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As a consequence, there already exist effort to control the 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 or pulsar detection, cannot be nowadays realised in their original forms with satisfactory results. 

As a consequence, there already exist effort to control the radiofrequency spectrum. As result of attempts to control the radiofrequency spectrum, the frequency allocation table was created \cite[radio-astronomy-frequency]. 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 or pulsar detection, cannot be nowadays realised in their original forms with satisfactory results. 

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 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 transmission 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.

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 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 transmission 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 $1*10^9$ smaller than signal power received from a typical broadband radio transmitter.

If we look at actual spectrum occupancy in Europe (measured in power spectral density)  we see that signal dynamic range in spectra

If we look at actual spectrum occupancy in Europe (measured in power spectral density)  we see that signal dynamic range in spectra 

easily reaches more than 80 dB above natural noise levels. If we don't want to deal with receiver saturation or poor sensitivity we need a receiver and digitalization unit which has comparable dynamical range of with received signals. This imply use of least 14 bit ADC without any spare of range.   

easily reaches more than 80 dB above natural noise levels \cite[spectrum-observatory]. If we don't want to deal with receiver saturation or poor sensitivity we need a receiver and digitalization unit which has comparable dynamical range of with received signals. This imply use of least 14 bit ADC without any spare of range.   

Only few digitalization systems dedicated for radioastronomy exists nowadays.  Currently existing systems use either custom design of the entire receiver or they are constructed from commercially available components. The attempts to use open-source solutions in the radioastronomical field are still rather scarce.

Only few digitalization systems dedicated for radioastronomy currently exists.  Currently existing systems uses either custom design of whole receiver or they are constructed from commercially available components. Open-source principle attempts are very rare in radioastronomy field. 

Custom designs usually use non-recurring engineering techniques for the development of specific solutions for observational projects. Thus the costs of these instruments are mostly very high as long as they are not produced in larger quantities. A typical example of an instrument developed and manufactured in one piece with enormous founding drawn is Arecibo ALFA survey multi beam feed Array. 

Custom designs usually uses non-recurring engineering  for development specific solution for observation project thus costs of this instruments are very high if developed instrument are not reproduced many times. Typical example of instrument developed and manufactured in one piece with enormous founding resources draws is Arecibo ALFA survey multi beam feed Array. 

Another example illustrating the opposite of custom receiver and digitalization unit design is LOFAR system developed by Astron in Netherlands. \url{http://arxiv.org/abs/1305.3550}

Another opposite example for custom receiver and digitalization unit design is LOFAR system developed by Astron in Netherlands \cite[lofar].

LOFAR is an innovative radioastronomical system which uses the phased antenna array approach in extensive scale with thousands (around $2*10^4$) of antennas manufactured an deployed on the field. The centre of LOFAR system is situated in Netherlands and peripheral antennas and connection network are extended to other European countries. 

LOFAR is innovative radioastronomy system which uses the phased antenna array approach in enormous scale and thousands (around $2*10^4$) of antennas are manufactured an deployed on field. The centrer of LOFAR system is situated in Netherlands and peripheral antennas and connection network are extended to other European countries. 

LOFAR project must use low cost hardware due to its large scale. Special construction techniques are used to keep the overall project budget at an acceptable level (take the specially designed polystyrene supporting blocks for HBA antennas as an example). Many of the components used are manufactured in mass scale for other than scientific purposes. LBA antennas masts are made of standard PVC plastic waste pipes and LOFAR uses low cost direct sampling receivers. The whole project has been designed by Netherlands Institute for Radio Astronomy, which produces many similarly sophisticated devices. \url{http://www.astron.nl/other/desp/competences_DesApp.htm}

LOFAR project must use low cost hardware due to systems scale. Special construction techniques are used to keep overall project budget at acceptable levels (specially designed polystyrene supporting blocks for HBA antennas for example). Many of used components are manufactured in mass scale for other than scientific use LBA antennas masts are made from standard PVC plastic waste pipes and LOFAR uses low cost direct sampling receiver. Whole project has been designed by Netherlands Institute for Radio Astronomy, which produces many similarly sophisticated devices\cite[astron-devices]. 

Due to the cost restrictions in science and astronomy instruments' development, a reuse of engineering work turns out to be very useful. There is only one modular digitalization and data processing system currently in existence - it is called CASPER and it is under development at Berkley university since around 2005. \url{https://casper.berkeley.edu/wiki/Main_Page} as CASPER's designers an engineers remarkably noticed a lack of such hardware in radioastronomy. Their ideas are summarised in the following paper \url{https://casper.berkeley.edu/papers/200509URSI.pdf}. Unfortunately they use proprietary connector standard and technology and develop modular system based purely on Tyco Z-DOK+ connectors family.  Z-DOK connectors are high quality differential pairs connectors, but price of these connectors (around 40 USD) is comparable with the cost of one ADC channel in the design described in our thesis. \url{http://www.digikey.com/product-detail/en/6367550-5/6367550-5-ND/2259130}. 

Due to cost restrictions in science and astronomy instruments development, an reuse of engineering work should be useful. One modular digitalization and data processing system currently exit. It is being developed at Berkley\cite[casper-project]. CASPER is in development from around 2005. CASPER's designers an engineers remarkably noticed a lack of such hardware in radioastronomy science, theirs ideas are summarised in paper \cite[casper-paper]. Unfortunately they use proprietary connector standard and technology and develops modular system based purely on Tyco Z-DOK+ connectors family.  Z-DOK connectors have relatively high pricing (around 40 USD) \cite[Z-DOK-connectors].  Z-DOK connectors are high quality differential pairs connectors, but price of these connectors is comparable with value of one ADC channel in our design described in following part of document. 

In contrast to professional astronomers which use proprietary digitalization units, amateur radioastronomers currently use multichannel sound cards \url{http://fringes.org/} or self designed digitalisation units. Devices constructed by amateurs are usually non-reproducible \url{http://wwwhome.cs.utwente.nl/~ptdeboer/ham/sdr/} . It is evident that current radioastronomy lacks a proper hardware which could be used by both communities - professionals and amateurs. Optimal solution for this situation would be an open-source hardware. 

In opposite to professional astronomers which uses proprietary digitalization units, amateur radioastronomers currently uses multichannel sound cards \cite[amateur-fringes] or self designed digitalisation units. Devices constructed by amateurs are usually non reproducible \cite[amateur-sdr] .  It is evident that current radioastronomy lacks of proper hardware which could be used on both communities - professionals and amateurs. Optimal solution for this situation should be open-source hardware.