Continuum Configurations

To make continuum observations, it is necessary to enter into continuum observing mode with the CONT command and to select which continuum backend to process the information. There are four choices for the continuum backends:

DVM

In this configuration, the panel dvm is used as the source of continuum data.

VSYNCH

In this configuration, the 2 channel continuum V/F is used to collect data in a beam chopping mode. This is not presently implemented for array receivers.

VTOF

In this configuration, the 2 channel continuum V/F is used to collect data in a mode analogous to the DVM mode.

FILT

SEQUOIA only. In this configuration, the sky contribution is determined from a reference pixel in the array which is set by the RPIX command.

CPOL

In this configuration, the polarizer (assumed to be in line) is rotated, and the first channel of the continuum V/F is used to collect data.

The continuum modes DVM and CPOL provide only 1 channel of information for data storage. The VTOF and VSYNCH modes provide 2 channels of data. In a stored data scan these two channels are accessed as a first and second backend. Because the maximum number of data points that can be stored in a scan is 1024, each of these 2 backends can have a maximum of 512 data points. The VSYNCH mode requires that the beam chopper be running. The message "BAD CONTINUUM V/F DUMP DELETED" on the TEK4023 during VTOF , CPOL , or VSYNCH continuum observations indicates a hardware problem in the continuum V/F equipment.

For SEQUOIA, the continuum mode FILT uses a reference pixel to determine the sky contribution to the observed signal. This reference emission is subtracted from all remaining pixels. The reference pixel is defined by the RPIX command. For example, in order to define pixel 5 as the reference pixel to be used in FILT mode, the user type
RPIX 5.
In most cases, a corner pixel (i.e. pixel 1, 4, 13, or 16) is used as the reference pixel. This mode is used for telescope pointing on continuum point sources such as a planet. In order to not use a reference pixel, the user types
RPIX 0

truein

Table 3.7

Backend Continuum Keywords

CONT

Select continuum observing mode

BLANK (FBR, IF, or NONE)

Set blanking option used to correct filterbank data for zero input level offsets

TBLANK (seconds)

Length of time (seconds) for blanking measurement - typically 1-3 seconds

BLON

Special software test command to turn on continuous blanking

BLOFF

Turn off BLON command

DVM

Select panel DVM for continuum observation

FILT

Select filter bank mode for continuum observation. SEQUOIA only.

RPIX (integer (0-16)

Select reference pixel for FILT mode continuum observation. SEQUOIA only.

VTOF

Select 2 channel V/F for continuum observation

VSYNCH

Select 2 channel V/F plus beam chopper for continuum observations

CPOL

Rotate polarizer while using 2 channel V/F for continuum observations

truein