Turn the noise-calibration signal on or off.

Arguments:

SwitchState state

The desired state of the noise source on or off.

Example 1:

The following example turns the noise-cal signal on for 10 seconds.

 noise_cal on
 until $elapsed > 10s
 noise_cal off

Context:

To calibrate the response of the CBI correlator to a signal being presented to a given antenna of the CBI, a stable noise source is injected into the receiver signal path and compared to the signal received from an astronomical calibration source. During normal observing, signals coming from random sources on the sky can then be compared against the noise source to ascertain their flux. This requires that one be able to switch the noise source into the signal path periodically. The noise source actually remains switched on all of the time, but it is usually disconnected from the receiver inputs by switches. There is one master switch on the output of the noise generator followed by 13 individual switches that connect the noise source to each receiver. So with all of these switches open, there are two switches between each receiver and the noise source. This ensures sufficient isolation between the noise source and the receivers. The noise_cal command switches all of these switches either on or off. To switch them individually, use the setreg command to write directly to the noise_dio.output register. The first 13 bits, spread between the first 2 bytes of this register, control the individual switches. The 14th bit controls the master switch.