Hardware Overview
Frontend System
The front end system (Figure 1) consists of a broadband (1-18 GHz) dual-polarization log-periodic crossed-dipole feed, and a thermally-controlled RF box (called the FEM, or Front End Module) that houses the amplifiers, calibration noise source (noise diode), attenuators, and optical transmitters needed to control the gain of the system and supply the two RF signals multiplexed onto a single optical fiber output.
The block diagram for the FEM is shown in Figure 2.
Downconverter System
Digital Correlator
Equalizer Coefficients
Each ROACH has a set of four registers named 'eq_x0_coeffs', 'eq_x1_coeffs', 'eq_x2_coeffs', and 'eq_x3_coeffs'.