New correlator MicroPARSEC Igor Surkis, Vladimir Zimovsky, Violetta Shantyr, Alexey Melnikov Institute of Applied Astronomy Russian Academy of Science

The Institute of Applied Astronomy has developed the new VSI-H hardware correlator MicroPARSEC in the recent years. The MicroPARSEC unit is based on the Altera FPGA technology. This correlator has been developed as standard PCI board to be set in a personal computer. MicroPARSEC was used to process VLBI observations on the three-station Russian VLBI network Quasar. It also was used to proceed spectral observations and to test the equipment of Quasar stations. Abstract

The main goal of the MicroPARSEC project is to provide Russian national VLBI network Quasar with modern correlation processing instrument. MicroPARSEC correlator was developed in in the IAA RAS. First MicroPARSEC units were produced in the middle of In the middle of 2005 release version of the control software and FPGA chip program was completed. MicroPARSEC becomes the main correlator in the Russian VLBI network Quasar in the middle of 2005.

The MicroPARSEC unit designed as the PCI standard plate. It can be installed into the standard PC-based computer. The MicroPARSEC requires VSI-H input data stream. At the, moment it works with a S2-PT unit. We are going to use hard disk playback systems such as Mark 5B. The MicroPARSEC unit is designed on the Altera FPGA technology.

MicroPARSEC unit 6 Altera FPGA chips 4 RAM chips PCI controller chip.

Each MicroPARSEC unit includes 2 VLBI correlator blocks. Each block is a complex XF correlator to process correlation from one frequency channel of one base. The MicroPARSEC unit is directly connected to a S2-PT device by the standard cable. Each correlator block input can be connected with any of 16 S2-PT outputs with the special switcher in the MicroPARSEC.

Correlation block scheme Input decoder to set the modes and the levels of the input signals The module with two 128 Mb RAM chips to compensate signal delay at the baseline; it can work in the baseline or the station mode. The phase generator and mixer module to compensate fringe rate; it can mix signals from the first or the second station. The correlator module to obtain correlation function The Phase-Cal processing module for baseline stations

Features of the MicroPARSEC correlator block: 64 complex lags on output Cal complex signals of the two stations on output 2-bit or 1-bit sampling, Sign, Magnitude and Valid input from each station the clock rate is up to 32 MHz integration time 5 ms – 10 sec VSI-H input data stream: unformatted data stream, clock rate, 1 Hz strobe

Correlator with one S2-PT unit and one MicroPARSEC unit One MicroPARSEC unit One S2-PT unit The control computer The software to control the MicroPARSEC unit (through PCI bus) and S2-PT (through telnet)

Correlator with one S2-PT unit and four MicroPARSEC units Set of MicroPARSEC units is used to increase the number of frequency channels processed simultaneously. Now the four MicroPARSEC correlator is used in IAA RAS. MicroPARSEC units are inserted in one computer and receive the S2-PT data stream through the special commutation unit. The correlator process 8 frequency channels of one baseline.

Correlator with four MicroPARSEC units

Our plans are to equip correlator with 12 MicroPARSEC units and 2 S2-PT units. It allows us to process up to 24 frequency channels in different combinations.

The special software under Microsoft Windows 98 on the correlation computer controls MicroPARSEC units. The software performs the following tasks: To control MicroPARSEC units installed on the computer To control S2-PT through telnet protocol To display correlation results of selected frequency channel in real time To save the results for further processing

VLBI software screenshot

Application of the MicroPARSEC correlator Stations coordinates 3 cm UT1-UTC 0.1 millisecond Celestial pole coordinates 3 mas Earth pole coordinates 8 mas The VLBI observations on the Russian VLBI network Quasar (stations Svetloe, Zelechyckskaya, Badary) were performed in November-December of Four 2 MHz channels in X-band were registered, maximum frequency range between channels was 150 MHz. 1-bit sampling was used. The goal of the observations was to test all the equipment and to obtain EOP. Four MicroPARSEC units correlator was used to process these observations. After the fringe fitting procedure the multiband group delays were obtained. The accuracy of the delays achieve picoseconds, which is in good agreement with expected accuracy. Achieved accuracy of the station coordinates and EOP:

Using MicroPARSEC unit as a spectrum analyser The single MicroPARSEC unit can be used as a spectrum analyser. In this case it can be used at the station, and connected directly to the sampling device output. The MicroPARSEC unit calculates the autocorrelation function, and the correlation computer performs the Fourier transformation. One MicroPARSEC unit can produce function with 256 points directly. If the signal is stationary we can make the autocorrelation function longer by correlating different parts of it in different time. During experiments on the Svetloe station we obtained the autocorrelation function of points. The spectrum has 8192 points. In the 2 MHz channel we obtained resolution of 250 Hz.

Spectrum analyser software screenshot Observed W3OH on 18 cm, station Svetloe.

MicroPARSEC summary VLBI complex XF correlator; can work as a spectrum analyser Two frequency channels on one unit 64 complex lags of each channel on output Cal complex signals of the two stations of each channel on output 2-bit or 1-bit sampling, Sign, Magnitude and Valid input from each station each channel the clock rate is up to 32 MHz integration time 5 ms – 10 sec VSI-H input data stream: unformatted data stream, clock rate, 1 Hz strobe

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