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\picw=15cm \cinspic ./img/SMA2SATA_nest1.JPG
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\picw=15cm \cinspic ./img/SMA2SATA_nest1.JPG
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\caption/f Balun transformer circuit used for ADC parameters measurement. It is constructed from H1012 transformer salvaged from an old Ethernet card.
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\caption/f Balun transformer circuit used for ADC parameters measurement. It is constructed from H1012 transformer salvaged from an old Ethernet card.
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\sec Example of usage
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\sec Example of usage
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At current state the constructed radioastronomy digitization unit paired with SDRX01B receiver module could be used in several experiments. We describe overall ideas of these experiments and show preliminary results in cases where we obtain the data.
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\secc Simple polarimeter station
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For additional validation of system characteristics a receiver setup has been constructed.
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If we use two antennas with different linear polarization (Crossed Yagi antennas for example), we should determine polarization state of received signal. Such kind of measurement is useful if we need an additional information about reflection to distinguish between targets. This configuration needs more complicated antenna configuration and we had no experience with this type of observation, so we have not implemented this experiment.
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\secc Basic interferometric station
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\secc Basic interferometric station
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Interferometry station was chosen to serve as the most basic experimental setup. We connected the new data acquisition system to two SDRX01B receivers. Block schematics of the setup used is shown in the image \ref[block-schematic]. Two ground-plane antennae were used and mounted outside the balcony at CTU building at location 50$^\circ$ 4' 36.102'' N,  14$^\circ$ 25' 4.170'' E.
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Interferometry station was chosen to serve as the most basic experimental setup. We connected the new data acquisition system to two SDRX01B receivers. Block schematics of the setup used is shown in the image \ref[block-schematic]. Two ground-plane antennae were used and mounted outside the balcony at CTU building at location 50$^\circ$ 4' 36.102'' N,  14$^\circ$ 25' 4.170'' E.
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Antennae were equipped with LNA01A amplifiers. All coaxial cables had the same length of 5 meters. Antennae were isolated by common mode ferrite bead mounted on cable to minimise the signal coupling between antennas. Evaluation system consisted of SDGPSDO local oscillator subsystem used to tune the local oscillator frequency.
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Antennae were equipped with LNA01A amplifiers. All coaxial cables had the same length of 5 meters. Antennae were isolated by common mode ferrite bead mounted on cable to minimise the signal coupling between antennas. Evaluation system consisted of SDGPSDO local oscillator subsystem used to tune the local oscillator frequency.
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\par\nobreak \vskip\wd0 \vskip-\ht0
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\par\nobreak \vskip\wd0 \vskip-\ht0
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\centerline {\kern\ht0 \pdfsave\pdfrotate{90}\rlap{\box0}\pdfrestore}
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\centerline {\kern\ht0 \pdfsave\pdfrotate{90}\rlap{\box0}\pdfrestore}
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\caption/f Complete receiver block schematic of dual antenna interferometric station.
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\caption/f Complete receiver block schematic of dual antenna interferometric station.
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% doplnit schema skutecne pouziteho systemu
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Despite of the schematic diagram proposed at beginning of system description \ref[expected-block-schematic].
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Despite of the schematic diagram proposed at beginning of system description \ref[expected-block-schematic].
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We have used two separate oscillators -- one oscillator drives encoded signal to ADCs still through FPGA based divider and the other one drives it to SDRX01B mixer.
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We have used two separate oscillators -- one oscillator drives ENC signal to ADCs still through FPGA based divider and the other one drives it to SDRX01B mixer.
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The reason for this modification was an attempt to simplify the frequency tuning during the experiment. A single oscillator may be used only with a proper setting of FPGA divider and this divider may be modified only by recompilation of FPGA code and loading/flashing a new FPGA schema. Due to fact that the FPGA is connected to PCI express and kernel drivers with hardware must be reinitialized, reboot of PC is required every time a FPGA scheme is changed. Instead of this complicated procedure, we set the FPGA divider to a constant division factor of 30 and used another district oscillator for ADCdual01 sampling modules and for SDRX01B receiver.
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The reason for this modification was an attempt to simplify the frequency tuning during the experiment. A single oscillator may be used only with a proper setting of FPGA divider and this divider may be modified only by recompilation of FPGA code and loading/flashing a new FPGA schema. Due to fact that the FPGA is connected to PCI express and kernel drivers with hardware must be reinitialized, reboot of PC is required every time a FPGA scheme is changed. Instead of this complicated procedure, we set the FPGA divider to a constant division factor of 30 and used another district oscillator for ADCdual01 sampling modules and for SDRX01B receiver.
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We have used ACOUNT02A MLAB instrument for frequency checking of correct setup on both local oscillators.
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We have used ACOUNT02A MLAB instrument for frequency checking of correct setup on both local oscillators.
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\midinsert
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\midinsert
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\clabel[meteor-reflection]{Meteor reflection}
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\picw=10cm \cinspic ./img/screenshots/observed_meteor.png
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\caption/f Meteor reflection received by an evaluation setup.
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\midinsert
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\clabel[phase-difference]{Phase difference}
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\clabel[phase-difference]{Phase difference}
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\picw=10cm \cinspic ./img/screenshots/phase_difference.png
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\picw=10cm \cinspic ./img/screenshots/phase_difference.png
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\caption/f Demonstration of phase difference between antennae.
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\caption/f Demonstration of phase difference between antennae.
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For the simplest demonstration of phase difference between antennae, we have analysed part of the signal by complex conjugate multiplication between channels. Results of this analysis can be seen in the following picture \ref[phase-difference]. Points of the selected part of the signal create a clear vector, which illustrates the presence of the phase difference.
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For the simplest demonstration of phase difference between antennae, we have analysed part of the signal by complex conjugate multiplication between channels. Results of this analysis can be seen in the following picture \ref[phase-difference]. Points of the selected part of the signal create a clear vector, which illustrates the presence of the constant phase difference determined by RF source direction.
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\secc Simple passive Doppler radar
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\secc Simple passive Doppler radar
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% doplnit popis
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If we use an existing transmitter with known carrier frequency and proper antenna,  we can detect flying object as signals surrounding the transmitter carrier frequency. We planned this experiment with the same station configuration as was described in section \ref[expected-block-schematic]. The ISS \glos{ISS}{International Space Station} as object and GRAVES radar transmitter were selected as adequate testing objects (We know ISS reflections from previous experiments). This experiment could be realised by previously described interferometer station,  but unfortunately we missed the suitable orbit pass due to technical lacks with station configuration.
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\secc Meteor detection station
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\secc Simple polarimeter station
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The same observational station configuration should be used for meteor detection system \cite[mlab-rmds]. We used the GRAVES radar as suitable signal source and monitored its carrier frequency. GRAVES radar is located in France therefore we could not see its direct carrier signal, but meteors reflect it signal and as consequence we could easily detect meteor presence as reflection appearance. One meteor detected by this method is shown in picture \ref[meteor-reflection].
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\midinsert
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\clabel[meteor-reflection]{Meteor reflection}
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\picw=10cm \cinspic ./img/screenshots/observed_meteor.png
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\caption/f Meteor reflection (the red spot in centre of image) received by an evaluation design.
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\endinsert
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% doplnit popis
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\chap Proposition of the final system
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\chap Proposition of the final system
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The construction of the final system, that is supposed to be employed for real radioastronomy observations will be described in this chapter. It is mainly a theoretical analysis of the data handling systems. Realization of the described ideas might be possible as a part of our future development after we fully evaluate and test the current trial design.
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The construction of the final system, that is supposed to be employed for real radioastronomy observations will be described in this chapter. It is mainly a theoretical analysis of the data handling systems. Realization of the described ideas might be possible as a part of our future development after we fully evaluate and test the current trial design.
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