Data Dictionary

accessor: manages 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.
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.
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: 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 UTC.
command set: 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: equipment used to super cool the receivers. These require no automatic interfacing beyond direct control by the operator and monitoring.
data associated parameters: 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: 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: 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: 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.
holography: a backend for performing holographic surface measurements via satellite signals.
LO: a synthesizer, produces one more more tones.
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: 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: 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.
receiver: 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.
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.
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.
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: binary signal i.e., cal, sig/ref, various blankings, advanced sig/ref and repeat, for high-speed control between the backends, frontends, and LOs.
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: an 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.