….INSTRUCTIONS FOR USING BARNEY with SIDECAB PLL….

JANUARY 20, 2009, RAChamberlin

Updated: Jun 19, 2009

1. UIP> LO 12CO3-2-4 3 /LOCK=NEW/IF=4.5 /FORCE

When asked, answer NO to moving the sidecab mirrors. Note that sidecab receiver channel 3 is being used for the LO system.

MOVE SIDECAB MIRRORS? > NO

2. UIP> SPEC/AOS5/FFTS=4.5/RESTART

3. UIP> TERT CASS

3.3 UIP> POINT BARNEY_CASS

4. Make sure M3 in relay optics is rotated to correct position. Rotate by grabbing base rather than the mirror flat.

4.5 Remove plexiglass covers from M3 and M5 in relay optics.

5. On Barney SIS bias box make sure voltage is zero'ed. Move toggle switch from "DUMMY" to "RX". Bias to 2.2. mV. Quiescent current should be about 0.024 mA.

5.5 On the Barney magnet bias box make sure the current is zero'ed and then move the toggle switch from "DUMMY LOAD" to "MAGENT". The bias box has two channels: use the top channel. The lower channel is not connected. Set the magnet bias to 30 mA.

6. Connect the cable coming from the sidecab PLL to the spectrum analyzer on the alidade. (Remove the 50 ohm termination from the cable and connect it to the disconnected cable from the SMA PLL.) Set the spectrum analyzer center frequency 20 MHz and and the span to about 5 MHz

7. Lock the Gunn in the normal way. The Barney Gunn is H473. A data sheet is taped

to the right side elevation bearing. On Jun 19, 2009 the sidecab PLL loop gain had to be adusted to 1.72 (on the potentiometer) to get a lock.

8. Un-attenuate the LO by turning the knob in the CW direction. Set the SIS bias current to 0.085mA. While doing this watch that you see a change in the in the total power on the warm IF amplifier module mounted in front of the receiver. If you see power going up, but no change in current, the connection at top of the dewar may be flakey. Try jiggling the cables from the SIS bias box to the top of the dewar until you see the current go up and settle down. Continue setting the LO attenuation until you get 0.085 mA.

LO Managment Box: The maximum voltage you should allow as you reduce attenuation is 0.46 Volts. In addition, a fixed attenuator (about 3 dB) has been put on the LO chain to prevent more that 30 mW of Gunn power from the hitting the multiplier. With this fixed attenuator in the LO chain there should now be no danger of burning the multiplier. ) As of May 2009 the SIS Bias current indication is not working reliably. It was found that an indication of about 0.26 volts on the LO Management Box gives about the right response from the IF. On Jun 19, 2009 the SIS current indication is working again. This intermittent problem might be due something wrong with the dewar connector.

9. Usually Barney is used on the Left Hand Side (LHS) of the cass focus relay optics. For the Jan 20, 2009 run the LHS is occupied by the 850GHz rx. Therefore the appropriate pointing file is probably for Frank's rx (Z_RX) which normally sits on the Right Hand Side. I.e., UIP> POINT Z_RX and try to point up on an object.

…Shutting down Barney…

1. Fully attenuate LO but turning the knob CCW screw it out. Watch that current and IF power go down (not up).

2. Set the SIS voltage to zero. Move the toggle switch to "DUMMY".

3. Set the Magent current to zero. Move the toggle switch to "DUMMY LOAD".

3.5 Replace plexiglass covers on mirrors.

3.7 Reconnect SMA PLL monitor cable to spectrum analyzer. Terminate cable from side cab pll with 50 Ohm load. For SMA GHz rx set spectrum analyzer center frequency to 109MHz and span to 20 MHz.

4. To restore side cab rx operation:

a) UIP> LO 12CO2-1-3 /LOCK=NEW/IF=1.5/FORCE

b) UIP> TERT SIDE

c) UIP> SPEC/ AOS5/FFTS/ RESTART