….INSTRUCTIONS FOR USING BARNEY with SMA PLL….

Feb 12, 2009. RAChamberlin

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

When asked, answer NO to moving the sidecab mirrors.

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

Note: LO/IF=4.5 sets the Gunn LO so that Doppler tracking always centers the source's expected VLSR at 4.5GHz in the IF. The FFTS is a 0.5 or 1GHz wide spectrometer that can be moved around in the IF band. FFTS=4.5 centers the FFTS band on 4.5 GHz. For more details see http://puuoo.submm.caltech.edu/docs/hiro/ffts/FFTS_Instruction.html.

3. UIP> TERT CASS

4. Make sure M3 in relay optics is rotated to correct position

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.

If it is not, jiggle cables on from SIS bias box to top of dewar until you get some indication of quiescent current. If jiggling doesn't work don't worry too much. The current information is not used in the SIS bias feedback. The LO has now been configured so that you cannot put enough power in the VDI multiplier to destroy it.

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. Remove the 50 ohm termination from the BNC cable on the deck labeled "HM IF" and connect it to the spectrum analyzer input. Set the spectrum analyzer center frequency 109 MHz and and the span to about 20 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.

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. Another indication that you can use is the output of the "LO Management Box". When the indication is about 0.17 volts you are hitting the VDI multiplier with enough power.

Note; As of Jan 23 the LO Management box is fixed. 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.

9. Load the appropriate pointing file: UIP> POINT BARNEY_CASS 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 850GHz PLL monitor cable to spectrum analyzer. Terminate cable from side cab pll with 50 Ohm load. For 850GHz 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