Radio Astronomy

The following frequencies are generally accepted spectral regions for radio astronomical observations in radio astronomy. There are others frequencies, but I've chosen to list the regions that maybe most accessible by an amateur radio astronomer.

  • 13.360 – 13.410 Mhz
  • 25.550 – 25.670 Mhz
  • 37.5 – 38.25 Mhz
  • 73 – 74.6 Mhz
  • 150.05 – 153 Mhz
  • 322 – 328.6 Mhz
  • 406.1 – 410 Mhz
  • 608 – 614 Mhz
  • 1.4 – 1.427 Ghz
  • 1.6106 – 1.6138 Ghz
  • 1.66 – 1.67 Ghz
  • 2.655 – 2.700 Ghz
  • 4.8 – 5 Ghz
  • 10.6 – 10.7 Ghz

The above bands are based on Australian Radiofrequency Spectrum Plan - Radiocommunications Act 1992

The lower segments are used for solar and Jupiter observations; the 73, 150 and 406 MHz segments are quite popular for pulsar, and the 1.4 Ghz band is used for hydrogen line measurements, which seems to be the most popular with many amateur radio astronomer. Aslo made even more so by the Seti League Program

In very simple terms the equipment to build a Radio Telescope are:

  • A sensitive radio which can receive one of the above frequencies.
  • A radio with "No" AGC (automatic gain control) or has the ability to turn it off.
  • A high gain low noise pre-amp and a directional antenna which can be pointed at the sky.
  • A Data Logger to record total signal strength of the radio over a period of time

The signal strength of the radio is recorded over a period of time, signal levels will increase and decrease as a radio emitting object passes across the sky. Over number of days it is possible isolate radio astronomical observations from ground and satellite interference.

Radio Astronomy links:
Radio astronomy - Wikipedia, the free encyclopedia
Hydrogen line - Wikipedia, the free encyclopedia
The Parkes Observatory
Amateur radio astronomy with SIMPLE 20 MHz arrays


Mapping the Radio Sky

Using a method called “Meridian Drift Scan Observation” it is possible to build up an image of the sky at radio frequency not visible using optical telescopes. As seen below.


The Radio Sky: Tuned to 408MHz Credit: C. Haslam et al., MPIfR, SkyView

Drift scans plot the sky line by line using the earths rotation from East to West then adjusting the antenna every 24 hours over a series of elevations separated by somewhat less than the angular beamwidth of your antenna. If you had a beamwidth of say 10 degrees, you would then lower the elevation by about five to seven degrees and making a strip chart for that elevation. You would continue the process until the beam was point a bit above your horizon and then combine the data to make a 2 dimensional map of the sky. In reality, there is quite a bit more to do this, but this is the basic Idea.

Here are some more examples:
The Infrared Sky (and more)


Radio interferometry

Radio interferometry is a powerful tool that can be used for a number of diverse applications. A radio interferometer consists of more than one antenna tuned to receive radio emissions from the desired frequency. The signals from the receivers are then cross-correlated to produce a "fringe pattern". This fringe pattern can then be analysed to produce a result ranging from an image of a distant astronomical object to the location of a nearby terrestrial or extra-terrestrial radio emitter.

Links:
Fringe Dwellers - Simple Radio Interferometry
History of astronomical interferometry