Takes an IF signal converted to baseband and samples it.
Converts the sampled signal from an analog to a digital data format.
Formats and time stamps this data for either VLBI or VLBA use depending on the observing program plan or mode.
Sends the data to a tape recorder, VHS or reel to reel, either directly or via components housed in the S2 recorder rack.
A simplified block diagram of the VLBI DAS electronics is included as Figure 3. This diagram illustrates the signal path through the system's various components. Note: For simplicity, only major components have been included. Please refer to actual schematics of this system for a detailed view of all VLBI DAS electronics.
The GBT operator is responsible for assisting astronomers in carrying out their observing programs using VLBI/VLBA equipment. Refer to the GBT Operations Manual, procedures and checklists for specific guidance on setting up and operating this system.
Observing using the VLBI DAS requires interaction with various computer systems, each responsible for carrying out various functions required for a successful observing run.
A Unix based system is located in the VLBI Equipment Room and is used to carry out various functions for setting up the system for an observing run, preparing tapes for recording, and monitoring data collection. A typical console display on this system is normally divided into 8 different regions or windows to allow monitoring of system status as well as the input of user commands. Refer to this system's user manual for specifics on program options and their use.
Monitoring the state, status, and controlling additional set-ups of equipment for VLBI observing is done using Control Library for Engineers and Operators (CLEO) applications. These applications are run from the operator's control room workstation. In addition to their primary monitoring function, this software package can also be used to manually control observing functions. Specific information concerning CLEO applications is included in the on-line CLEO Manual.
Observing with the GBT and using its variety of backend instruments will be done interactively through graphical control screens or by running pre-planned observing tables. This interface uses a "windows" type environment. Setting up various GBT instrument and backend devices may be accomplished in both automated and manual modes depending on the observers plan. Specifics' concerning this software, and how it can be used in connection with VLBI observing is discussed in the software's users manual. Please refer to it as necessary.