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ALFA

ALFA - General Information for Observers

The ALFA receiver frontend was built under contract to the Australia Telescope National Facility (ATNF) of the Australian CSIRO. NAIC is responsible for the IF/LO system, the fiber optic system bringing the 14 IF channels from the Gregorian Dome to the operations building and the back-end fast dump digital spectrometers.

Image credit: Germán Cortés Medellín

The following table lists some general information on the ALFA receiver system. For technical details see the Performance Parameters web page.

Feed-horns 7 beams arranged in an hexagonal pattern. Each beam has dual linear polarization; the polarization isolation is >20 dB

Beam size 3.8 × 3.3 arcmin (beam 0)

Bandwidth 300 MHz

Frequency range 1225 - 1525 MHz. The low frequency limit is set to 1225 MHz by the waveguide cutoff and the OMT (orthomode transducer) performance; the high frequency limit is set to 1525 MHz by OMT resonances and a low-pass filter

Filter bank A 100 MHz filter (centered at 1440 MHz) is available for pulsar observing; the 1390-1490 MHz band is (almost) radar-free

System temperature ~30 K

Gain The central beam has higher gain (~11 K/Jy) than the peripheral ones (~8.5 K/Jy). The gain variation over the bandpass is +1/-2 dB

Calibration noise source The calibration is done by means of a single diode; the diode signal is splitted and injected into each beam. T_cal ~10-12 K (the stability of the diode is improved by maintaining its temperature constant)

Array rotation -100 deg to +100 deg

Backend Processors WAPP (Wideband Arecibo Pulsar Processor) - used for pulsar and spectral line work
GALSPECT - used for Galactic HI work
Mock Spectrometer - used for pulsar, continuum and spectral line work

Feed-horns	7 beams arranged in an hexagonal pattern. Each beam has dual linear polarization; the polarization isolation is >20 dB
Beam size	3.8 × 3.3 arcmin (beam 0)
Bandwidth	300 MHz
Frequency range	1225 - 1525 MHz. The low frequency limit is set to 1225 MHz by the waveguide cutoff and the OMT (orthomode transducer) performance; the high frequency limit is set to 1525 MHz by OMT resonances and a low-pass filter
Filter bank	A 100 MHz filter (centered at 1440 MHz) is available for pulsar observing; the 1390-1490 MHz band is (almost) radar-free
System temperature	~30 K
Gain	The central beam has higher gain (~11 K/Jy) than the peripheral ones (~8.5 K/Jy). The gain variation over the bandpass is +1/-2 dB
Calibration noise source	The calibration is done by means of a single diode; the diode signal is splitted and injected into each beam. T_cal ~10-12 K (the stability of the diode is improved by maintaining its temperature constant)
Array rotation	-100 deg to +100 deg
Backend Processors	WAPP (Wideband Arecibo Pulsar Processor) - used for pulsar and spectral line work GALSPECT - used for Galactic HI work Mock Spectrometer - used for pulsar, continuum and spectral line work