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A Subsystem Test Bed for the Frequency‐Agile Solar Radiotelescope

This paper describes the design and operation of the Frequency‐Agile Solar Radiotelescope (FASR) Subsystem Testbed (FST) and the first observational results. Three antennas of the Owens Valley Solar Array have been modified so that each sends a 1–9 GHz band of radio frequency to a central location using a broadband analog optical fiber link. A dynamically selected 500 MHz subset of this frequency range is digitized at 1 Gsps (gigasample per second) and recorded to disk. The full‐resolution time‐domain data thus recorded are then correlated through offline software to provide interferometric phase and amplitude spectra on three baselines. An important feature of this approach is that the data can be reanalyzed multiple times with different digital signal‐processing techniques (e.g., different bit‐sampling, windowing, and radio frequency interference [RFI] excision methods) to test the effect of different designs. As a prototype of the FASR system, FST provides the opportunity to study the design, calibration, and interference‐avoidance requirements of FASR. In addition, FST provides, for the first time, the ability to perform broadband spectroscopy of the Sun with spectrograph‐like spectral and temporal resolution, while providing locating ability for simple sources. Initial observations of local RFI, geostationary satellite signals, global positioning system (GPS) satellite signals, and the Sun are presented to illustrate the system performance.