - next generation Astronomical Image Processing System

 

AJ - - anti jam, counter measures to stop jamming signals

 

ALC - - Automatic Level Control

 

aliasing - - the introduction of error into the Fourier analysis of a discrete sampling of continuous data when components with frequencies too great to be analyzed with the sampling interval being used, contribute to the amplitudes of lower-frequency components

 

Allan Variance - - average of the square of the deviation of each sample from the mean of its two adjacent samples, a technique to avoid convergence problems with the true variance in the presence of low frequency behavior

 

ALMA - - Atacama Large Millimeter Array

 

anisotropies - - physical properties that depend on axis through the material

 

AOC - - Array Operations Center

 

aperture - - in a unidirectional antenna, the portion of the plane surface which is perpendicular to the direction of maximum radiation and through which the major part of the radiation passes

apex - - the highest point; the antenna apex is the upper portion of the antenna structure when the antenna is pointing to zenith. The apex describes the location of all the mechanical and electrical hardware supported by the quadrupod. This includes the: Focus Rotation Mount (FRM), Secondary (sub) Reflector, and Feeds (below 1 Ghz). This location also includes the best-fit prime focus line, and as such >apex= and >prime focus= are often used synonymously to describe the same general location on the antenna.

 

array beam - - the effective beam produced by the VLA

 

array gain - - maximum gain of an array or Aarray factor@

 

array response - - image produced by the array given a sky brightness distribution or interference environment

 

ASCII - - American Standard Code Information Interchange, an 8-bit character code

 

ASIC - - application specific integrated circuit

 

ATA - - Allen Telescope Array - 350 small dishes at Hat Creek Observatory

 

ATCA - - Australin Telescope Compact Array - an interferometer array in Australia

 

atmospheric emission - - radiation from earth=s atmosphere

 

attenuators - - device to reduce signal strength

 

auto-correlation - - correlating a signal with itself

 

AWGN - - additive white Gaussian noise

 

azimuth - -angle between true north and the projection of a beam or signal path onto the earth=s surface (east = +90_)

 

band edges - - where amplitude rolls off at edge of frequency band, typically 3dB

 

bands - - see frequency bands

 

bandwidth ratio - - ratio of center frequency to bandwidth

 

bandwidth - - difference in frequency between band edges, usually measured at 3dB points

 

baseband - - signal which is digitized. Also the amplifiers, filters, etc. which deliver this signal to a digitizer

 

baseband pair - - polarization pair at the same frequency

 

baseline - - the distance between two antennas

 

beam - - a flow of electromagnetic radiation concentrated in a parallel, converging, or diverging pattern

 

Beowulf clusters - - a cluster of Linux computers, see www.beowulf.org, offered by Scyld Corporation, www.scyld.com

 

BGA - - ball grid array, type of IC package

 

BIMA - - Interferometer Array at Hat Creek, California

 

bits - - binary digit - a unit of information equal to 1 or 0

 

blind pointing - - pointing with all known systematic effects encapsulated in the a priori model, but no Ajust-in-time@ corrections

 

BNC - - coax connector type

 

Boifot junction - - also see E. Wollack, NRAO Elee. Div Internal Report N0303, Ma, 1966. This is an orthomode junction of enhanced symmetry in which the side-arm port is realized by identical ports on each side of the main arm. These ports are then combined by symmetrical E-plane bends. It is described by A. M. Boifot, E. Lier, and T. Schaug-Pettersen in ASimple and Broadband Orthomode Transducer@, IEE Proceedings, Vol. 137, Pt. H, No. 6, December 1990, pp. 396-400.

 

 

BTUH - - British Thermal Unit times hours, as caloric measure (watt is the preferred unit)

 

bulkhead - - a connection panel

 

byte - - a group of bits, usually 8

 

Cassegrain - - a telescope configuration using a primary, sub reflector, and focus at the center of the primary where the prime focus is behind the sub reflector; see Gregorian

 

C-band - - see frequency bands

 

CCIR - - Consulative Committee on Radio Interference - a standards body providing technical support to the ITU

 

CDL - - NRAO Central Development Lab

 

CDMA - - code division multiple access-cellular transmission technique

 

CDR - - critical design review

 

CEB - - central electronics building, aka CB

 

centroid - - (also center of gravity) weighted mean of a two dimensional distribution

 

CFHT - - Canada France Hawaii Telescope at Mauna Kea

 

checksum - - a summation of bits or digits summed according to a set of rules and used for error detection purposes

 

chirp - - a radar term for pulse compression using linear FM modulation (saw tooth)

 

chromatic dispersion - - dispersion caused by differences in refraction with frequency or wavelength

 

chromosphere - - lower part of sun=s atmosphere, mostly hydrogen gas, where short centimeter and millimeter radiation arises

 

CMEs - - coronal mass ejections

 

CMP - - control & monitor processor - interface device to existing VLA monitor and control system

 

coherent - - a signal having a frequency and phase fixed in relationship to a reference signal

 

comb - - selection of a number of specific frequencies typically equally spaced

Common Operational Model - - how we plan to run this thing

 

commutator - - the part of the armature to which the coils of a motor are connected to convert AC to DC

 

comparators - - a circuit for selecting the larger of two signals

 

complex - - having real and imaginary (orthogonal) components

 

complex envelope form - - baseband form times the carrier exp^(j*omega*t)

 

compression point - - signal level at which a nominally RF device=s gain is reduced by a certain amount due to compression

 

cone - - the feed support and receiver housing

 

continuum - - the continuous spectrum that would be measured for a body if no absorption or emission lives were present

 

CORBA - - Common Object Request Broker Architecture, a vendor-independent architecture an infrastructure that computer applications use to work together over networks, see www.omg.org

 

corona - - the sun=s high atmosphere, where decimeter radiation arises

 

correlation - - taking the product of 2 (real or complex) signals and integrating the results over time

 

COTS - - commercial off the shelf, ie, buy rather than build

 

covariance matrix - - a matrix whose elements are the autocorrelations and crosscorrelations

between antennas (in an array) or taps (in a tapped delay line. More commonly, a matrix describing the relation between the errors in statistically determined quantities

 

cross-correlation - - correlating 2 different signals (also just correlation)

 

cross-polarization isolation - - a measure of cross talk between orthogonal polarizations

 

CRS - - Central Reference System

 

cryogenic - - very low temperatures, typically <110K

 

DAC - - digital to analog converter, D/A

 

dB/km - - free space loss in dB per kilometer distance

 

dB - - decibel, a logarithmic measurement

 

dBc - - dB reference to the carrier

 

dBm - - dB referenced to 1 milliwat

 

DDC - - Direct Digital Controller. A control product manufactured by Staefa used at VLA and VLBA for PID control of HVAC systems

 

DDS - - direct digital synthesizer

 

decimation - - a reduction of sampling rate

 

deconvolution - - example: determination of a true brightness distribution from an image made with a known point spread function

 

delta - - a change, difference

 

demultiplexing - - separating two or more signals that had been previously combined into a single channel

 

depolarization - - reduction of a polarized signal due to instrumental or propagation effects

 

DHC - - data handling computer

 

dichroic - - does different things to two different frequencies

 

dielectric - - electric field can pass with minimum dissipation of power

 

digitizer - - sampler and ADC

 

domain - - all units with the same dimension; e.g. all values in seconds are time domain, all values in Hz are frequency domain. Also, address group for internet such as A.edu@ or A.org@

 

doppler - - change in observed frequency due to relative motion between source and observer

 

downconversion - - mixing a band of frequencies with a local oscillator to produce a lower frequency band

 

DRAO - - Dominion Radio Astronomy Observatory

 

DSP - - digital signal processor

 

DTS - - Digital Transmission System

 

DWDM - - dense wavelength Division Multiplexing, an optical technology used to increase bandwidth in existing fiber optic back bones

 

dynamic range - - ratio of maximum signal level to noise level, typically in dB. More commonly in radio astronomy, ratio of maximum signal to quiescent signal level

 

e2e - - (end-to-end) a data management term to describe computerized observing tasks starting with the observing proposal and ending with data analysis

 

eigen values - - mathematical terms used to simplify matrix analysis of electromagnetic problems

 

Electro Absorption (EA) modulators - - modulation by absorbing an input carrier

 

element beam - - the beam of each of the VLA 25 meter antennas, (also antenna beam or primary beam)

 

EMC - - electromagnetic compatibility

 

EMI - - electromagnetic interference

 

emission - - electromagnetic radiation

 

EMS - - environmental monitoring system

 

encoder - - typically a device to measure relative or absolute position

 

end-to-end - - see e2e

 

epoch - - a precise instant that is used as a fixed reference datum, especially for stellar coordinates and orbital elements. Often misused to mean equator and equinox - the fundamental planes of celestial coordinates

 

ESD - - electrostatic discharge

 

Ethernet - - a local area network where a computer wanting to communicate broadcasts to all. Acknowledgment establishes the link. Also 1EEE 802.3 standard. CSMA/CD access method to handle simultaneous demands

 

EVLA - - Expanded Very Large Array

 

excision - - signal removal by >cutting out=, typically involving interfering signals with limited frequency or temporal range

 

eye pattern - - a digital display of modulated carrier of showing discrete bits within a bit time. There are blank areas or Aeyes@; the clearer the eye, the better the bits are separated

F-rack - - VLA vertex room equipment rack housing LO and control modules (F12 & F14) that control L,X,K,Q band receivers, the IF switch for X & Q, and power supplies

 

Fanout - - the number of parallel loads that can be driven from an output

 

Faraday rotation - - polarization rotation of an electromagnetic beam when passing through a magnetized ionized medium

 

FDM - - frequency division multiplexing

 

feed de-icers - - heaters to melt ice from feed window

 

feed circle - - location of feeds at Cassegrain focus to permit access to different feeds by rotating the subreflector

 

feed- - a horn-like metallic device to couple an RF beam from the antenna to a waveguide or coax

 

FEM - - finite element model or method

 

FET - - field effect transistor, typically selected for very high input impedance

 

FFT - - Fast Fourier Transform

 

fiber optic - - glass waveguides for propagation of modulated light signals

 

filters - - electronic device that passes only certain frequencies

 

finite element - - a discrete element in a physical system used in an approximation method

 

FIR - - Finite Impulse Response digital filter whose impulse response is limited in time

 

FITS - - Flexible Image Transmission System - a common digital format for exchanging astronomical data

 

Flash Memory - - an EEPROM (electrically erasable program moble read only memory) that can be erased and reprogrammed in blocks instead of one byte at a time which makes flash faster

 

FOTS - - Fiber-Optic Transmission System

 

FPDP - - Front Panel Data Port - a data transmission protocol

 

FPGA - - Field Programmable Gate Array

 

frame - - in communications, a packet of transmitted information

frequency bands - - a range of frequencies accepted by a single receiver

4 band------74MHz

P band------327MHz

L band------1-2 GHz

S band------2-4 GHz

C band------4-8 GHz

X band------8-12 GHz

Ku or U-----12-18 Ghz

K band-------18-26.5 Ghz

Ka band------26.5-40 Ghz

Q band-------40-50 Ghz

W band-------80-96 GHz

 

frequency synthesizer - - a flexible tuneable oscillator whose output frequency bears well known relationship to its input frequency

 

fringe rotation - - refers to pulling small phase and frequency offsets into the LO synthesizers in order to make the fringes of the interferometer stationary at the input to the correlator

 

fringe pattern - - the periodic spatial response of an inteferometer

 

fringe - - the alternate addition and subtraction introduced by interference of two or more signals

 

Front Ends - - receiver components after the feed and including the first mixer

fs - - fempto second, 10^-15 seconds

 

FSK - - frequency switched keying-signal modulation process

 

FTE - - full time equivalent to 1 person working full time

 

FX - - correlator in which a FFT precedes the crosscorrelation

 

G/T sys performance - - Gain/System Temperature

 

GaAs - - Galium Arsenide, a semiconductor system

 

Gauss - - unit of magnetic induction

 

Gaussian statistics - - bell-shaped curve

 

Gbits - - 10⁺⁹ bits

 

GBT - - Green Bank Telescope

 

GHz - - gigahertz, 10ž cycles per sec of frequency

 

Glish - - a scripting language used together with a C++ library for developing applications in AIPS++ primarily for data analysis and telescope control

 

GPS - - Global Positioning System. Satellite constellation that transmits accurate times (from which the position of the receiver can be deduced)

 

Gregorian - - a reflecting telescope where the prime focus is in front of the sub reflector; see cassegrain

 

gray code - - a positional binary number notation organized so that adjacent codes differ in only 1 bit

 

Gsps - - giga samples per second (also GS/S)

 

gyroresonance - - the frequency at which an electron spirals around a magnetic field

 

H1 - - neutral hydrogen; also its emission frequency, 1421 MHz

 

headroom - - additional range in gain or other characteristic over what is needed for application (see dynamic range)

 

HEMT - - high electron mobility transistor

 

heuristic - - rule of thumb to improve performance

 

hexadecimal - - base 16

 

HII region - - a region of predominantly ionized hydrogen in interstellar space

 

Hilbert transorm - - the transform, of a function f(x) realized by taking the integral of f(x) [1+cot(y-x)/2]dx; used in FIR filters to generate a 90 degree phaseshift

 

holography - - topographic measurements of a radiating surface determined by measuring amplitude and phase of the resulting radiation

 

horn - - feed

 

HST - - Hubble Space Telescope

 

Hubble flow - - Hubble=s law which states that the recession velocity of a distant extra galactic object is directly proportional to its distance

 

HVAC - - heating, ventilation, and air conditioning

hybrid - - a combination of two or more technology types. Also, a four port device having two outputs which are the sum and difference of the two inputs

 

Hydrogen MASER - - an ulta stable oscillator which uses the change in state of the hydrogen electron to produce a frequency standard

 

IC - - integrated electronic circuit, chip

 

IDT - - manufacturer of bridge and router communication equipment

 

IEEE - - Institute of Electrical and Electronic Engineers, Inc. An international professional and standards organization

 

IF - - intermediate frequency resulting from the mixing a local oscillator with the received signal; also the cable and amplifier carrying this signal

 

IGM - - intergalatic medium

 

image rejection - - rejection of unwanted mixer sideband

 

impedance - - a resistance to current flow with real and imaginary components

 

incoherent - - not coherent

 

InP - - indium phosphide, a semiconductor system

 

INR - - interference to noise ratio

 

insertion loss - - the difference between the power received at the load before and after the insertion of apparatus at some point in the signal path

 

interference - - any undesired signal entering a receiver system

 

interferometry - - measuring coherence between wave fronts received at different locations

 

intermodulation - - unintentional mixing of two signals, typically due to a nonlinearily

IPAC - - Infrared Processing and Analysis Center; integrated phase and amplitude controller

 

IPM - - interplanetary medium

 

ISM - - inter stellar medium

 

isolation - - a measure of separation between signals or between polarizations of the same signal

 

isolators - - a device to provide isolation

 

ISR - - interference to signal ratio

 

ITU - - International Telecommunications Union. A forum for establishing world wide agreement on radio frequency allocations

Java - - object oriented language like C++

 

Jitter - - short time scale variations in phase or frequency

 

Jy - - Jansky, a measure of spectral power flux density where 1 Jansky = -260 dBW/m²/Hz

 

K - - degrees Kelvin

 

K band - - see frequency bands

 

Ka band - - see frequency bands

 

kHz - - kilohertz, 10³ cycles per second of frequency

 

Ku band - - see frequency bands

 

kVA - - kilo volt amperes, a measure of electrical power

 

lags - - in a correlator, the time introduced between signals, retardation, tau

 

L band - - see frequency bands

 

LCP - - left circular polarization

 

LEAF - - large effective area (optical) fiber

 

linear - - A system where the output is proportional to the input, with a possible constant offset. Mathematically, y = a+bx

 

linearity - - a measure of how linear a system is

 

Linux - - a unix-like operating system used on PCs

 

LMS - - least mean squares

 

LNA - - low noise amplifier

 

LO - - local oscillator

LOFAR - - a proposed 0.01 - 0.24 GHz telescope array

 

LSB - - least significant bit

 

LST - - Local Sidereal Time (Astar@ time)

 

LTA - - Long Term Accumulator

 

LVDS - - low voltage differential signaling, a family of digital ICs

 

magnetosphere - - a volume around the earth or any other planet in which particles are more sensitive to the earth=s magnetic field than the sun=s

 

main beam - - Main beam and Primary beam and element beam are used synonymously to describe the main lobe of an antenna=s radiation pattern referenced to the pointing (or optical) axis of the antenna. This term should not be confused with the synthesized beam of the interferometer

 

main dish - - main reflector panel of radio telescope, primary

 

master-slave - - in a flip-flop IC, the master receives information on the leading clock-edge, the slave on the trailing edge. In communications, only the master can initiate communication

 

matched filter - - maximizes the peak pulse signal to noise ratio

 

MCC - - monitor control computer

 

MDL- rank estimator - - minimum description length; a method for estimating the number of eigen values of a covariance matrix which is associated with signals (as opposed to noise)

 

MEMS - - micro electro mechanical systems

 

mezzanine - - a printed circuit board added as a second level to another board

 

MHz - - mega Hertz-10⁶ cycles/second

 

MIB - - module interface board, a communication board for the monitor and control system

 

micro controller - - a single chip computer

 

middleware - - software that provides additional services to an application using a lower level system

 

MIL - - military specification

 

MIPS - - million instructions per second

 

MMIC - - millimeter monolithic integrated circuit

 

modulo n - - a counter with n unique states

 

Moore=s Law - - the observation made in 1965 by Gordon Moore of Intel that the number of transistors per square inch on integrated circuits doubles every year. Now redefined to say data density doubles every 18 months

 

MOS - - metal oxide semiconductor

 

mosaicing - - taking observations at multiple, adjacent points and using the data thus obtained to make an image covering an area larger than a single primary beam, tesselation

 

Mpc - - mega parsec

 

MSB - - most significant bit

 

MTBF - - mean time between failures, a maintenance management term

 

MTTR - - mean time to repair, a maintenance management term

 

multipliers - - output equals product of inputs

 

MUX - - multiplexer, selects one of a number of inputs and passes flat signal to the output

 

MV - - minimum variance

 

narrowband - - narrow range of frequencies

 

NASA - - National Aeronautics and Space Administration at University of Illinois

 

NCSA - - National Center for Supercomputing Applications at University of Illinois

 

noise power - - power generated by random electromagnetic process

 

noise figure, also noise factor - - receiver temperature/room temperature

 

non-recirculating - - not recirculating; see recirculation

 

non-stationary - - time variable statistics

 

NRAO - - National Radio Astronomy Observatory

 

NRC - - National Research Council, Canadian equivalent of NSF

 

NRE - - Non-Recurring Engineering

 

ns - - nano second, 10^-9 seconds

 

NSF - - National Science Foundation

 

nyquist interval - - maximum separation in time which can be given to regularly spaced instantaneous samples of a wave of bandwidth w for complete determination of the wave form of the signal, 2 w seconds

 

Observe - -

 

OH masers - - an astronomical source emitting microwave radiation characteristic of the hydroxyl (OH) molecule

 

ohms - - a measure of resistance to electrical current

 

OMT - - orthomode transducer

 

optical telescopes - - used for observing at IR and visible wavelengths

 

optics - - the reflecting path of a telescope

 

order of magnitude - - X 10

 

orthomode - - provides perpendicular components

 

OSHA - - Occupational Safety & Health Administration

 

OSP - - connector type

 

OSSP - - connector type

 

OVRO - - Owens Valley Radio Observatory - an interferometer array in California

 

PAM - - pulse amplitude modulator

 

parabolic - - a parabola is the locus of points equidistant between a point and a line - dish shape

 

parametric cancelling - - cancellation using a detail model of undesired signals

 

parser - - lexical analyzer

 

parsec - - a unit of measure for interstellar distances. The distance to an object having a parallax of 1 arc second or 3.26 light years

 

passband - - a range of frequencies

 

pattern rumble - - sidelobe gain variations

 

P band - - see frequency bands

 

PC - - personal computer; usually implies an Intel 80X86 compute

 

PCAL - - pulse calibration

 

PCB - - printed circuit boards

 

PDR - - preliminary design review

 

personalities - - the logic setups of a FPGA

 

phase center - - this term is used in reference to the EVLA feed horns. The phase center is the theoretical point on the feed=s optical axis in which all spherical wave fronts emanate. The eight EVLA feed horns used to cover 1 to 50 Ghz are conical corrugated horns. These horns have a phase center region, because the phase center varies with frequency. In practice the phase center is often defined for the mid-frequency of the operational bandwidth of a given feed, and it is the point that the system focus is positioned such that the phase variation across a defined aperture will be minimized

 

phase closure - - vector addition of multiple baseline phases; a measure of successful correlation

 

photosphere - - the luminous surface layer of the sun

 

Pie Town Link - - an analog fiber optic link which passes 200 MHz of VLBA PT IF to the VLA

 

PID - - proportional plus integral plus derivative control; a servoing technique

 

pipeline - - a second instruction begins execution before the first has been completed to speed things up; also any sequence of operations automatically applied to data

 

plasma - - a macroscopically neutral assembly of charged particles

 

plinking - - removal of sinusoidal (single-frequency) signals by estimating their magnitude,

frequency, and phase, followed by subtraction from the original data

 

PLL - - phase locked loop

 

point spread function - - the image representing response of a telescope or array compared to a point source. (Point spread function of an array is also called ADirtybeam@)

 

polarization purity - - a measure of isolation between polarization elements

 

polarization - - a description of the angular distribution of an electromagnetic wave with time of the electric or magnetic field vector at a fixed point

 

poles - - switch terminal; critical point of frequency response determined by LaPlace transform

 

polyphase filter - - parallel processing filter, also brand name

 

power-factor - - ratio of apparent to actual power; watts to KVA

 

ppm - - parts per million

 

PPS - - pulses per second

 

PRI - - pulse repetition interval

 

primary - - the first reflecting surface of a telescope

 

primary beam - - point spread function for individual telescopes in a multi-element interfermeter

 

primary reflector axis - - symmetry axis of the primary reflector

 

prime focus - - focal point of primary reflector

 

PRN - - pseudorandom noise (typically bit sequences which are designed to have minimum correlation except when perfectly aligned)

 

PROM - - programmable read only memory

 

protostar - - a star in the earliest observable stage of formation before the onset of nuclear reaction in the interior

 

ps - - picoseconds 10^-12 seconds

 

PSK - - phase shift keying-signal modulation process

 

PTFE - - poly tetra fluoroethylene - used in RF coax insulation because of minimal phase disturbance

 

pulsar - - a rotating, magnetic neutron star characterized by pulses of energy as the beam of emissions sweeps past the observer once per rotation

PWM - - pulse width modulation

 

QPSK - - quad phase shift keying

 

QSO - - quasi stellar object (an active galactic nucleus)

 

quantization - - a process in which the continuous range of values of an input signal is divided into non-over-lapping subranges. Whenever the signal value falls within a given subrange, the output is given the corresponding discrete value

 

queue - - a scheduling sequence, or processes awaiting scheduling

 

quiescent weight vector - - the desired beamforming weights for the case in which no interference is present

 

radar-mode - - very narrow band width mode for analyzing planetary radar signals

 

radio recombination lines - - a spectral feature produced by electromagnetic radiation at a particular wavelength emitted when an electron in an ionized gas is captured by a positive ion. Energy is released at discrete wavelengths as the electron drops through the energy levels of the atom

 

radio aperture synthesis - - correlating signals from multiple telescopes to form a single image

 

radio synchrotron emission - - electromagnetic radiation emitted by an electrically-charged particles traveling at near the speed of light through a magnetic field

 

RAID - - Redundant Arrays of Inexpensive Disks, a combination of multiple small, inexpensive disk drives which yields performance exceeding that of a SLED (Single Large Expensive Drive). See www.uni-mainz.de/~neuffer/scsi/what_is_raid.html

 

rank detector - - something which estimates the number of Asignificant@ (non-noise) eigen vectors

 

raster-scan - - a technique to access every element on a plane one point at a time by scanning across the plane one line at a time, then moving to the next line

 

RBW - - resolution band width

 

RCP - - right circular polarization

 

real-time - - response within a fixed latency interval

 

recirculation - - recirculation stores data samples in a memory and replays them into the correlator multiple times at different offsets to get varying time differences

referenced pointing - - use of derived offsets from the a priori model obtained during observing

 

refractive interstellar scintillation - - rapid variation in brightness of an object caused by random refraction in turbulent layers in ISM

 

return loss - - the ratio in dB of the power incident upon the discontinuity in a transmission line to the power reflected from the discontinuity

 

RFI - - radio frequency interference

 

RISC - - reduced instruction set computer

 

rms - - root mean square: a measurement of a signal taken by squaring data points along the curve, finding the mean, taking the square root

 

RPC++ - - remote procedure call (computer communication protocol)

 

RRLs - - radio recombination lines

 

RTOS - - real time operating system

 

sampler - - analog to digital converter synchronized with a clock (digitizer is preferred word)

 

S band - - see frequency bands

 

SCFM - - standard cubic foot per minute

 

SCSI - - Small Computer System Interface pronounced ( Ascuzzy@). A parallel interface standard for attaching peripherals to computers

 

SDR - - signal-to-distortion ratio

 

SDRAM - - synchronous dynamic randomly addressable memory. Runs faster than conventional DRAM

 

sensitivity - - the ratio of cause to response; also, the inverse of Tsys

 

SFDR - - spurious-free dynamic range; the difference between the maximum signal power at which the system is still linear and the power associated with the spurious product in that condition

 

SHARC - - super Harvard architecture computers; also a trade name for a family of DSP micro processors by Analog Devices, Inc.

 

sheilded twisted pair - - a twisted pair of copper conductors covered with a conductive shield

side lobe - - a radiation of an antenna in any direction except the major lobe

 

SiGe - - Silicon Germanium, a semiconductor material; also a manufacturer of 2.46 Hz linear power amplifiers for Blue Tooth applications

 

sigma - - symbol for standard deviation

 

sine - - a locus of points representing the ratio of the opposite side of an acute triangle to the hypotenuse as the side varies from 0 to maximum value

 

SINR - - signal-to-interference-plus-noise ratio

 

SIR - - signal to interference ratio

 

SIS - - super conductor-insulator-super conductor mixer used for millimeter wave RF LNA

 

SKA - - Square Kilometre Array-next generation radio telescope

 

skew - - angular or time displacement between parallel signals

 

Sloan - - short for SDSS - Sloan Digital Sky Survey Observatory, Apache Point, NM

 

SMA - - connector type

 

SMT - - surface mount technology; type of IC package

 

SNR - - signal-to-noise ratio

 

SOIDA - - analog digital input/output system test fixture for measuring performance of receivers

 

SONET - - Synchronous Optical Network, a standard for connecting optical fiber transmission systems; SONET OC (optical carrier) 192 is 10⁶, bps, for example

 

sparse array - - an array with typical element spacing >> lambda/2

 

spatial frequency - - sinusoidal variation with location

 

speckling - - a power intensity pattern produced by the mutual interference of partially coherent beams that are subject to minute temporal and spatial fluctuations, modal effect

 

spectral channels - - the frequency resolution elements of a spectrometer

 

spectral resolution - - frequency difference between spectral channels

 

spectroscopy - - the study of spectra

SPI - - serial peripheral interface is a general purpose synchronous serial interface implemented on some micro controllers

 

splatter - - adjacent channel interference due to over modulation of a transmitter by abrupt peak audio signals

 

SRG - - Shift Register Generator

 

stitching - - the seamless reassembly of the spectra taken at different but overlapping frequencies

 

straw man concept - - an incomplete design set up to initiate discussion.

 

STScI - - Space Telescope Science Institute

 

subarrays - - a group of antennas in an array set aside for a separate, concurrent observation

 

subband processing - - breaking a wide bandwidth into smaller bands for independent processing, typically to allow delays to be treated as phase shifts

 

subreflectors - - 2nd reflecting surface of a cassegrain radio telescope

 

subspace - - lower-dimensional parts of a Aspace@; Example: the x-y plane is a 2-D subspace of the x-y-z (cartesian) coordinate system

 

synthesizer - - see frequency synthesizer

 

system efficiency budget - - a maximum value permitted for losses in a system

 

system efficiency - - ratio of output to input

 

system temperature - - see Tsys

 

taper - - design of feed

 

TCB - - time code generator box

 

TCP/IP - - Transmission Control Protocol/Internet Protocol, the suite of communications protocols used to connect hosts on the internet

 

TDM - - time division multiplexing

 

TDMA - - time division multiple access

 

Terabytes - - a billion bytes, 10^-9

 

throws - - number of switch positions

 

THz - - terahertz, a frequency of 10⁹ cycles per second

 

Torr - - a unit of pressure used to measure vacuums, 1 torr will support 1 mm Hg under standard conditions

 

transducers - - a device that converts energy from one system to another

 

Trx- - receiver temperature; a measure of thermal performance of a radio receiver

 

Tsys - - System temperature; a measure of thermal performance of radio telescope

 

TTL - - Transistor-Transistor Logic; an early family of digital integrated circuits

 

Tully-Fisher distance - - relationship between width of H1 radiation from spiral galaxies and their absolute photographic magnitude; a technique to estimate distances

 

turn-key - - complete, operational system

 

U band - - see frequency bands

 

UDP - - User Datagram Protocol, a connectionless protocol that runs on top of IP protocol; it is usually packaged with TCP, a connection based alternative

 

UPS - - uninterruptible power supply

 

USB - - Universal Serial Bus, an external bus standard that supports data transfer rates of 12 MbPS and up to 127 peripheral devices on a single port

 

UTC - - universal time coordinated; civil time referenced to Greenwich, England, with effect of Earth=s wobble averaged

 

UV - - ultra violet; a frequency band just above visible band

U,V - - projection of a baseline on the plane perpendicular to the incoming radiation u,v data - correlation measured at given u,v locations (Fourier transform of image data)

 

VAC - - volts alternating current

 

Van Vleck correction - - statistical correction when digitizing a small number of bits

 

VCXO - - voltage controlled crystal osciullator

 

VDC - - volts direct current

vertex - - the antenna vertex is the lowest point in the shaped parabola when the opening of the parabola is pointing to zenith. This can also be described as the point on the shaped parabola curve where the slope is zero. The vertex may also describe a general location on the antenna such as the >Vertex Room=, which is located in the vicinity of the antenna vertex

 

VHDL - - very high density logic-a family of digital ICs

 

virtual - - being such in effect, but not in actual fact; an object that appears to exist, but is not, somehow Areal@

 

visibility - - the real and imaginary components that result from multiplying (correlating) the voltages received from two telescopes and integrating; one Fourier component

 

VLBA - - Very Long Baseline Array

 

VLBI - - very long baseline interferometry

 

VSWR - - voltage standing wave ratio

 

Walsh functions - - rectangular waveforms with values ⁺1. The n^th order Walsh functions are orthoganol on an interval of Zⁿ clocks. This makes them useful as an imposed modulation to cancel systematic effects

 

watch-spring azimuth cable wrap - - spiral wrap up used to minimize bend radius, used on VLBA

 

wave guide septum - - a type polarizer-passive waveguide apparatus which separates LCP & RCP

 

waveguide - - a device such as a metallic pipe or optical fiber which guides the propagating electromagnetic waves along a defined path

 

W band - - see frequency band

 

WBS - - Work Breakdown Structure

 

WDM - - wavelength division multiplexing

 

WIDAR Correlator - - Wideband Interferometric Digital Architecture, a correlator design by DRAO

 

wideband - - a wide range of frequencies

 

windowing - - a taper applied to (typically) time domain signals to suppress end point effects; in particular, for spectral estimation

 

WVR - - water vapor radiometer, a device to measure signal absorption resulting from water vapor in the atmosphere

 

Wye - - the infrastructure of the Y-shaped VLA

 

X band - - see frequency bands

 

XF - - type of correlator where correlation is done before Fourier transform, see FX

 

Xilinx - - A manufacturer of FPGAs

 

YIG - -Yttrium iron-garnet crystal for microwave frequency source; also a YIG based oscillator

 

zeeman measurements - - splitting of spectral lines into a number of components when the source is in a magnetic field