Note:  Send additions and/or corrections  to Terry Romero .






Additional Sources:


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, offered by Scyld Corporation,


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


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 or


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


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 nth 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