## Receiver setup

The receiver tuning is selected by the LINE command, which has the same syntax as the corresponding command in the OBS software on Plateau de Bure:

LINE name frequency band lock center harm /RECEIVER_BAND irec

name is a line name, only used to label the plot; frequency is the rest frequency in GHz; band should be USB or LSB; lock is LOW or HIGH [optional, default LOW]; center is the IF1 frequency (in MHz) that must correspond to the required rest frequency [optional, default 6500]; harm is the harmonic number [optional, reserved for experts]. The /RECEIVER_BAND option is optional, the software will automatically find the appropriate receiver band, depending on the rest frequency.

It is highly recommended not to center the line at 6 GHz. This is because the correlator will analyse four 1 GHz-wide slices of the 4 GHz bandwidths, and 6 GHz is very precisely at the limit between two such adjacents quarters (see below).

The LINE command produces a plot of both the LSB and USB frequency coverage (the non-selected band being in light grey). The four quarters that are analyzed by the IF/correlator system are indicated by horizontal arrows (see Fig. ). Vertical lines indicate the positions of the main molecular lines.

Figure: Plateau de Bure frequency coverage: ouptut of LINE test 100 LSB. Both the LSB and USB frequency coverages are displaye.

Figure: Plateau de Bure frequency coverage: ouptut of LINE; NARROW; SPECTRAL commands.