Data Acquisition System

We would like to make radio maps using Earth-rotation aperture synthesis . This technique requires us to record raw voltages at two antennas and compute complex visibility (cross-correlation) for different frequency channels.

The block diagram of the receiver and acquisition is shown in the figure on the left.

Each of 4 antennas will have a heterodyne receiver system which will translate a signal at the radio frequency (RF) of 73.9-MHz to an intermediate frequency (IF) of 1.9 MHz.

Four such signals reach the data acquisition system marked in the diagram. Each signal will be converted to digital using a 12-bit ADC, and then sampled at the rate of 0.5 MHz using only the most significant 2-bits.

Aniket carried out feasibility studies and design of the DAS to acquire Nyquist-sampled voltages from a bandwidth-limited signal (0.25 MHz). These quantized voltages are stored on a computer disk. There is a provision of acquiring from 4 antennas, so total data rates are 0.5*4 = 2 M-samples/s. Each sample consists of 2 bits each. Hence it is 8 M-bits/s = 1 MB/s storage rate on a PC.