| 1,8 → 1,7 |
|---|
| \chap Trial version of the receiver, design and implementation |
| |
| The whole design of radioastronomy receiver digitalization unit is constructed to be used in a wide range of applications and tasks related to digitalization of signal from radioastronomy receivers. A good illustrating problem for its use is a signal digitalisation from multiple antenna arrays. |
| The whole design of the radioastronomic receiver digitization unit is meant to be used in a wide range of applications and tasks related to digitization of a signal. A good illustrating problem for its use is the signal digitization from multiple antenna arrays. |
| |
| |
| \midinsert |
| \clabel[expected-block-schematic]{Expected system block schematic} |
| \picw=\pdfpagewidth \setbox0=\hbox{\inspic ./img/Coherent_UHF_SDR_receiver.png } |
| 13,24 → 12,26 |
|---|
| |
| \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. \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. |
| We require the following technical parameters in order to overcome the existing digitization units solutions. Primarily, we need a wide a dynamical range and a high third-order intercept point (IP3\glos{IP3}{Third-order intercept point}). The receiver must accept signals with the wide dynamics because a typical radioastronomical signal is 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 |
| |
| \medskip |
| \noindent |
| The summary of other additional required parameters: |
| % |
| \begitems |
| * Dynamical range better than 80 dB, see section \ref[dynamic-range-theory] for explanation |
| * Phase stability between channels |
| * Low noise (all types) |
| * Sampling jitter better than 100 metres |
| * Support for any number of receivers in the range of 1 to 8 |
| * Dynamic range better than 80 dB, see section \ref[dynamic-range-theory] for the explanation. |
| * Phase stability between channels. |
| * Low noise (all types). |
| * Sampling jitter better than 100 metres. |
| * Support for any number of receivers in the range of 1 to 8. |
| \enditems |
| |
| Now we analyze several of the parameters in detail. |
| \noindent |
| We analyze several of the parameters more in detail in the sequel. |
| |
| \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$\ $MSPS \glos{MSPS}{Mega-Samples Per Second} leads to the need of high end ADC chips which does not support such low sampling frequencies at all. Their minimum sampling frequency is 5$\ $MSPS. |
| The sampling frequency is not limited by the technical constrains in the trial version. This parameter is especially limited by the sampling frequencies of the analog-to-digital conversion chips available on the market and interface bandwidth. Combination of the required parameters -- dynamic range requiring at least 16bit and a minimum sampling frequency of 1$\ $MSPS \glos{MSPS}{Mega-Samples Per Second} leads to the need of high end ADC chips which does not support such low sampling frequencies at all. Their minimum sampling frequency is 5$\ $MSPS. |
| |
| We calculated a minimum data bandwidth data rate for eight receivers, 2 bytes per sample and 5$\ $MSPS as $8 \cdot 2 \cdot 5\cdot 10^6 = 80\ $MB/s. Such data rate is at the limit of the actual writing speed of classical HDD \glos{HDD}{Hard disk drive} and it is almost double the real bandwidth of USB 2.0 \glos{USB 2.0}{Universal Serial Bus version 2.0} interface. As a result of these facts we must use faster interface. Faster interface is especially needed in cases where we require faster sampling rates than ADC's minimal 5$\ $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. |
| 69,7 → 70,7 |
|---|
| 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). |
| |
| Time-marking should be improved in future by digitalization of GPS signal received by antenna on observational station. Following that, the GPS signal can be directly sampled by a dedicated receiver and one separate ADC module. Datafile then consists of samples from channels of radio-astronomy receivers along with the GPS signal containing precise time information. |
| Time-marking should be improved in future by digitization of GPS signal received by antenna on observational station. Following that, the GPS signal can be directly sampled by a dedicated receiver and one separate ADC module. Datafile then consists of samples from channels of radio-astronomy receivers along with the GPS signal containing precise time information. |
| |
| |
| \midinsert \clabel[LO-noise]{Phase noise of the local oscillator} |