New Pulsar system for the 32mt dish

Involved people at OAB: D'Amico, Innocenti

The new pulsar data acquistion system was fully commissioned in 2001. This system will be used at the italian 32mt dish in Medicina to observe Pulsar radio sources. Long term timing observations of pulsars give information about the interior structure of neutron stars and is useful in the understanding of the evolution of neutron stars. In timing observations, the radio frequency signal needs to be sampled in the time and frequency domain, in order to dedisperse and detect the radio pulses. The radio frequency signal is down converted from the sky frequency of 1.4 or 1.6 GHz into 4 IF bands, each one from 16 to 48 Mhz as required by the front-end filter bank (two adjacent bands for each circular polarization). Each IF band is splitted into 32 1MHz bw channels by the filter bank, square law detected, pass-throw a programmable antialiasing filter, then digitized at 1 bit and by a fast data link built with CERN S-LINK interface; data acquired by a Pentium computer with Linux operating system will be stored on DLT tapes for off-line analysis. Time tag of data acquired is very important, so all operations are synchronized to UTC time reference by GPS receiver and sampling rate clock generator is synch to H-Maser reference.
The parameters of the data acquisition subsystem are:
$\bullet$ 2 x 64 x 1MHz filter bank (left and right polarization) designed at Jodrell Bank Observatory GB
$\bullet$ 128 channel antialiasing filter 2 poles programmable (0.9KHz, 1KHz, 5 Khz, 10Khz)
$\bullet$ 128 channel low frequency integrator (0.5 Hz) for interference monitoring system
$\bullet$ 128 channel 1 bit digitizer
$\bullet$ Synch to H-maser UT clock, programmable sampling rate (10uS-100uS)
$\bullet$ Femb board (digitizer to slink interface, Fpga xilinx based)
$\bullet$ Fast link to Personal computer By E-Slink form Nowoczesna Elektonica (LSC & LDC) & Pci to S-Link by Incaa
$\bullet$ PentiumIII-500MHz 128MB ram, Linux OS Red Hat 6.1
$\bullet$ Data storage on DLT tape unit (up to 20GB on a single tape)
$\bullet$ GPS Motorola Oncore UT+

The system has been calibrated on a number of know pulsars, using the standard timing software for offline analysis, and has shown good performances, although some issues related to the interference clipping need to be solved.

This work is carried on in collaboration with A. Maccaferri (IRA/CNR).