Introduction to Radio Astronomy
R.W. Porcas
Radio waves
- Frequency range 30 MHz - 800 GHz (10m - 0.4mm), factor 30,000
- LOFAR ALMA
Radio emission processes
- Thermal, Synchrotron, free-free, atomic/molecular lines; absorption
Radio telescopes
- Single dishes, azimuth, elevation, HA,DEC Resolution, diffraction limit Surface accuracy, range of telescope sizes
example: Effelsberg 50cm -> 3mm range factor > 100 Focus, focal plane, "pixels"
Instrumentation, receiving systems
- "Feed", polarisation of radiation System noise RF, amplification of feed voltage heterodyne system, LO, IF
"Detection"
- Square-law detection System noise and "signal" noise Bandwidth, integration time, S/N-ratio Output stability, on-off source measurement
Radio disturbances
- atmosphere, ionosphere, interference
==> absorption, emission, Faraday rotation, delay
Simple 2-element interferometer (lead in to next talk !)
- Advantages of an interferometer
- resolution, stability of multiplying interferometer
- Coherence, common polarisation of elements