Signal processing in the field

Each receiver unit accepts the analog data streams from 8 MWA tiles over coaxial cable, and outputs digital data streams on optical fibre. To do this, it digitizes the input RF signal after appropriate signal conditioning, and passes the data through a coarse polyphase filter to obtain 1.28 MHz wide "coarse" channels. Astronomers can then select 24 of these coarse channels (within the total tile bandwidth of 70-300MHz) for transmission, giving the MWA a total instantaneous bandwidth of 30.72MHz.

The receiver contains additional components including a sampling clock module and Monitor & Control (M&C) capability to control the digital and analog hardware. The M&C subsystem sends and monitors beam-steering commands and monitors environmental parameters and system health. The receiver enclosure is weather tight, protected against lightning and RFI-tight to avoid significant spurious emissions.

The principal components associated with the receiver are shown in the schematic in Figure 3.

Figure 1: Two MWA receivers side-by-side in the field

For maximum linearity of response, the MWA uses a direct RF sampling receiver architecture. The receiver consists of all components between the RF output of the analog antenna tile beamformer, and a high spectral resolution digital data stream transmitted to the central processing facility. In this case, the "F" part of the "FX" correlator architecture becomes part of the receiver, in conjunction with the fine polyphase filterbank at the correlator.

Figure 2: Inside a receiver

Figure 3: A top-level diagram of the receiver system

Figure 4: A receiver configured for long baseline tiles