Blanking Measurements

If it is desired, a blanking measurement can be made at the end of each observation and used to correct filterbank data for zero input level offsets. The length of time for this measurement is set by typing TBLANK (seconds), and the option is turned on or off by typing

BLANK FBR

use the zero check circuitry built into the filterbanks

BLANK IF

use electronic blanking in the IF circuitry

BLANK NONE

turn off all blanking measurements

There is no option to turn blanking on or off for individual filterbanks. All filterbanks use the same option. The blanking option is displayed on screen 4.

The current state of IF blanking is indicated on the millimeter electronics panel in the control room via the green "IF/BLANKING" switch/light combination. When the "BLANKING" half is lit, blanking is in effect. This may occur in three ways: IMPORTANT!! As of the 1993 observing season, the Blanking option should be set to NONE. Blanking is recorded on a monthly basis by the staff.

1. If the switch/light combination has been pressed such that manual blanking overrides anything the computer may be attempting to do (just press the switch again to get back into computer control).
2. Someone has used the BLON keyword to turn on the blanking via software. Type BLOFF to turn it off.
3. Someone is taking data using the blanking option and the blanking measurement is under way. Unless the scan is aborted at the wrong time, the blanking will turn off automatically.

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Table 3.6

Spectrometer Keywords

SPEC

Select spectral line observing mode

CONF (ID F$_n$ F$_n$ ...)

Put desired filterbanks into configuration ID.

CBAND (nMHZ)

where nMHZ=2.5,5,10,20,40,80. Selects the bandwidth of FAAS

CPIX (pixel)

disables a malfunctioning pixel in the

CMAIN

attenuates IF level in the main buffer of the correlator

CREF

attenuates IF level in the ref buffer of the correlator.

CSMOOTH (n)

where n=0 to 7 selects the weighing option to the ACF prior to the FFT.

CTHRESHOLD

sets IF level fed into the correlator.

BADC (F$_n$) (ON or OFF)

Turn ON or OFF the bad channels listed on screen 3 for filterbank F$_n$

CHAD (F$_n$) (x,x, or x to x)

Add channel number x or (x to x) to bad channel list for filterbank F$_n$

CHDEL (F$_n$) (x,x, or x to x or ALL)

Remove from the bad channel list for filterbank F$_n$ channels x, or (x to x) or all channels currently listed on screen 3

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

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