The NRAO tape-recorder interferometer system

Several tape-recorder interferometer systems have been constructed in the last few years. These systems are used for connecting existing radio-telescope systems into interferometers, with baselines ranging from a few kilometers to nearly the diameter of the earth. The NRAO Mark II interferometer system is in wide use. This, and the fact that its properties are typical of those of such systems in general, justifies a detailed description of the system. The system is based on a television-type rotating-head video recorder. One-bit sampled data are recorded at a 4-Mb rate. After recovery, the data are processed in special-purpese digital devices and general-purpose digital computers to complete the interferometer system. For purpose of this description, the software is regarded as an intrinsic part of the system.