Multibeam Receiver Setup
The Parkes 21cm Multibeam Receiver consists of a 13-beam cooled 20cm receiver system, located at the prime focus of the 64m dish. The hexagonal feed cluster is designed by the CSIRO Division of Telecommunications and Industrial Physics.
Signals from 26 channels (note 2 polarizations) are down-converted and sent to the pulsar Multibeam filterbank system in the control room. This provides 2 x 96 x 3 MHz channels for each beam. Signals from the centre beam are tapped off and can be sent to other filterbank systems or the Caltech correlator. For pulsar observations, the 1st LO is normally set to 1582 MHz. There is a doubler in the focus cabin, so the reference frequency (normally set on the Rohde & Schwarz signal generator in Rack 5) is 791 MHz; the level is +11 dBm.
IF signals for the 13 beams and polarizations A and B come from the focus cabin to the Multibeam Cable Equalizer in Rack G. This corrects for the frequency-dependent cable loss and provides level setting in 1 db steps separately for each beam and polarization. It also splits off the signals for the Multibeam correlator. See Multibeam pulsar system for a block diagram of the system.
The Multibeam filterbank system accepts IFs in the range 1230 - 1518 MHz (total bandwidth 288 MHz for each polarization). Each beam and polarization is split into three subbands, each of which is downconverted to 64 - 160 MHz for input to the filterbank modules by the Multibeam up-down converter and band-splitter. This requires three LOs from the Multibeam LO module. Frequency Relations.
The 78 cables from the band-splitters go to the filterbanks in Racks E and F. Connections at the rear of each filterbank are shown in Filterbank Assignments. Ribbon cables take the filterbank outputs to the digitizer (see below). Sockets on the rear of the filterbanks are in parallel pairs, that is, sockets 1 and 2 of Crate A both have the polarization-summed outputs from the lowest subband (centred at 112 MHz) of beam 1. Each ribbon cable carries 32 signals to the digitizer.