Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
How a Radio Telescope Works Outline Introduction – purpose – basic terms Satellite TV System – similar to radio astronomy – system description Radio Astronomy System Overview Antenna Front end – Key components – Key design considerations – Sample systems Back end Purposes – Continuum – Spectral line – Pulsar – VLBI Key Techniques – Switching – Averaging Examples of backends Satellite TV System Antenna—redirects energy to a point Feed—collects energy for LNA LNA—”low noise amplifier” amplifies signals Cable—transposrts signal Tuner—selects signal for viewing TV—displays signal VCR—records displayed signal for later viewing Couch potato—creates a need, supplies $$ Basic Radio Telescope control computer Front End Preamplifies radio waves and extracts information (the signal) Back End Further amplifies signal until strong enough to be analyzed. All components inside dashed line are in the control room. Electronics Control room Parabolic dish reflector concentrates radio waves to antenna focal point where electronic processing begins. Systems Control Positions telescope, directs observing, monitors receiving systems. Data Collection Displays and monitors individual data. Records while observations are in progress. Analysis Computer Does preliminary analyses of accumulated data. Computer display Magnetic Tape Stores raw data for later and more thorough analysis Data recording and analysis equipment How a Radio Telescope Works • Basic Terms – Time Domain • Something plotted VS Time – Usually voltage or power – Frequency Domain • Something plotted VS Frequency Time Domain Flashlight Battery Voltage VS Time 3.5 3 Voltage 2.5 2 1.5 1 0.5 0 1 2 3 4 5 6 7 Time (hours) 8 9 10 11 Frequency Domain Key Componets • Antenna – The bigger the better – Needs accurate surface – Limits: mostly money • Feed – Collect ONLY signals from the antenna • Amplifier – Don’t want them to ADD noise. – Usu. Cooled to -432〫F Basic Front Ends Direct Detection Type G Feed RF Amp B Filter To Backend for Detection Input spectra BPF 1 Response BPF 2 Response f fR fR-fL BPF 2 BPF 1 mixer Local oscillator f fL fR Front End Feed Backends power Y pulsar VLBI Spectral line continuum X frequency Key Techniques • Switching or Differencing – Study the difference between two or more data sets • Averaging – Noise is random – Desired signal is not – Averaging reduces noise by Root N Pulsar Dispersion VLBI References • M.L Meeks, Methods of Experimental Physics: Astrophysics, Vol. 12, Academic Press (1976) • J.R. Fisher, “Digital Continuum Receiver Users’ Manual,” NRAO Electronics Division Internal Report No. 243 (1984). • A. M. Shalloway et. al., “Autocorrelation Receiver Model IV: operational Description,” NRAO Electronics Division Internal Report No. 234 (1983).