## Correlator setup

The details of the IF processor and narrow-band correlator frequency plan is presented in another document. In short: the input 4–8 GHz band is split by the IF processor in four 1 GHz parts, labeled Q1, Q2, Q3, Q4. This processing is done in parallel for both polarizations. Since the narrow-band correlator accepts only two 1 GHz input signals, one has to define which part (=which quarter of which polarization) of the signal is to be sent to the correlator. The system allows the following choices:

- first correlator input can only be Q1 HOR, Q2 HOR, Q3 VER, or Q4 VER
- second correlator input can only be Q1 VER, Q2 VER, Q3 HOR, or Q4 HOR

where HOR and VER refers to the two polarizations and Q1...Q4 to the four quarters of the input 4 GHz signal. Note, that these quarters are 1 GHz wide but are covering only 3.6 GHz in total (due to filters' edges), hence an overlap between Q1 and Q2 on one side, and Q3 and Q4 an the other side:

Q1 = 4.2–5.2 GHz
Q2 = 5.0–6.0 GHz
Q3 = 6.0–7.0 GHz
Q4=6.8–7.8 GHz.

The command

NARROW_INPUT Q1|Q2|Q3|Q4 Q1|Q2|Q3|Q4

allows one to select the two entries of the narrow-band correlator. The polarization is determined from the above list. For instance, NARROW_INPUT Q1 Q2 selects Q1 as the first correlator entry – this can only be Q1 HORizontal– and Q2 as the second correlator entry – this can only be Q2 VERtical. Selecting two times the same quarter (e.g. NARROW Q2 Q2) results in both polarization being observed simultaneously, in the same frequency range.

NARROW_INPUT produces a new plot, where the frequency coverage of the two selected quarters are displayed. After that step, the SPECTRAL command is used to defined and plot the positions and widths of each of the 8 units of the correlator. The syntax is:

SPECTRAL iunit bandwidth fcenter /NARROW 1|2

where:

- iunit is the correlator unit number (1 to 8);
- bandwidth is the bandwidth in MHz (20, 40, 80, 160, or 320);
- fcenter is the center frequency (in MHz) of the unit in the second IF (in the range 100 to 1100 MHz);
- the option /NARROW is mandatory, to select which entry of the correlator the unit is connected to.

Example – Figure presents the plot produced by the command sequence:

      LINE test 100 LSB
      NARROW Q3 Q4
      SPECTRAL 1  80  550 /NARROW 1
      SPECTRAL 2  80  350 /NARROW 1
      SPECTRAL 3  20  793 /NARROW 1
      SPECTRAL 4  20  700 /NARROW 1
      SPECTRAL 5 320  360 /NARROW 1
      SPECTRAL 6 320  740 /NARROW 1
      SPECTRAL 7 320  540 /NARROW 1
      SPECTRAL 8 320  830 /NARROW 1