3.8.3 Physical Layout of the Racks - SIS345

Most of the controls for the SIS345 are located in the three racks beside the left flange.

In the left-most rack beside the receivers, you will find:

• Host 1 - a computer used to control the HP synthesizers in the past.

• The HP Synthesizer for IF-A.

  This is the one usually used by the SIS230/SIS345 receivers and so is labeled 230/345. Usually this is under remote control. The number on the synthesizer should match the number sent by FEORGA.

• The HP Synthesizer for IF-B.

  This is the synthesizer used for the SIS490 receiver, and so is labeled 490. Usually this is under remote control. The number on the synthesizer should match the number sent by FEORGA.

The second rack is mainly for use with the 345 GHz receiver. Many of the controls are required for controlling the LO chain and will be adjusted by the staff before you use the receiver.

Do not randomly flip switches and turn dials - you could kill your mixer!

• Mirror Assembly Motor - At the bottom of the center rack there is the mirror assembly motor control. By selecting up/down and fine/coarse, you are able to control the direction and speed of the SIS mirror assembly. See section 3.4 for the gory details.

• Line Injector Motor - at the bottom of the center rack, you will find the Line Injector system, used for checking the line frequency. See section 3.6 for details.

• Tertiary Mirror Control - at the bottom of the center rack, to the right of the Line Injector Motor, you will find the RIGHT and LEFT buttons for the Tertiary mirror. It should be set to LEFT for the SIS345.

• Mixer V/I Display - At the top of the center rack is a display:
  • Mixer voltage (left-most monitor).
  • Mixer current (center monitor).
  • Difference in SIS345 mixer current (channel 1 - channel 2).
  The mixer displayed is selected by the observer using the mixer monitor dial in the right-most rack.

• Mixer 1 Bias Controls - This area of the rack contains the controls for the mixer bias voltage as well as a sweep feature. The sweep is the UPPER dial, the bias voltage is the LOWER dial. The sweep is there to allow you to get a sense of the voltage curve. However, you do not have to use the sweep - just adjust the mixer bias up and down and watch what it does.

  Never turn off the mixer bias.

  The observer needs to be careful to make sure that he turns off the sweep after use (otherwise you will have a very unstable receiver!). Also, the dials and on/off switches are very tightly packed - so be careful of which switch you touch!

• Mixer 2 Bias Control - Located directly below the mixer 1 bias controls, this area of the rack contains the mixer bias and sweep controls. As with the Mixer 1 bias controls, be careful of what controls you touch - and turn off the sweep.

  Never turn off the mixer bias.

• Magnetic Field Controls - These are located above the mixer bias controls. Depending on the setting, the observer controls either the magnetic field for channel 1 or channel 2. A common mistake in tuning is to adjust channel 1 when meaning to adjust channel 2 (or vice verus). Look at the dial or switch you are tweaking - make sure it is the right one.

• Total Power Meter - In the center of the center rack you will find the total power meters for IF-A (usually the SIS230 receiver or channel 1 of the SIS345 receiver) and for IF-B (usually channel 2 of the SIS345 receiver or the SIS490 receiver). It allows the observer to maximize the power level while tuning.

The rightmost rack is used extensively in tuning all the SIS receivers.

• Phase Lock Monitor - At the top of the right rack is the phase lock monitor display. You will watch this display to see the pip of the phase lock when tuning.

• AOS/Mixer Display Panel - This white box controls:

  1.

  Which AOS to Display - left top dial.

  AOSA, AOSB, or AOSC (Filterbanks are not displayed)

  2.

  Which Mixer to Display - right top dial.

  test=1, SIS230=2, SIS345=3, SIS490=4, HEB=6

  3.

  AOS or Mixer to be Displayed on Oscilloscope - top switch.

  4.

  Channel A or Channel B (of the SIS345 receiver) - middle switch

  5.

  I-V or TP-V Display (on Oscilloscope) - bottom switch.

  6.

  Reset Button for AOS currently selected - big red button. Only resets the AOS selected by the AOS dial. Don't forget to check others!

  The setup button on the Oscilloscope controls whether you are looking at the output of the (chosen) AOS or the mixer (either I-V or TP-V).

  • To select AOS, press the setup button until the number 1 appears.

    press reset at bottom of oscilloscope.

  • To select the appropiate mixer, press the setup button until the number 2 (SIS230), 3 (SIS345), or 4 (SIS490) appears.

    press reset at bottom of oscilloscope.

• The SIS345 Receiver control program

  This box runs the SIS345 control program. It will receive the computer commands from FEORGA downstairs (i.e. from the observer) and set up the various receiver parameters so that the Gunn will lock at the correct frequency. In general, the tuning is so automatic that the observer simply has to wait till the computer reports that the new frequency has been set (and the phase lock pip shows up on the phase lock monitor above).

  If one selects the IF section, one sees that one can control the amount of attenuation put into the two IFs. This feature can be used for controlling the attenuation of all the receivers. For example, for the SIS345 channel 1, which uses IF-A most of the time, you can increase or decrease the attenuation through this box for all the backends using IF-A simultaneously. Likewise, the attenuation for SIS345 channel 2 can be used adjusted by setting the IF-B attenuation.