The amateur radio astronomy presents some initial difficulties and obstacles of technical nature due to the specificity of this discipline and the limited availability of dedicated instrumentation and support for the neophyte (RadioAstroLab is an exception...).
It's a discipline that requires a minimum of knowledge in parallel sectors such as physics and astrophysics, astronomy, electronics (installation and management tools), mechanics, computer (data acquisition and data processing). For best results it is desirable to set activity in the style of teamwork.
The main difficulties faced by the passionate radio astronomy are due to:
The received signals are very weak (typical power levels ranging between 10-15 e 10-20 W) with characteristics similar to a noise.
There are problems with the internal noise, with the gain fluctuations and temperature of the receiver (they are large amplitude when compared with the changes in the useful signal).
The typical level of the received signal is much less than the background noise.
There are significant problems with electromagnetic interference of artificial origin.
Account should be taken of the natural noise from the soil, the atmosphere...
Visiting the massive and complex structures of the radio astronomy official research is clear the high level of expertise and specialization of researchers, together with the "astronomical" costs of the structures needed to compete successfully in scientific competition. This can easily discourage the modest amateur projects if there are not clear the attainable limits and the objectives of the work.
Deal seriously with radio astronomy means to set an experiment where individuals or groups of fans (radio amateurs, astronomy...) can lead to interesting activity, including official support.
Must be clear about the limits reached and a firm will to invest time and patience in the correct approach to a discipline which is manifested in a very immediate and less "spectacular" than other observational techniques (such as optical astronomy).
We are not sensitive to radio waves: the "visualization" of the scenario observed and "extraction" of information that comes from his observation is not immediate.
We need instruments (radio telescopes) can detect radio signals and convert them into usable information.
These difficulties make, in the eyes of the profane, radio astronomy much less accessible and "dark" than optical astronomy.
Given the wavelength of the visible radiation and the structure of our eyes, we are able to directly visualize the scenario observed in the form of color image with a sufficient degree of detail for our survival daily needs.
The use of systems of optical amplification, together with appropriate geometries of opening instrumental, allows to increase the sensitivity of our senses to observe better and farther.
The wavelength much greater than the radiation, together with the need to use appropriate "transducers" that reveal the information coming from the observed scenario, make difficult and not immediate formation of "radio images": there are required complex, expensive and bulky instrumental means to obtain data of "visual quality" comparable to optical.
These difficulties are well known to those involved in professional astronomy, they are amplified when it comes to amateur astronomy.
If the approach of the fan is the mentality acquired during the experience in optics, will be weak motivation to begin and, especially, keep a good experience of amateur astronomy.
You need to be electronic experts to deal with amateur radio astronomy?
There are two possibilities:
- For those who have practical knowledge of electronics, can be found on the web a lot of information on the construction of radio telescopes and instruments to start experiments in amateur radio astronomy.
- RadioAstroLab offers tools and accessories that allow the installation of amateur and semi-professional radio telescopes of varying complexity and cost.
The question of the data interpretation
The success of most radio astronomy experiments, together with the ability to deliver scientifically interesting and well documented results, is conditioned by the concrete possibilities of cooperation between groups of fans: it is well known to those who know and appreciate the experimental scientific method, as are indispensable and independent confirmations on several observations relating to a phenomenon considered unusual or interesting. These instrumental confirmations are based on any correlations between the observed data produced by independent investigators that "look" at the same event.
It's very important that researchers participating in the experiment using a suitable instrumentation to the phenomenon to be observed, with similar specifications and performance, despite their possible diversity, are useful to confirm the registration of the phenomenon and its correct interpretation.
Only in this way you can be sure that you have "captured" and recorded a special event.
When confirmed by the most independent observers, the analysis of the phenomenon can finally be published and made known to the official research institutes: they recognize the correctness, reliability and usefulness of the method of work adopted by amateurs.
The correct interpretation of the acquired data is one of the most delicate and complex radio astronomy research, especially the amateur, given the exiguity of technical means and the not always "proven" experience of the investigators.
Are well known, for example, who is responsible for the reception of natural phenomena in the ELF-VLF bands, or the recording of the radio bursts (in the band decametric) of Jupiter or the Sun, the difficulty in distinguishing the signals produced by the phenomena under study (expected or hoped to observe) from those generated by electromagnetic disturbances and noises that afflict the local observations characterized by a very thorough level of instrument sensitivity.
In these emblematic cases, of the difficulties encountered in amateur radio astronomy research, it is useful to have a "network" of observers located at some distance from each other (diversity reception space) equipped with receiving equipment similar to continuously monitor of the same phenomenon, with which it is possible to compare the data and to study correlations among these: the local interference will be present only in one of the recordings, while the astronomical event will leave in all track (more or less evident).
The mechanism of thermal radiation is characterized by the fact that the energy emitted by the source increases as the frequency increases, which means that this process prevails at high frequencies.
The Sun, the source warmer and near, emits a very small amount of thermal radiation in the VHF band (neglecting the very intense impulsive components in this region of the spectrum due to mechanisms of other nature), emission that increases in intensity with increasing frequency: this behavior confirms the thermal nature of the dominant radiation when the Sun is "quiet".
The thermal radiation of the Moon is measurable (due to its proximity) only in SHF band: they are usually relatively few "thermal" radio sources accessible to amateur instruments, all, however, "visible" only with antennas characterized by effective enough large area.
The majority of cosmic radio emits according to the mechanism of radiation for synchrotron due to strong accelerations occurring by the electrons in the relativistic motion immersed in an intense magnetic field.
This radiation predominates at low frequencies, the lower end of the radio spectrum, rapidly decreasing in intensity with increasing frequency.
Several radio sources that emitting hard enough in the VHF and UHF bands appear relatively "silent" and difficult to detect with amateur equipment when observed at frequencies of a few GHz.
Delicate is the question of the instrumental resolution, which refers to the ability of the system to "distinguish" (or resolve) two spatially close celestial objects.
For an antenna of allocated size (effective area) that capacity increases with frequency: greater is the effective area of the antenna, is narrower the receive beam and is greater the ability to resolve specific angular detailed in the area of observed sky.
It's possible to increase the resolving power of a radio telescope increasing the effective area of the antenna system, increasing its operating frequency and using interferometric techniques. Everything has a cost and requires a commitment proportional to the required performance.
Problem, not least, is to find a enough wide "slice" of spectrum available for observations in the chosen location for the installation of radio astronomy site.
If the level of interference is high, it can become dominant the criterion for the choice of operating frequency, which minimizes the interference.
It's important to explore the available spectrum using a scanner, a spectrum analyzer or a tunable receiver over a wide range of frequencies: once you have found the "clean" area is monitoring on those frequencies 24 hours to see if the actually can be used throughout the day.
From the experience we have seen that urban areas are almost always unsuitable for radio astronomy observations, since it is almost impossible to find even a small portion of the spectrum, free from interference, except, perhaps, the microwave band (SHF).
A first step may be to determine to which frequencies are more intense the radio sources that interested to study (spectral variation of the emission mechanisms), and then evaluate the intensity of the radiation as a function of frequency), to have an idea on the instrumental resolution request for observation and estimate the actual availability of radio spectrum in the planned installation area (the natural and artificial interference).
Knowing how varied the intensity of radioemission coming from cosmic radio sources as a function of frequency is of particular importance: the two main mechanisms of radiation are the thermal and synchrotron emission (except for some special applications that do not fit into these categories).
- ELF-VLF band (from about 300 Hz to about 300 kHz):
The external radiation are not receivable because are screens by the ionosphere, but you can program very interesting studies to reveal the meteoric activity (ionization of the atmosphere induced by astronomical events).
Interesting correlations with research on "Radio Nature."
The working tools are very cheap, easy to build and install.
- HF band (from about 3 MHz to about 30 MHz):
Receptions are made not too far from the lower limit of the spectrum.
Study of radio storms of the Sun and Jupiter, the study of galactic radiation.
In this frequency band the non-thermal radio sources are particularly intense.
The receivers are not too complicated to build, but the antenna systems are very bulky and characterized by modest directivity.
Very intense artificial interference.
- VHF band (from about 30 MHz to about 300 MHz):
It will be relatively simple the reception of the galactic center, Cassiopeia A and Cygnus A.
Installing a good antenna system coupled with an enough sensitive receiver it may reveal the most powerful pulsar that, because of their mechanism of emission, present a maximum emission precisely in the VHF band. This search is hard enough.
Relatively complex receivers and accessible antenna systems.
Interesting possibilities for modification interventions of amateur radio equipment from the market and/or surpuls on kit receivers proposed by hobby electronics magazines and manufacturers of electronic kits.
Possibility of using modules commercial TV tuner (for electronics experts).
Very intense artificial interference.
- UHF band (from about 300 MHz to about 3 GHz):
In this band, much used by the official research (especially in the years 60 and 70), the radio sources accessible to amateurs are not particularly intense.
The receivers are relatively complex while the antenna systems are relatively accessible.
And it's possible to use recovery TV material (tuner and antennas at low cost).
- SHF band (from about 3 GHz to about 30 GHz):
At microwave frequencies is very important to the thermal component of cosmic radiation and, using not too complicated tools, is relatively simple to receive the Sun, the Moon and other radio sources.
The size of the market reception SAT-TV, GPS and cell phone made available at very advantageous prices, electronic components and modules suitable for the construction of efficient microwave radiometers.
A wide variety of SHF antennas is available on the market.
You can develop interesting amateur activities of "exploration" spectral sky radio astronomy, including amateur SETI searches.
The first instruments proposed by RadioAstroLab exactly operate in this frequency band.
List of websites (developed by individuals, by groups of researchers from amateur and amateur associations) dealing with and explore the issue of amateur astronomy.
Are shown and described many excellent achievements of small radio telescopes operating in a wide range of frequencies, receivers, antennas, test and calibration, automatic data acquisition interfaces (connected to PC) and software for processing and recording data.
Most of the achievements uses electronic components and modules from the market of satellite TV, cell phone, terrestrial plant TV and equipment amateur.
The experiences and observations are often accompanied by records documenting the results and performance of the systems described.
For further details refer to the download section.