NRAO Home  >  Green Bank  |  Wiki Topic:    GB > Data > DataDictionary

Changes | Index | Contents | Search | Statistics | Jump to Topic

 Data Dictionary

This glossary was adapted for wiki from http://www.gb.nrao.edu/GBT/MC/doc/data.html on 20 Jul 2004.

accessor

a manager that oversees the access to- and the routing of- the data produced by various telescope devices. It's responsibilities include the creation and managing of the relationships between monitor clients and providers. The accessor maintains information about all of the monitor data aquisition activities at any time on the system.

archivist

a manager that generates FITS files with time-stamped rows of values from Monitor & Control (M&C) data monitor samplers, which are selected by the user, and is generally used for engineering purposes.

axis

a physical movement of a mirror either by a linear or rotational movement.

backend

any device that is used to digitize the IF or accept digitized IF to produce backend data. Backends have high speed control of the receiver through the switching signals. A backend may be either a master or slave to these signals.

backend data

the formatted data from a backend capturing all the information the backend has access to describing the scan.

balancer

a detector plus attenuator for maintaining a specified level.

clock

provides Universal Time Coordinates (UTC).

command set

a set of attribute values for a device which completely defines its commanded behavior during a scan.

continuum backend

a backend used for measuring total power of a received signal.

converter

changes a signal from one frequency range to another by mixing the input signal with one or more LO frequencies.

cryogenics

the equipment used to super cool the receivers; these require no automatic interfacing beyond direct control by the operator and monitoring.

data associated parameters

the selected monitor information for inclusion into observational data; describes those measured aspects of the scan which may affect the data, but cannot be controlled by the system i.e., the experimental conditions.

detector

a monitor for measuring RF or IF energy at specific points in the system.

device

a well-defined sub-system of the telescope such as the LO, receiver, spectral processor, or the antenna used for controlling the independent variables of a scan. A telescope may be thought of as an aggregate of devices requiring synchronization and control for accomplishing scans.

dish

the primary mirror for collecting RF signals. It has two axes of movement: elevation and azimuth. Azimuth is defined in terms of plus or minus 270 degrees with zero south of cable wrap.

feedhorns

the final mirrors to affect the RF signal before passing to the receiver. Currently this mirror has only one axis for secondary receivers: rotation. It is actually adjusted by moving the receiver box. The feedhorn for the primary receiver has in addition to rotation, focus and translation axes.

FITS

Flexible Image Transport System: written format of all data files.

frontend

one or more sets of receiver and converter(s) plus associated electronics for producing an IF signal from the received RF.

GO

GBT Observe.

holography

a backend for performing holographic surface measurements via satellite signals.

LO

Local Oscillator: a synthesizer, produces one more more tones.

M&C

Monitor & Control.

mirror

any device that affects the antenna's beam by physical movement of its axes. Movements of all secondary mirrors is specified relative to the boresight, i.e., a canonical beam path between the dish and receiver. Movement of the primary mirror (dish) is defined relative to the local gravity reference frame.

monitor

provides access to internal parameters of a device.

observational data

the combination of command sets, data associated parameters, and backend data. End product of a scan.

observer

the prime "customer" of the telescope; a person who controls telescope observing during a specified period of time.

operator

the on-duty person responsible for the safety of the telescope and its personnel. Arbitor of all control access to the telescope.

phase calibrator

marks the delay of the IF for VLBA observing by inserting "birdies" synchronized to the maser into the receiver.

pointing

a system which determines the true pointing of the antenna, by means other than the servo system. For the GBT, these systems include the metrology, pointing model, and weather station.

prime focus feedarm

supports the prime focus frontend and must be extended to use the primary frontend, and retracted to use any secondary receiver on the turret.

receiver

a collector of RF signals. It amplifies the collected RF signal at the end of the boresight.

receiver select

places a frontend in the boresight path, by manipulating the arm, turret, and elevation axis.

registry

a type of accessor which creates data files in FITS for both engineering logs and data associated parameters.

RF

Radio Frequency.

RFI

Radio Frequency Interference.

round-trip phase monitor

measures the synchronization of the LOs standard by comparing the standard at the maser and at the LO.

router

a device for controlling signal routes. Current plans includes routers for the IF, LO, test, and switching signals. This may include patch panels and splitters as well as electronic switches.

sampler

a device that converts a continuous-time signal into a discrete-time sequence of its samples; produces FITS files

scan

a contiguous period of time when data is collected under constant, prespecified experimental conditions. Measured conditions which cannot be controlled completely enough (pointing) or at all (weather) are captured as data associated parameters.

scan coordinator

a manager that produces a FITS file called the scan log; there is one scan log for each project.

specifier

defines all experimental conditions for running a scan and iterating through a series of scans. It provides the observers' user-interface.

spectral processor

a high-speed spectrometer backend.

spectrometer

a backend used for spectroscopy.

spectrum analyzer

used for displaying and capturing spectrum from IF signals. Will be used on the telescope for monitoring the IF for interference.

subreflector

a mirror used between the dish and receivers on the turret. The subreflector has six axes: three translations and three tilts.

surface actuator

a motor and measurement detector (LVDT) that produces controlled movement of a corner of the dish's panel(s). An axis for surface panels.

surface panel

a mirror controlled by 2209 surface actuators which control the dish's shape.

switching signal

a binary signal i.e., cal, sig/ref, various blankings, advanced sig/ref and repeat, for high-speed control between the backends, frontends, and LOs.

transporter

a device that receives data from samplers on a host and sends data to the accessor.

turret

a turntable used to place secondary receivers in the boresight reflected from the subreflector.

vacuum pump

used to aid in the cooling of receivers.

VLBA

an object normally used to act as both a specifier and a backend for VLBA antennas.

ULO

Universal Local Oscillator: a local oscillator (LO) capable of varying its frequency dynamically during an scan. It's frequency is varied to compensate for Doppler shift by reading positions from antenna, or for frequency switching through switching signals.

weather station

a set of instruments for providing weather reports.

-- RonDuPlain - 24 Jan 2005