Medicina Correlator

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Contents

Summary

The Medicina correlator is a CASPER packetised correlator operating on 8 cylinders of the Northern Cross's NS arm.

It has 32 single polarisation inputs and processes 40MHz bandwidth (usable 16MHz) centered at sky frequency 408MHz at an IF of 40MHz, oversampled at 160MHz. As at 01 October 2008 it was using X_rev309c and F_rev303.

This page details installation and configuration procedures.

Array Details

Numbering convention

NC reference pnt detail.jpg

The following table details numbering convention and current interconnect.

Correlator internal - external mapping showing physical connections

                                    phy     DP      SP      PHY         location relative to ref pos.
ADC             IBOB    BEE_fpga    XAUI    ANT     ANT     INPUT       in wavelengths at 408MHz
===============================================================================================    
bottom I        0       0           0       0x      0       1N-1-3      6.804708,-18.8875321,0
bottom Q        0       0           0       0y      1       1N-1-4      6.804708,-10.8875321,0
top I           0       0           0       1x      2       1N-1-1      6.804708,-34.8875321,0
top Q           0       0           0       1y      3       1N-1-2      6.804708,-26.8875321,0
------------------------------------------------------------------------------------------------
bottom I        1       1           0       2x      4       1N-2-3      20.414123,-18.8875321,0
bottom Q        1       1           0       2y      5       1N-2-4      20.414123,-10.8875321,0
top I           1       1           0       3x      6       1N-2-1      20.414123,-34.8875321,0
top Q           1       1           0       3y      7       1N-2-2      20.414123,-26.8875321,0
------------------------------------------------------------------------------------------------
bottom I        2       2           0       4x      8       1N-3-3      34.023538,-18.8875321,0
bottom Q        2       2           0       4y      9       1N-3-4      34.023538,-10.8875321,0
top I           2       2           0       5x      10      1N-3-1      34.023538,-34.8875321,0
top Q           2       2           0       5y      11      1N-3-2      34.023538,-26.8875321,0
------------------------------------------------------------------------------------------------
bottom I        3       3           0       6x      12      1N-4-3      47.632953,-18.8875321,0
bottom Q        3       3           0       6y      13      1N-4-4      47.632953,-10.8875321,0
top I           3       3           0       7x      14      1N-4-1      47.632953,-34.8875321,0
top Q           3       3           0       7y      15      1N-4-2      47.632953,-26.8875321,0
------------------------------------------------------------------------------------------------
bottom I        4       0           1       8x      16      1N-5-3      61.242368,-18.8875321,0
bottom Q        4       0           1       8y      17      1N-5-4      61.242368,-10.8875321,0
top I           4       0           1       9x      18      1N-5-1      61.242368,-34.8875321,0
top Q           4       0           1       9y      19      1N-5-2      61.242368,-26.8875321,0
-----------------------------------------------------------------------------------------------
bottom I        5       1           1       10x     20      1N-6-3      74.851783,-18.8875321,0
bottom Q        5       1           1       11y     21      1N-6-4      74.851783,-10.8875321,0
top I           5       1           1       12x     22      1N-6-1      74.851783,-34.8875321,0
top Q           5       1           1       13y     23      1N-6-2      74.851783,-26.8875321,0
-----------------------------------------------------------------------------------------------
bottom I        6       2           1       14x     24      1N-7-3      88.461198,-18.8875321,0
bottom Q        6       2           1       14y     25      1N-7-4      88.461198,-10.8875321,0
top I           6       2           1       15x     26      1N-7-1      88.461198,-34.8875321,0
top Q           6       2           1       15y     27      1N-7-2      88.461198,-26.8875321,0
------------------------------------------------------------------------------------------------
bottom I        7       3           1       16x     28      1N-8-3      102.070613,-18.8875321,0
bottom Q        7       3           1       16y     29      1N-8-4      102.070613,-10.8875321,0
top I           7       3           1       17x     30      1N-8-1      102.070613,-34.8875321,0
top Q           7       3           1       17y     31      1N-8-2      102.070613,-26.8875321,0
================================================================================================

On each IBOB, the bottom ADC corresponds to ADC0. The top ADC is ADC1.

Each ADC has two inputs, labelled I and Q on the PCB. 'I' is on top, 'Q' is on the bottom. I corresponds to 'X' or North-South polarisation and Q 'Y' or East-West polarisation on a dual-pol design.

All of Medicina's NS arm has east-west, or 'Y' polarisation.

The meeting of the EW and NS arms is at location = 44:31:24.88, 11:38:45.56. Height above sea level ±50m. This is the reference point for all antenna locations. It is in the center of the EW-arm, and in between two NS-arm cylinders.

Each cylinder in the N-S arm is located 10m apart (13.609415 wavelengths at 408MHz).

Cylinders are numbered in groups of 8. Group 1 (the only one in use by the correlator at the moment) has its southern most cylinder just north of the reference point.

Each cylinder in the group is numbered South to North starting at 1.

Each cylinder is equipped with four receivers located 8.0 wavelengths apart (at 408MHz) (±5m) E-W.

Recievers on the cylinders are numbered 1 through 4, with one being on the west and four being at the east.

Receivers are numbered AB-C-D, where A is the group B is the arm (in this case always 'N' for NS arm) C is the cylinder number within the group (1 through 8) D is the receiver on the cylinder (1 through 4)

Hardware

The hardware consists of 8 IBOBs, 16 2GSs/s ADCs and one BEE2.

Results

We were able to design, configure and install the system and obtain our first image of Cassiopeia within 10 days. The following pictures show the image formed from 1 hour of captured data.

Notice the strong RFI in this waterfall plot of baseline 1-2.
Amplitude plot of Baseline 1-2

This plot shows the phase of baseline 1-2 after RFI has been excised.
Phase plot of baseline 1-2 after removing RFI

This is the deconvolved image. AIPY's CLEAN algorithm was used.
AIPY CLEAN deconvolved image

Zooming-in on the cleaned image shows that most of the source was correctly resolved to the center pixel. The images are mostly due to the poor resolution (only four receivers in the E-W direction, with equal spacing). Making use of the E-W arm of the Northern Cross will solve this.
Deconvolve zoom

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