The Wideband Correlator PolyFiX

The wide-band correlator PolyFiX can process a total instantaneous bandwidth of $\sim$ 31 GHz for up to twelve antennas that is split into two polarisations in each of the two available sidebands (the upper and lower sideband). The centers of the two 7.744 GHz wide sidebands are separated by 15.488 GHz. Each sideband is composed of two adjacent basebands of $\sim$3.9 GHz width, called inner and outer baseband (see Fig. 1). In total, there are thus eight basebands which are fed into the correlator. The channel spacing is 2 MHz² throughout the 15.488 GHz effective bandwidth per polarization. Additionally, up to sixteen high-resolution chunks can be selected in each of the eight basebands (i.e. up to 128 chunks in total). Each of these has a width of 64 MHz and, in the current implementation step of PolyFiX, a fixed channel spacing of 62.5 kHz. A number of contiguous chunks defines one spectral window (SPW).

Please note that there is a “non-exploitable, 20 MHz wide frequency area” ($\equiv$ LO2 zone) around the center of each sideband, i.e., in between the inner and outer basebands. Due to the filter response of the correlator, the noise level is also increased by up to a factor of two within a width of $\pm$50 MHz around the center in each sideband. Important lines should therefore not be placed in this region (see also pages 19 and 20 in this PolyFiX tutorial).

Subsection explains how to configure the correlator using the GILDAS package ASTRO.

Figure: Basebands fed to the correlator