| 2,27 → 2,27 |
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| \sec Current radioastronomy problems |
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| From radioastronomer point of view its important radioastronomy has interest in primarily natural signals from surrounding universe. Radio astronomy do not have interest in terrestrial civilisation made signals. |
| From a radioastronomer's point of view it is important that radioastronomy focuses its interest primarily on natural signals originating in the surrounding universe. It does not pay attention to the man-made signals created by our civilisation. |
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| Radioastronomy has a big problem at now. It is because many terrestrial transmitters are active at this moment. All terrestrial transceivers made dense signal mixture which can cause troubles not only to radioastronomers. |
| In consequence, there exists attempts to control radiofrequency spectrum. As result of attempts to control the radiofrequency spectrum, the frequency allocation table was created. \fnote{\url{http://www.ukaranet.org.uk/basics/frequency_allocation.htm}} Radio-frequency allocation table table contain special bands allocated to radioastronomy use. But for many reasons this bands are not clean enough for directly use in radioastronomy observations. As result we cannot work by same way as radioastronomers in the beginning of radioastronomy. Many experiments namely, Cosmic microwave background detection and pulsar detection cannot be realised in its original form with acceptable results. |
| However, it is due to these signals, that the current radioastronomy faces a disturbing problem. The problem arises from the fact, that there are many terrestrial transmitters active at the moment and all of them are sources of a dense signal mixture which can cause trouble not only to radioastronomers. |
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| Supporting evidence of such effect is RadioJOVE project. NASA engineers which come with RadioJOVE project has great idea. |
| RadioJOVE project brings opportunity for creating publicly available cheap radioastronomy receiver. But they used an old fashioned construction model which can work in desert, but it simply cannot work in modern civilisation as it is know in Europe. |
| Origin of its dysfunction is presence of strong radiofrequency interferences. This interferences are orders of magnitude stronger than Jupiter decametric emissions. |
| From practice about light pollution mitigation we also know that there are not much chance to improve this situation radically in radiofrequency spectrum. |
| As a consequence, there already exists attempts to control radiofrequency spectrum. As result of attempts to control the radiofrequency spectrum, the frequency allocation table was created. \fnote{\url{http://www.ukaranet.org.uk/basics/frequency_allocation.htm}} Radio-frequency allocation table table contains special bands allocated to radioastronomy use. However, for many reasons these bands are not clean enough to be used directly in radioastronomy observations. As a result, we cannot work in the same way as had the radioastronomers in the very beginnings of radioastronomy. Many experiments, namely Cosmic microwave background detection and pulsar detection, cannot be nowdays realised in their original forms with satisfactory results. |
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| There are not other ways that searching for new methods for radioastronomy observations. New methods which allows us to work without completely clear radiofrequency bands and which allow us to see surrounding universe trough man made radiofrequency interference mixture. One solution is use of already known natural radio frequency signals parameters. Natural signals usually have different signal properties from local interference. Natural object do not have a problem with transmitting in bandwidth of tens megahertz in sub 100 MHz bands. This object are usually far away and the same signal could be received at almost half of Earth without any significant differences. But it is also clear that signal parameters have drawbacks in reception power. The reception power of radioastronomy object is 1e9 smaller than signal power received from typical broadband radio transmitter. |
| Supporting evidence of such effect is RadioJOVE project. NASA engineers who originally created the RadioJOVE project had a great idea. The RadioJOVE project brought an opportunity for creating a publicly available, cheap radioastronomy receiver. However, they used an old-fashioned construction design, which on one hand can operate in desert, but on the other it simply did not meet the criteria allowing its use in modern civilisation, as it is know in Europe. |
| The source of its dysfunction is a presence of strong radiofrequency interferences. These interferences are orders of magnitude stronger than Jupiter decametric emissions, whose detection was the main aim of the RadioJOVE project. |
| From what we already seen in the light pollution mitigation pursuit, there is only a small chance to radically improve the situation in radiofrequency spectrum. |
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| From above mentioned facts about natural radio signals is clear one result. Modern requirements on radioastronomy receiver are complete different from requirements in history. Radioastronomy is not limited by access to electronic components today, but it is limited by presence of electronic everywhere. |
| The only way to overcome this problem is to search for new methods of radioastronomy observations. New methods which allows us to work without completely clear radiofrequency bands and which allow us to see the surrounding universe even despite the existence of a man-made radiofrequency interference mixture. One solution is to use already known natural radio frequency signals parameters. Natural signals usually have different signal properties than local interference. Natural objects do not have problems with transmitting in bandwidths of tens of megahertz in sub 100 MHz bands. These objects are usually far away and the same signal could be received at almost half of the Earth globe without any significant differences. On the other hand, it is obvious that signals with such parameters have some drawbacks, namely in the reception power. The reception power of radioastronomical object is 1e9 smaller than signal power received from a typical broadband radio transmitter. |
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| From the above mentioned facts concerning the natural radio signals we can conclude that modern requirements imposed on a radioastronomy receiver are completely different from the requirements existing back in the history. Radioastronomy is no longer limited by an access to electronic components, today it is rather limited by the everywhere presence of electronic. |
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| \sec Modern Radio astronomy receiver |
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| In beginning of radioastronomy receivers were constructed as simple station with single antenna or multi antenna array with fixed phasing. This approach were used due to limits of previous electronics components and technology. Main challenges were noise number and sensitivity due to poor characteristic of active electronic components such transistors and vacuum tubes. |
| In the beginning of radioastronomy, the receivers were constructed as simple stations with single antenna or multi antenna array with fixed phasing. This approach was used because of the existing limits of electronic components and technologies. Main challenges of those times were the problem of noise number and low sensitivity, both present due to the poor characteristics of active electronic components such as transistors and vacuum tubes. |
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| Most of today operational radioastronomy equipments were constructed in this manner. They were constructed usually shortly after WWII or during The Cold War as parts of military technology. |
| Most of the present-day operational radioastronomy equipments were constructed in similar manner. They were produced usually shortly after the WWII or during The Cold War as a part of military technology. |
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| But today we have access to components with quality, repeatability and price is completely district from components accessible for previous generation of radioastronomers. Then we could develop better radioastronomy equipment which will be powerful enough for make new astronomy discovery.\fnote{Most of astronomy related discoveries in last fifty years came from radioastronomy.} |
| Today we have an access to components having quality, repeatability and price completely different from the components accessible by previous generation of radioastronomers. That is why we can develop better radioastronomical equipment, powerful enough to make it new astronomical discoveries possible.\fnote{Most of astronomy-related discoveries in the last fifty years came from radioastronomy.} |
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| We could develop a receiver which will have wide bandwidth, high Third-order intercept point and ideally has an option for phase and frequency locking to other receiver on another radioastronomy site of planet. Several receivers which have such parameters currently exists USRP2, USRP B210 or HackRF and are commercially available. But all of them lacks scalability and have high prices. However scalability and redundancy is main requirement which is requested by noise reduction algorithms. |
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| 30,7 → 30,7 |
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| \secc Observation types |
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| Today radioastronomy knows several observation types. |
| Current radioastronomy knows several types of observations. |
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| \begitems |
| * Spectral observations |
| 38,7 → 38,7 |
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| * Velocity observations |
| \enditems |
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| All of these observations ideally needs high frequency resolution and stability. Wide observation bandwidth in hundreds of MHz is usually desirable for easier differentiation of source types. |
| All of theme ideally needs high frequency resolution and stability. Wide observation bandwidth in hundreds of MHz is usually desirable for easier differentiation of source types. |
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| \sec Required receiver parameters |
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