User's Manual for B3 Tuning Instructions

An "I-Task" controls receiver B3 from the VAX. In the following list of commands user input is shown in bold face. Choices are separated with a vertical bar "|"; for example, "A | B" means "enter either A or B". As always, ICL commands are not case-sensitive.

Standard startup for B3

Issue the frontend (given as fe] under ICL) command.

This is used to select and configure B3. In addition to requiring inputs for frequency, velocity and velocity frame, the options for B3 are:

• POLARITY (Single | Dual) - i.e. use one or both polarization channels
• CHANNEL (1 | 2) - i.e. if polarity = Single, specify either channel 1 or channel 2 (equivalent to "A" or "B")
• SIDEBAND MODE (SSB | DSB) - set the sideband filter for single sideband (SSB) or double sideband (DSB) use.

Explanation

When the B3 I-Task (the VMS control program) loads it queries the B3 microcomputer for the initial values of all the receiver variables. Although time consuming, this ensures that the I-Task does not attempt to retune the receiver until the operator explicitly gives the command. As B3 loads for the first time it will read a pair of initialization files, RxB.INI and RxB_LUT.INI, which will display informational messages on the TSS's screen. The second of these files defines the lookup tables and should display a message indicating when the tables were last updated (assuming the updater changed the comment line).

The B3 noticeboard is not always destroyed when B3 exits; if an older copy exists when B3 is reloaded it will be used and an informational message will be issued to that effect. If it is necessary to start with a new noticeboard (e.g. if the old one has been corrupted) it will be necessary to kill every task which connects to the B3 noticeboard. The easiest way to ensure this is probably to kill the control system and reload it.

Monitoring B3

It is worth knowing that the status screen can be run independently of whether or not B3's VAX control software is running; the status screen resides only in the B3 micro. Thus one can have the B3 status screen running at any time B3 is switched on, whether or not B3 is in use. Rebooting the B3 micro in the cabin resets the status screen immediately; if this does not happen one should reset the terminal server (power it down/up) and reboot B3's micro (a hard reboot may be necessary). Finally it is not necessary to have the B3 screen running in order to use B3; B3 will work just fine "flying blind", but the security blanket provided by the status screen will be missing.

To start up the status screen, start up a DECterm, log in, and type:

set term/device=vt100/perm lta150
set host/dte lta150

This should give you access to B3's status screens. Usually the screen will at first be garbled, but on issuing the first tuning instructions for B3, will refresh itself. If not, do not panic and also, do not rush away to reset the terminal server, since this is likely to result in more problems; instead wait an additional 5 minutes or so, and the screen will likely return to normal. If not, first try removing and restarting the screen via a new DECterm window. To refresh the display type Q. Having set the terminal to vt100 mode, the PF keys should be working; that is PF1 through PF4, which select various diagnostic and informational displays for B3.

We also recommend switching on the debug mode, assessible amongst the commands at the bottom of the B3 screen. This provides a quick visual clue as to the tuning status of B3 in the lower left corner of the screen.

Do try not to type ICL commands or other text into the B3 status screen; it may well send B3 into a very odd state, from which a reboot may be the only escape. For this reason at least, running the status screen on the separate terminal is advisable

B3 commands

The FRONTEND (fe]) command is the only one which is necessary to use RxB3 successfully in most cases. In practice there are situations where the tuning sometimes fails to run to a successful completion. Sometimes it fails to set the mixer currents to the demanded values, sometimes it may fail to recognise that the waveplate has reached the right position. Sometimes one has asked for something which B3 cannot do, or which constitutes a known fault. A couple of common fixes for "normal failures" are listed below.

ICL> rxb_auto
attempts to restart automatic tuning of the entire receiver without changing any of the settings. This is effective almost every time and should be the first corrective action taken to recover an unsuccessful tuning, or to adjust the mixer currents if they are not at the demanded values.

ICL> rxb_retune
recalculates all the lookup table positions for the tunable components in the receiver and restarts the automatic tuning. It is equivalent to tuning to a completely new frequency but without actually changing the frequency.

ICL> rxb_reboot
attempts a warm reboot of the RxB3 microcomputer, kills the RxB I-Task and reloads it. The FRONTEND action must be run again after rxb_reboot has completed. This is a real desperation measure. In almost all cases rxb_auto or rxb_retune will be more effective for error recovery. Use with extreme caution. Personally I recommend a hard ("big") reboot under such circumstances.

Other Commands

ICL> rxb_query variable_name
will read the value of variable_name back from the micro and print it on the terminal. See the b3cmnds.x file for a list of the variable names and their possible values.

ICL> rxb_fetch variable_name (ICL_variable)
will read the value of variable_name back from the micro and store it in ICL_variable.

ICL> rxb_value variable_name (ICL_variable)
will read the value of variable_name from the I-Task (NOT the micro) and store it in ICL_variable. Most of the time the micro and the I-Task hold the same values for each variable so rxb_fetch and rxb_value are equivalent. rxb_value is faster than rxb_fetch and does not require communication over the IEEE-488 bus. It is also useful for diagnosing the rare cases when the I-Task and the micro disagree over the value of a variable.

ICL> rxb_send variable_name value
stores value into variable_name in the I-Task, then sends it to the micro.