| /dokumenty/skolni/diplomka/conclusion.tex |
|---|
| 13,6 → 13,10 |
| In the future versions of the system hardware, the Xillybus IP core and driver interface should be swapped with an open-source alternative of PCIe interfacing module or PCIe might be completely avoided. In ADC configuration FPGA module, the SPI configuration data registers read back should be implemented. |
| \nonum \chap Glossary |
| \makeglos |
| \bibchap |
| \usebbl/c mybase |
| /dokumenty/skolni/diplomka/description.tex |
|---|
| 14,7 → 14,7 |
| \sec Required parameters |
| We require the following technical parameters, to supersede existing digitalization units solutions. |
| Primarily, we need wide a dynamical range and high IP3. The receiver must accept wide dynamic signals because a typical radioastronomical signal has a form of a weak signal covered by a strong man-made noise or other undesired noises as lighting, Sun emissions etc. |
| Primarily, we need wide a dynamical range and high IP3. \glos{IP3}{Third-order intercept point} The receiver must accept wide dynamic signals because a typical radioastronomical signal has a form of a weak signal covered by a strong man-made noise or other undesired noises as lighting, Sun emissions etc. |
| Summary of other additional required parameters follows |
| 30,28 → 30,28 |
| \sec Sampling frequency |
| Sampling frequency is not limited by the technical constrains in the trial version. This parameter is especially limited by the sampling frequencies of analog-to-digital conversion chips available on the market and interface bandwidth. Combination of the required parameters -- dynamic range requiring at least 16bit and a minimum sampling frequency of 1$\ $MSPS leads to the need of high end ADC chips which does not support such low sampling frequencies at all. Their minimum sampling frequency is 5$\ $MSPS. |
| Sampling frequency is not limited by the technical constrains in the trial version. This parameter is especially limited by the sampling frequencies of analog-to-digital conversion chips available on the market and interface bandwidth. Combination of the required parameters -- dynamic range requiring at least 16bit and a minimum sampling frequency of 1$\ $MSPS \glos{MSPS}{Mega-Samples Per Second} leads to the need of high end ADC chips which does not support such low sampling frequencies at all. Their minimum sampling frequency is 5$\ $MSPS. |
| We calculated a minimum data bandwidth data rate for eight receivers, 2 bytes per sample and 5$\ $MSPS as $8 \cdot 2 \cdot 5\cdot 10^6 = 80\ $MB/s. Such data rate is at the limit of the actual writing speed of classical HDD and it is almost double the real bandwidth of USB 2.0 interface. As a result of these facts we must use faster interface. Faster interface is especially needed in cases where we require faster sampling rates than ADC's minimal 5$\ $MSPS sample rate. |
| The most perspective interface for use in our type of application is USB 3.0 or PCI Express interface. However, USB 3.0 is a relatively new technology without good development tools currently available. We have used PCI Express interface as the simplest and the most reliable solution. |
| We calculated a minimum data bandwidth data rate for eight receivers, 2 bytes per sample and 5$\ $MSPS as $8 \cdot 2 \cdot 5\cdot 10^6 = 80\ $MB/s. Such data rate is at the limit of the actual writing speed of classical HDD \glos{HDD}{Hard disk drive} and it is almost double the real bandwidth of USB 2.0 \glos{USB 2.0}{Universal Serial Bus version 2.0} interface. As a result of these facts we must use faster interface. Faster interface is especially needed in cases where we require faster sampling rates than ADC's minimal 5$\ $MSPS sample rate. |
| The most perspective interface for use in our type of application is USB 3.0 or PCI Express interface. However, USB 3.0 is a relatively new technology without good development tools currently available. We have used PCI Express \glos{PCI Express}{Peripheral Component Interconnect Express} interface as the simplest and the most reliable solution. |
| \sec System scalability |
| For analogue channels' scalability, special parameters of ADC modules are required. Ideally, there should be a separate output for each analogue channel in ADC module. ADC module must also have separate outputs for frames and data output clocks. These parameters allow for conduction at relatively low digital data rates. As a result, the digital signal can be conducted even through long wires. Modular concept allows a separation from central logical unit which supports optimization of number analogue channels. |
| Clock and data signals will be then handled distinctively in our modular scalable design. Selected ADC chips are guaranteed to have defined clock skew between the sampling and data output clocks. This allows taking data and frame clocks from the first ADC module only. The rest of the data and frame clocks from other ADC modules can be measured for diagnostic purposes (failure detection, jitter measurement etc.), but these redundant signals are not used for data sampling. If more robustness is required in the final application, DCO and FR signals may be collected from other modules and routed through an voting logic which will correct possible signal defects. |
| Clock and data signals will be then handled distinctively in our modular scalable design. Selected ADC chips are guaranteed to have defined clock skew between the sampling and data output clocks. This allows taking data and frame clocks from the first ADC module only. The rest of the data and frame clocks from other ADC modules can be measured for diagnostic purposes (failure detection, jitter measurement etc.), but these redundant signals are not used for data sampling. If more robustness is required in the final application, DCO \glos{DCO}{Data Clock Output} and FR signals may be collected from other modules and routed through an voting logic which will correct possible signal defects. |
| This system concept allows for scalability, that is technically limited by a number of differential signals on host side and its computational power. There is another advantage of scalable data acquisition system -- an economic one. Observatories or end users can make a choice of how much money are they willing to spent on radioastronomy receiver system. This freedom of choice is especially useful for science sites without previous experience in radioastronomy observations. |
| \secc Differential signalling |
| The above mentioned concept of scalable design requires relatively long circuit traces between ADC and digital unit which captures the data and performs the computations. The long distance between the digital processing unit and the analog-to-digital conversion unit has an advantage in noise retention typically produced by digital circuits. Those digital circuits, such as FPGA, Ethernet or other flip-flops blocks and circuit traces, usually work at high frequencies and emit wide-band noise with relatively low power. In such cases any increase in a distance between the noise source and analog signal source increase S/N significantly. However, at the same time, a long distance brings problems with the digital signal transmission between ADC and computational unit. But this obstacle should be resolved more easily in free-space than on board routing. The high-quality differential signalling shielded cables should be used, such as massively produced and cheap SATA cables. This technology has two advantages over PCB signal routing. First, it can use twisted pair of wires for leak inductance suppression in signal path and second, the twisted pair may additionally be shielded by uninterrupted metal foil. |
| The above mentioned concept of scalable design requires relatively long circuit traces between ADC and digital unit which captures the data and performs the computations. The long distance between the digital processing unit and the analog-to-digital conversion unit has an advantage in noise retention typically produced by digital circuits. Those digital circuits, such as FPGA \glos{FPGA}{Field-programmable gate array}, Ethernet or other flip-flops blocks and circuit traces, usually work at high frequencies and emit wide-band noise with relatively low power. In such cases any increase in a distance between the noise source and analog signal source increase S/N significantly. However, at the same time, a long distance brings problems with the digital signal transmission between ADC and computational unit. But this obstacle should be resolved more easily in free-space than on board routing. The high-quality differential signalling shielded cables should be used, such as massively produced and cheap SATA \glos{SATA}{Serial ATA} \glos{ATA}{AT Attachment} cables. This technology has two advantages over PCB \glos{PCB}{printed circuit board} signal routing. First, it can use twisted pair of wires for leak inductance suppression in signal path and second, the twisted pair may additionally be shielded by uninterrupted metal foil. |
| \secc Phase matching |
| For multiple antenna radioastronomy projects, system phase stability is a mandatory condition. It allows a precise, high resolution imaging of objects, increases signal to noise ratios in several observation methods and allows the use of advanced algorithms for signal processing. |
| High phase stability in our scalable design is achieved through centralized frequency generation and distribution with multi-output LVPECL hubs (CLKHUB02A), that have equiphased outputs for multiple devices. LVPECL logic is used on every system critical clock signal distribution hub. LVPECL logic has an advantage over LVDS in signal integrity robustness. LVPECL uses higher logical levels and higher signalling currents. Power consumption of LVPECL logic is nearly constant over the operating frequency range due to the use of bipolar transistors. This minimizes voltage glitches which are typical for CMOS logic. One drawback of its parameters is a high power consumption of LVPECL logic which easily reaches tens of milliamperes per device. |
| High phase stability in our scalable design is achieved through centralized frequency generation and distribution with multi-output LVPECL \glos{LVPECL}{Low Voltage Emitter-coupled logic} hubs (CLKHUB02A), that have equiphased outputs for multiple devices. LVPECL logic is used on every system critical clock signal distribution hub. LVPECL logic has an advantage over LVDS \glos{LVDS}{Low-voltage differential signaling} in signal integrity robustness. LVPECL uses higher logical levels and higher signalling currents. Power consumption of LVPECL logic is nearly constant over the operating frequency range due to the use of bipolar transistors. This minimizes voltage glitches which are typical for CMOS \glos{CMOS}{Complementary metal–oxide–semiconductor } logic. One drawback of its parameters is a high power consumption of LVPECL logic which easily reaches tens of milliamperes per device. |
| This design ensures that all system devices have access to the defined phase and known frequency. |
| 61,10 → 61,10 |
| \secc Frequency synthesis |
| We have used a centralized topology as a basis for frequency synthesis. One precise high-frequency and low-jitter digital oscillator has been used \cite[MLAB-GPSDO], while other working frequencies have been derived from it by the division of its signal. This central oscillator has a software defined GPS disciplined control loop for frequency stabilization.\fnote{SDGPSDO design has been developed in parallel to this diploma thesis as a related project, but it is not explicitly required by the thesis itself and thus it is described in a separate document} |
| We have used a centralized topology as a basis for frequency synthesis. One precise high-frequency and low-jitter digital oscillator has been used \cite[MLAB-GPSDO], while other working frequencies have been derived from it by the division of its signal. This central oscillator has a software defined GPS \glos{GPS}{Global Positioning System} disciplined control loop for frequency stabilization.\fnote{SDGPSDO design has been developed in parallel to this diploma thesis as a related project, but it is not explicitly required by the thesis itself and thus it is described in a separate document} |
| We have used new methods of software frequency monitoring and compensation in order to meet modern requirements on radioastronomy equipment which need precise frequency and phase stability over a wide baseline scales for effective radioastronomy imaging. |
| The GPSDO device consists of Si570 chip with LVPECL output. Phase jitter of GPSDO is determined mainly by Si570 phase noise. Parameters of the Si570 are summarized in the following table \ref[LO-noise] (source \cite[si570-chip] ). |
| The GPSDO device consists of Si570 chip with LVPECL output. Phase jitter of GPSDO \glos{GPSDO}{GPS disciplined oscillator} is determined mainly by Si570 phase noise. Parameters of the Si570 are summarized in the following table \ref[LO-noise] (source \cite[si570-chip] ). |
| The GPSDO design, that is included in data acquisition system, has special feature -- it generates time marks for a precise time-stamping of the received signal. Timestamps are created by disabling the local oscillator's outputs, connected to SDRX01B receivers, for 100 us. As result, a rectangular click in the ADC input signal is created which appears as a horizontal line in spectrogram. |
| Timestamps should be seen in image \ref[meteor-reflection] (above and below the meteor reflection). |
| 463,7 → 463,7 |
| \sec Parralella board computer |
| Parallella is a new product created by Adapteva, Inc. \cite[parallella-board]. It represents a small supercomputer, that has been in development for almost two years with only testing series of boards produced until now (first single-board computers with 16-core Epiphany chip were shipped in December 2013) \cite[parallella-board]. The board has nearly ideal parameters for signal processing (as it provides around 50 GFLOPS of computational power). It is is equipped with Epiphany coprocessor which has 16 High Performance RISC CPU Cores, Zynq-7020 FPGA with Dual ARM® Cortex™-A9 MPCore™ and operating frequency of 866 MHz, 1GB RAM, 85K Logic Cells, 10/100/1000 Ethernet and OpenCL support \cite[parallella16-board]. In addition to this, the board consumes only 3 Watts of power if both Zynq and Epiphany cores are running simultaniously. |
| Parallella is a new product created by Adapteva, Inc. \cite[parallella-board]. It represents a small supercomputer, that has been in development for almost two years with only testing series of boards produced until now (first single-board computers with 16-core Epiphany chip were shipped in December 2013) \cite[parallella-board]. The board has nearly ideal parameters for signal processing (as it provides around 50 GFLOPS of computational power). It is is equipped with Epiphany coprocessor which has 16 High Performance RISC CPU Cores, Zynq-7020 FPGA with Dual ARM® Cortex™-A9 MPCore™ and operating frequency of 866 MHz, 1GB RAM, 85K Logic Cells, 10/100/1000 Ethernet and OpenCL support \cite[parallella16-board]. In addition to this, the board consumes only 3 Watts of power if both Zynq and Epiphany cores are running simultaniously. |
| The main disadvantage of Parralella board is its unknown lead time and an absence of SATA interface or other interface suitable for data storage connection. Fast data storage interface would be useful and would allow bulk processing of captured data. Following that, the results of data processing may be sent over the Ethernet interface to data storage server. |
| /dokumenty/skolni/diplomka/diplomka.pdf |
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| /dokumenty/skolni/diplomka/diplomka.tex |
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| 69,6 → 69,26 |
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| /dokumenty/skolni/diplomka/introduction.tex |
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| 8,7 → 8,7 |
| As a consequence, there already exists an 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]. The radio-frequency allocation table contains special bands allocated to radioastronomy use. However, for many reasons these bands are not clean enough to be used in radioastronomy observations directly. As a result, we cannot work in the same way as did the radioastronomers in the very beginnings of radioastronomy do. Many experiments, namely Cosmic microwave background detection or pulsar detection, cannot be realised nowadays in their original forms with satisfactory results. |
| Supporting evidence of such an 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 unoccupied harsh environments like deserts, but on the other hand it simply did not meet the criteria that would make it possible to be used in modern civilisation, as we know it in Europe \cite[radio-jove]. |
| Supporting evidence of such an effect is RadioJOVE project. NASA \glos{NASA}{National Aeronautics and Space Administration} 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 unoccupied harsh environments like deserts, but on the other hand it simply did not meet the criteria that would make it possible to be used in modern civilisation, as we know it in Europe \cite[radio-jove]. |
| 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 have already seen in the light pollution mitigation pursuit, there is only a small chance to improve the situation in radiofrequency spectrum radically. |
| 20,13 → 20,13 |
| In the beginnings 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. The 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. |
| Most of the present-day operating radioastronomy equipment has been constructed in similar manner. It was produced usually shortly after the WWII or during The Cold War as a part of military technology. |
| Most of the present-day operating radioastronomy equipment has been constructed in similar manner. It was produced usually shortly after the WWII \glos{WWII}{Second World War} or during The Cold War as a part of military technology. |
| 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 new astronomical discoveries possible.\fnote{Most of astronomy-related discoveries in the last fifty years came from radioastronomy.} |
| We have the capacities necessary to develop a receiver which will have wide bandwidth, high Third-order intercept point and preferably an option for phase and frequency locking to other receivers located at another radioastronomical site at Earth. Currently there exist several receivers with the above-mentioned parameters, for example USRP2, USRP B210 or HackRF and all are commercially available. However all of them lack scalability and have high prices. It is exactly the scalability and redundancy that are the main requirements of noise reduction algorithms. |
| We have the capacities necessary to develop a receiver which will have wide bandwidth, high Third-order intercept point and preferably an option for phase and frequency locking to other receivers located at another radioastronomical site at Earth. Currently there exist several receivers with the above-mentioned parameters, for example USRP2, USRP B210 \glos{USRP}{Universal Software Radio Peripheral} or HackRF and all are commercially available. However all of them lack scalability and have high prices. It is exactly the scalability and redundancy that are the main requirements of noise reduction algorithms. |
| New radio astronomy systems such LOFAR are explicit examples of the scalability and redundancy approach. LOFAR has completely different and novel structure developed to solve the problems of radioastronomy signal reception. It exclusively uses multi antenna arrays and mathematical algorithms for signal handling. Radio signals recorded by LOFAR can be used in multiple ways: radio images can be computed (if sufficient cover of u/v plane is achieved), radiation intensity can be measured, spectrum can be analysed for velocity measurement, etc. |
| New radio astronomy systems such LOFAR \glos{LOFAR}{Low-Frequency Array} are explicit examples of the scalability and redundancy approach. LOFAR has completely different and novel structure developed to solve the problems of radioastronomy signal reception. It exclusively uses multi antenna arrays and mathematical algorithms for signal handling. Radio signals recorded by LOFAR can be used in multiple ways: radio images can be computed (if sufficient cover of u/v plane is achieved), radiation intensity can be measured, spectrum can be analysed for velocity measurement, etc. |
| \sec Required receiver parameters |
| 40,8 → 40,8 |
| \label[dynamic-range-theory] |
| Dynamic range represents a huge problem of current radioastronomical receivers. This parameter is enforced by everywhere present humans made EMI radiation on RF frequencies. The modern radio astronomy receiver must not be saturated by this high levels of signals but still needs to have enough sensitivity to see faint signals from natural sources. Dynamic range is limited either by the construction of analogue circuitry in receiver or by the digitalisation unit. |
| The maximal theoretical dynamic range of ADC could be estimated from ADC bit depth using a following formula \ref[dynamic-range] |
| Dynamic range represents a huge problem of current radioastronomical receivers. This parameter is enforced by everywhere present humans made EMI \glos{EMI}{Electromagnetic interference} radiation on RF \glos{RF}{Radio frequency} frequencies. The modern radio astronomy receiver must not be saturated by this high levels of signals but still needs to have enough sensitivity to see faint signals from natural sources. Dynamic range is limited either by the construction of analogue circuitry in receiver or by the digitalisation unit. |
| The maximal theoretical dynamic range of ADC \glos{ADC}{analog-to-digital converter} could be estimated from ADC bit depth using a following formula \ref[dynamic-range] |
| \label[dynamic-range] |
| $$ |
| 64,12 → 64,12 |
| \endinsert |
| 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 \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. But 16 bit range should be optimal as we have spare range for strongest RF signals. Two bytes sample range has in addition a good efficiency in use standard power of 2 data types length. We lock for use 16bit digital range as optimal for our design. |
| 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. But 16 bit range should be optimal as we have spare range for strongest RF signals. Two bytes sample range has in addition a good efficiency in use standard power of 2 data types length. We lock for use 16 bit digital range as optimal for our design. |
| \secc Bandwidth |
| Historically, the parameter of bandwidth in radioastronomical receiver used to be within the kilohertz range. Small bandwidth was acceptable because observations were processed directly by listening or by paper chart intensity recorder. Chart recorder integrated energy of signal over defined small bandwidth which was suitable for detecting the intensity variance of microwave background. No wide-band transmitters existed in that era (except for TV transmitters) and tuning to other neighbouring frequency was easy as they were mostly vacant. Parallel observations from several places were unnecessary as well because the electromagnetic conditions were nearly same at all locations. |
| Historically, the parameter of bandwidth in radioastronomical receiver used to be within the kilohertz range. Small bandwidth was acceptable because observations were processed directly by listening or by paper chart intensity recorder. Chart recorder integrated energy of signal over defined small bandwidth which was suitable for detecting the intensity variance of microwave background. No wide-band transmitters existed in that era (except for TV \glos{TV}{Television} transmitters) and tuning to other neighbouring frequency was easy as they were mostly vacant. Parallel observations from several places were unnecessary as well because the electromagnetic conditions were nearly same at all locations. |
| \sec State of the art receivers digitalization units |
| 77,7 → 77,7 |
| \secc Custom digitalization system |
| 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. |
| 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 \glos{ALFA}{Arecibo L-Band Feed Array} survey multi beam feed Array. |
| Another opposite example for custom receiver and digitalization unit design is LOFAR system developed by Astron in Netherlands \cite[lofar]. |
| LOFAR is innovative radioastronomy system which uses the phased antenna array approach in enormous scale and thousands (around $2 \cdot 10^4$) 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. |
| 85,19 → 85,19 |
| \midinsert |
| \clabel[lofar-antenna]{Lofar antenna configuration} |
| \picw=10cm \cinspic ./img/lofar_antenna.jpg |
| \caption/f One LOFAR LBA antenna element. |
| \caption/f One LOFAR LBA \glos{LBA}{Low Band Antenna} antenna element. |
| \endinsert |
| 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]. |
| 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 \glos{HBA}{High Band Antenna} 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 \glos{PVC}{Polyvinyl chloride} 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]. |
| \secc Modular digitalization systems |
| 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. CASPER data processing board with Z-DOK connectors is shown in picture \ref[casper-roach]. 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. |
| 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 \glos{CASPER}{Collaboration for Astronomy Signal Processing and Electronics Research} 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. CASPER data processing board with Z-DOK connectors is shown in picture \ref[casper-roach]. 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. |
| \midinsert |
| \clabel[casper-roach]{CASPER's ROACH data processing board} |
| \picw=10cm \cinspic ./img/Roach2_rev0_2xcx4mezz.jpg |
| \caption/f CASPER project ROACH-2 data processing board. White Z-DOK connectors for daughter ADC Boards can be easily seen in front. |
| \caption/f CASPER project ROACH-2 \glos{ROACH}{ Reconfigurable Open Architecture Computing Hardware (ROACH) board} data processing board. White Z-DOK connectors for daughter ADC Boards can be easily seen in front. |
| \endinsert |
| 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. |