Beginner’s Tab
Purchasing a radio telescope isn't like buying an optical telescope. They are harder to find, and usually require assembly and software troubleshooting. In some cases a radio telescope must be built from components. Unlike optical telescopes, radio telescopes are found in a greater variety and each type is used for very specific observations. All radio telescopes have at least have 3 basic components: the antenna, the receiver, and the output recorder. First, let’s identify how a beginner can start in radio astronomy.
There are lots of ways to get involved in radio astronomy but they are rarely obvious and do not always offer immediate gratification such as when looking through an optical telescope. Most radio telescope packages involve some construction and software set-up by the user, and that can be time consuming and frustrating especially if there are no clear instructions to guide the amateur. Nonetheless, it is a very rewarding intellectual endeavor to keep you busy to the end of your life. Beginners usually purchase one of the 3 types of radio telescopes, which cost less than $200 each.
1. The Itty Bitty Telescope, IBT, though simplistic as it seems, can offer you some unusual observations if you know what to look for. If you purchase one, don’t be in a rush to give it away. You’ll find uses for it as your radio astronomy sophistication grows, such as satellite tracking. http://www.aoc.nrao.edu/epo/teachers/ittybitty/procedure.html
2. Radio Jove, for the observation of Jupiter storms, requires a big backyard space. If you don’t have such space, you may want to hold off on that one. http://www.radio-astronomy.org/node/211
3. Another type of radio scope, SuperSID, allows you to collect real data from the ionosphere resulting from solar activity. You can then send this data to the University of Sanford database. http://www.radio-astronomy.org/node/210
The Astronomical League has a radio astronomy observing program, and that can guide you in a disciplined approach. As you gain sophistication, you might want to try radio meteors, the INSPIRE unit http://theinspireproject.org/default.asp?contentID=27, and SDR dongles.
As you explore radio astronomy, reading and watching videos on the subject will help understand more about the field. Located on SARA main page menu bar, is the Education tab that offers instructional links.
A good starting point for a radio telescope is to check out this page on the SARA website. Getting Started in Radio Astronomy | Society of Amateur Radio Astronomers
“Introduction to Radio Astronomy” is a presentation from the July 2015 SARA Conference:
http://www.radio-astronomy.org/node/240
A very good video presentation on microwave antenna demonstrations is available on the SARA site at:
http://www.radio-astronomy.org/node/238.
Also located on the SARA main webpage menu bar is a link for projects:
http://www.radio-astronomy.org/projects
Two other good primers are:
http://www2.jpl.nasa.gov/radioastronomy/
http://www.cv.nrao.edu/course/astr534/ERA.shtml
Attending a SARA conference will also help in your efforts to learn more about radio astronomy. The annual conference at NRAO in Greenbank, WV provides instruction on a 40-foot radio scope that is available for personal use throughout the conference. An instruction class is given on the first day of the conference so that you can use the device immediately.
Skynet University offers an online class that allows use of a 20 meter radio telescope dish. Information of the class is found at:
http://skynet.unc.edu/introastro/ourcouses/
Use of Skynet is also a complimentary benefit in some local astronomy clubs, and for a small fee, is also available to individuals. Local astronomy clubs might also have radio astronomy instrumentation for your use. SARA Grant programs, http://radio-astronomy.org/grants, make it possible for students and teachers to explore radio astronomy.
Radio Astronomy Principles
Once a beginner identifies a radio telescope and project, one needs to understand what is being observed. Radio astronomy is more than just observing. Equipment, instruments, and confounding factors are all important in understanding observational features as well as observational errors. Visual astronomy is much more simple in this respect. Even with access to radio telescopes, it is not a simple process of viewing something with the human eye.
Radio telescope sensitivity is a measure of the relationship between the signal and the noise. The signal is the power detected by the telescope from the astronomical phenomena. The noise is mostly thermal from electronics but also ground radiation entering the feed horn and the cosmicmicrowave background and other interference.
The dominant sources seen in the radio sky are the Sun, supernova remnants, radio galaxies, the Milky way. The quiet Sun has a typical flux density of 105 Jansky (Jy) while the next strongest sources are the radio galaxy Cygnus-A (Cyg-A) and the supernova remnant Cassiopeia-A (Cas-A), both of which have flux densities of 10E4 Jy. Sources as bright as 1 Jy are relatively rare. Whereas the limiting magnitude of an optical telescope is easily determined, the limiting sensitivity of a radio astronomical receiver is much more complicated. The gain and noise figure of the LNA are important, as well as the noise pollution in the local vicinity. Use of several equations, such as the radiometer equation, can provide a rough estimate of a radio telescope’s abilities.
There are nearly eight orders of magnitude between the strongest and weakest sources that an amateur might detect. The level of equipment sophistication required to detect these sources will therefore vary considerably – from a standard communications receiver to detect solar bursts, to special temperature controlled receivers and preamplifiers to detect galaxies. Almost all amateurs begin by detecting the Sun. This is easy to do. The next goal might be to detect Jupiter. Access to larger and more sophisticated radio telescopes will lead to observing a supernova remnant such as Cassiopeia. With this level of sensitivity, it is then possible to make maps of radio noise in the Milky Way (continuum method) and to detect and plot the distribution of the neutral Hydrogen emission line at 1420.4MHz (spectrometer method). The moon is a solid body with no significant atmosphere; it therefore radiates as a cool solid body (thermal radiation) and is not easy to detect at long wavelengths. It is possible for the amateur to make observations with access to an old C band (4 – 8 GHz) satellite TV antenna with a diameter of a few meters. The thermal signal from the Moon is quite low and a fairly good receiver is needed to make a successful detection.
If you have a radio telescope for amateur radio astronomy, which signals can it record? Radio waves coming from space are almost always very weak. Aside from the Sun whose radio emission is easily recordable due to its proximity, other signals are so weak that it is difficult to identify them with respect to background noise. This makes mandatory the use of special receivers specially developed for radio astronomy and antenna as large as possible in order to increase the received signal level.
A sophisticated amateur with a parabolic antenna diameter of 2.3 meters, could record signals from the most powerful radio sources in the Universe. The list is not long and it varies depending on working frequency based on physical characteristics of the object. Some in fact emit more radio waves at high frequency and therefore a receiver (that records in the range of X-band or 8-12 GHz frequency)is suitable for receiving. Among these sources include the Sun, the Moon, Orion A (which corresponds to Orion Nebula, M42) and Taurus A (which corresponds to Crab Nebula, M1). Other objects emit more at low frequency and require receivers that record lower frequencies (such as waves at 1420 MHz frequency, i.e., L-band at 1-2 GHz). Here we find the center of our galaxy, (Sagittarius A), Cassiopeia A and Cygnus A.
Radio astronomy is a fascinating area of technical endeavor and is open to people with some engineering skill. It does not require vast expenditure as much of the equipment can either be home-constructed or obtained from amateur radio outlets. Some attention to detail is required and patience is needed to assemble and perfect the receiver system to enable the detection of very weak signals withstable gains and a constant low noise background.
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SARA is dedicated to the exploration of radio astronomy at the amateur level. Many amateurs are engaged in developing hardware, software, and methodologies to expand the limits of amateur radio observation. Such amateurs impose intriguing opportunities. With peer review, they can develop new approaches to radio astronomy observation, or offer an equally valuable dissertation on explanations to misidentified radio observations and their nature. SARA welcomes positive diversity of opinion but does not necessarily embrace those opinions as it own.