Цифровые видеоконверторы для радиоастрономических систем преобразования сигналов

The digital down converters can be used on the radio telescopes with small antennas which are equipped with digital data acquisition  systems with bands Bs = 512 MHz. The down converters provide  extracts a number of signals with bands AF = 16 or 8 MHz at  specified frequencies from the digital sequence of samples of a  wideband signal with the frequency fd = 1024 MHz, 4-level  quantization and formatting of the extracted signals according to the international standard VDIF that used in radiointerferometry. This is  necessary to connect a radio telescope with broadband data  acquisition systems (for example, RT-13) to international radio  interferometry networks (VLBI), which use systems with narrowband (up to 16 MHz) signals. The developed module is made on the basis  of the programmable logic integrated circuit (FPGA) XC7K325T and  provide extracts and formats up to 16 narrowband (16 or 8 MHz) signals from three digital broadband signals that received from the  broadband channels of the radio telescope via fiber optic lines by the 10 gigabit ethernet. The resulting data stream is sent to the buffering device for subsequent transmission to the VLBI correlator. The digital down converters operating at a clock frequency fm = 128  MHz, allow to extract signals in band Bc = 64 MHz and are tuned  with 10 kHz steps by digital oscillator synthesizers. The Bs band of input signal are splitted by 8 channels using 8-channel polyphase filters, which reduce the clock frequencies by eight times. The  module provides the same mode of signal extraction and formatting,  which is widely used in VLBI networks with astrometric and geodetic observations in two wave bands.Цифровые видеоконверторы предназначены для систем преобразования сигналов радиотелескопов. Для видеоконвертора, работающего с тактовой частотой 128 МГц,  характерной для радиоастрономической аппаратуры на программируемых логических  интегральных схемах, разработан цифровой гетеродин с шагом перестройки 10 кГц. Блок,  содержащий 16 цифровых видеоконверторов, выделяет сигналы с полосой 16 или 8 МГц из  потоков данных 10GE, поступающих от каналов преобразования широкополосных (512 МГц) сигналов

Сравнение радиоинтерферометров с аналоговыми и цифровыми системами выделения регистрируемых сигналов

Introduction. Radio telescopes of Very Long Baseline Interferometry (VLBI) networks usually record several signals with relatively narrow (up to 32 MHz) bands, which are extracted by means of base band converters (BBC) from an analog noise signal of an intermediate frequency (IF) with bands up to 1 GHz. When processing data, frequency band synthesis is used. At new small radio telescopes (for example, RT-13), directly wideband IF signals are digitized. An ability to connect the RT-13 radio telescope to the “Quasar” VLBI complex and to international VLBI networks provides by a digital narrow-band signal extraction module developed in 2019.Aim. Determining the measuring accuracy of an interferometric group delay of a signal by a radio interferometer with a digital narrow-band signal extraction module and comparing the sensitivity of interferometers with analog and digital signal extraction systems.Materials and methods. Sensitivity losses of interferometers with different systems for detecting recorded signals were calculated. The accuracy of a multi-channel interferometer with the synthesis of a frequency band and of an interferometer with recording of digital broadband IF signals without band synthesis was compared. The results were confirmed by VLBI observations in the observatories of the “Quasar” complex.Results. When replacing the analog system of signal extraction with digital system the sensitivity losses of the interferometer were slightly reduced. The measurement accuracy of the interferometric group delay had not changed. Accuracy increased when digitally recording broadband IF signals and when synthesizing a frequency band significantly larger than the IF bandwidth. Conditions and minimum synthesized bands were determined under which the accuracy of the interferometer with the registration of narrowband signals can be higher than the accuracy of the interferometer with the registration of wideband IF signals.Conclusion. The problem of combining RT-13 radio telescopes with VLBI networks with recording of video frequency signals was solved. The efficiency of the installation of digital signal conversion systems at radio telescopes was shown.Введение. Радиотелескопами комплексов радиоинтерферометрии со сверхдлинными базами (РСДБ) обычно регистрируются несколько сигналов с относительно узкими (до 32 МГц) полосами, которые выделяются видеоконверторами из аналогового шумового сигнала промежуточной частоты (ПЧ) с полосами до 1 ГГц. При обработке данных применяется синтез полосы частот. На новых небольших радиотелескопах (например, РТ-13) оцифровываются широкополосные сигналы ПЧ. Возможность подключения радиотелескопа РТ-13 к РСДБ-комплексу "Квазар-КВО" и к международным РСДБ-сетям обеспечивает модуль цифрового выделения узкополосных сигналов, разработанный в 2019 г.Цель работы. Определение точности измерения интерферометрической групповой задержки сигнала радиоинтерферометром с цифровым модулем выделения регистрируемых сигналов и сравнение чувствительностей интерферометров с аналоговыми и с цифровыми системами выделения сигналов.Материалы и методы. Рассчитываются потери чувствительности интерферометров с разными системами выделения регистрируемых сигналов. Сравниваются точности многоканального интерферометра с синтезом полосы частот и интерферометра, регистрирующего цифровые широкополосные сигналы ПЧ без синтеза полосы. Результаты подтверждаются РСДБ-наблюдениями в обсерваториях комплекса "Квазар-КВО".Результаты. При замене аналоговой системы выделения сигналов на цифровую потери чувствительности интерферометра немного снижаются. Точность измерения интерферометрической групповой задержки не меняется. Точность повышается при синтезе полосы частот, значительно превышающей ширину полосы ПЧ, и при цифровой регистрации широкополосных сигналов ПЧ. Определены условия и минимальные синтезируемые полосы, при которых точность интерферометра с регистрацией узкополосных сигналов может быть выше точности интерферометра с регистрацией широкополосных сигналов ПЧ.Заключение. Решена задача совмещения радиотелескопов РТ-13 с РСДБ-сетями, где регистрируются сигналы видеочастот. Показана эффективность установки на радиотелескопах цифровых систем преобразования сигналов

Измерение параметров сигналов в широкополосных приемно-регистрирующих каналах радиотелескопа

The built-in system of parameter measurement for wideband (up to 512 MHz) receiving and recording channel of radio interferometer is considered. The estimation of measurement accuracy and the precision alignment of group delays in the receiving channel are investigated. In addition, this system provides the control of receiving channel frequency response and phase response functions.Рассмотрена встроенная система измерения параметров широкополосного (до 512 МГц) сигнала в приемно-регистрирующем канале радиоинтерферометра. Дана оценка точности измерений групповых задержек сигналов в приемных каналах интерферометра. Показана возможность контроля фазочастотной и амплитудно-частотной характеристик приемного канала

The Digital Down Converters for a Radio Astronomy Data Acquisition Systems

The digital down converters can be used on the radio telescopes with small antennas which are equipped with digital data acquisition  systems with bands Bs = 512 MHz. The down converters provide  extracts a number of signals with bands AF = 16 or 8 MHz at  specified frequencies from the digital sequence of samples of a  wideband signal with the frequency fd = 1024 MHz, 4-level  quantization and formatting of the extracted signals according to the international standard VDIF that used in radiointerferometry. This is  necessary to connect a radio telescope with broadband data  acquisition systems (for example, RT-13) to international radio  interferometry networks (VLBI), which use systems with narrowband (up to 16 MHz) signals. The developed module is made on the basis  of the programmable logic integrated circuit (FPGA) XC7K325T and  provide extracts and formats up to 16 narrowband (16 or 8 MHz) signals from three digital broadband signals that received from the  broadband channels of the radio telescope via fiber optic lines by the 10 gigabit ethernet. The resulting data stream is sent to the buffering device for subsequent transmission to the VLBI correlator. The digital down converters operating at a clock frequency fm = 128  MHz, allow to extract signals in band Bc = 64 MHz and are tuned  with 10 kHz steps by digital oscillator synthesizers. The Bs band of input signal are splitted by 8 channels using 8-channel polyphase filters, which reduce the clock frequencies by eight times. The  module provides the same mode of signal extraction and formatting,  which is widely used in VLBI networks with astrometric and geodetic observations in two wave bands

Comparison of Radio Interferometers with Analog and Digital Extraction of Recorded Signal

Introduction. Radio telescopes of Very Long Baseline Interferometry (VLBI) networks usually record several signals with relatively narrow (up to 32 MHz) bands, which are extracted by means of base band converters (BBC) from an analog noise signal of an intermediate frequency (IF) with bands up to 1 GHz. When processing data, frequency band synthesis is used. At new small radio telescopes (for example, RT-13), directly wideband IF signals are digitized. An ability to connect the RT-13 radio telescope to the “Quasar” VLBI complex and to international VLBI networks provides by a digital narrow-band signal extraction module developed in 2019.Aim. Determining the measuring accuracy of an interferometric group delay of a signal by a radio interferometer with a digital narrow-band signal extraction module and comparing the sensitivity of interferometers with analog and digital signal extraction systems.Materials and methods. Sensitivity losses of interferometers with different systems for detecting recorded signals were calculated. The accuracy of a multi-channel interferometer with the synthesis of a frequency band and of an interferometer with recording of digital broadband IF signals without band synthesis was compared. The results were confirmed by VLBI observations in the observatories of the “Quasar” complex.Results. When replacing the analog system of signal extraction with digital system the sensitivity losses of the interferometer were slightly reduced. The measurement accuracy of the interferometric group delay had not changed. Accuracy increased when digitally recording broadband IF signals and when synthesizing a frequency band significantly larger than the IF bandwidth. Conditions and minimum synthesized bands were determined under which the accuracy of the interferometer with the registration of narrowband signals can be higher than the accuracy of the interferometer with the registration of wideband IF signals.Conclusion. The problem of combining RT-13 radio telescopes with VLBI networks with recording of video frequency signals was solved. The efficiency of the installation of digital signal conversion systems at radio telescopes was shown

Measuring signal parameters in wideband receiving and recording channels

The built-in system of parameter measurement for wideband (up to 512 MHz) receiving and recording channel of radio interferometer is considered. The estimation of measurement accuracy and the precision alignment of group delays in the receiving channel are investigated. In addition, this system provides the control of receiving channel frequency response and phase response functions