This web page is a user's guide to the operation of the original data acquisition system for the NRAO phased array feed (PAF) system. This data acquisition system consists of the first BYU 40-channel receiver, a 40-channel analog-to-digital converter consisting of 10, 4-channel ADLink ADC cards, and 10 rack mounted PC's that host the ADC cards. Each PC has a 1 TB disk drive for data storage. These 10 drives are accessable as directories on a linux file system where the data can be collated. The 10 ADC host PCs are Windows machines named paf1 through paf10 (web address paf[1-10].ad.nrao.edu). The linux PC is paf0 (web address paf0.gb.nrao.edu).
The PAF system is designed for use on the GBT and includes the dipole array, cryogenic amplifiers, an L-band fiber optic signal transmission system, a frequency conversion and band-limiting analog receiver, and the digital data acquisition back-end. The dipole array, cryogenics and fiber-optic transmitters are in the PAF front-end box. Everything at the other end of optical fibers is in the Jansky Lab "tape room" adjacent to the GBT control room. The front-end box may be at the GBT prime focus, the focus of the 20-meter telescope, or the outdoor test building. There are optical fibers from each of these locations to the "tape room".
The PAF system may be run stand-alone, as when performing tests and calibration in the lab or outdoor test building, or as a GBT receiver/back-end in coordination with telescope control. Figure 1 shows Ethernet socket the connections between the software components of the PAF system. The dashed lines in Figure 1 represent socket messages used to setup the PAF system and initiate data acquisition. The socket messages are described in a separate document (to be attached here). The "PAF Rcvr GUI" is the graphical user interface for stand-alone control and shown in Figure 2. This software module is replaced by GBT Monitor and Control when used on the telescope.
Two file types are produced by each data acquisition scan: a raw data file from each of the ADC host computers (paf1 through 10) and a FITS file that contains all of the hardware setup parameters for that scan. The raw data files are written to the one-terabyte drives on the ADC host computer in the directory D:\Data\[prog name]\, where [prog name] is the character string assigned to this data acquisition session. When running under GBT control this will be the name assigned to the test or observing program by the telescope schedule administrator plus an observing session serial number, e.g., AGBT08B_014_07. When running the PAF system stand-alone the [prog name] is the user's choice and may be entered in the designated text window on the GUI screen. The FITS file will be written in the Linux file system. Under GBT control this will always be in the directory /home/gbtdata/[prog name]/RcvrArray1_2/. In stand-alone mode any accessable directory may be specified in the designated text window on the GUI screen.
As shown in Figure 1, the "9812_GBT" server, whose code file is 9812serverGBT.py, accepts messages from the stand-alone GUI manager or GBT Control system and distributes them to the ten PCs that host the ADC cards. All ADC host PCs receive the same messages. The socket connections between the "9812_GBT" server and the ADC host PC's are permanent connections. The startup sequence must be "9812_GBT" first and then each of the 9812PAF.executables in any order. The "9812_GBT" server code in 9812serverGBT.py is hard-coded near the top of the code file to know which ADC host machines to expect. For test purposes this is only "paf1", but for full PAF data acquisition this must be changed to a full Python list of machine names. If either the server or any of the 9812PAF.exe executables are terminated, all must be terminated and restarted, server first then 9812PAF.exe executables. This is a rather tedious procedure, but it should need to be done infrequently. Do not log out of a machine running the server or any of the 9812PAF.exe executables, but you may "Disconnect" from a Remote Desktop connection.
The GPIB server translates socket messages into GPIB instructions for the signal ganerators that act as local oscillators, ADC clock, and phase monitor tone burst. These instruments are connected to the host PC, "papillon", with a USB to GPIB adapter cable. Typically, the instruments are set once at the beginning of an observing run. The default values set when the server is started should be the correct values for the PAF receivers and data acqusition system. The user only needs to change the sky frequency to the required value.
The FITS server collates setup information from the GPIB and ADC servers, assembles it into FITS format, and writes this into a new FITS file at the beginning of each data acquisition scan. The FITS file will be written in the Linux file system so this server must run on a Linux machine. Under GBT control this will always be in the directory /home/gbtdata/[prog name]/RcvrArray1_2/. In stand-alone mode any accessable directory may be specified in the designated text window on the GUI screen.