Note: Send additions and/or corrections to Terry Romero tromero@nrao.edu .
GLOSSARY
Additional Sources: http://www.webopedia.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 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