Subject: 3.1.1 Feed/LNA

The Feed/LNA component consists of log-periodic feed that sends incoming RF signals to the tip-circuit board and then via a pair of transmission lines to the Low-Noise Amplifiers (LNAs) in the cryostat. This unit is mounted at the secondary focus of the antenna with a bracket attached to the primary. The mount has one degree of "in-out" motion to adjust the focus for optimum performance as a function of observing frequency.

Monitor Points

- atagetitem cryotemp, cryopower and cryorejtemp.

Maintenance Procedures

- Jump start ion pump with Varion vacion. Use this when ion pump driver is over currented. Drive pump with Varion 15s on, 15s off. Approximate time required .5 hr.

Field Repairs

- Feed Swap , .75 hr. Replace Pax Box , 1 hr.

Test Procedures

When the Rimbox, Paxbox or Feed are replaced use this procedure on ant00. Required time approximately .75 hr. Static Test:

1. Hook rimbox to static breakout jig and power up.
2. Measure DC voltages on all test points. Use pos probe on left strip and gnd probe on right strip.
3. Do not continue unless all voltages and polarities are correct.

Dynamic Test:

1. Power down rimbox and remove static breakout jig.
2. Connect rimbox to paxbox case. Connect the the 2 black optical fibers from the control box to the rimbox controller card. Inputs on the card are labeled alidade-rim.
3. Open two terminal windows. From one SSH into ataant@antcntl. From the other SSH into obs@user1.
4. Power up ant00. You should hear the cryo pump humming.
5. From either window do atastatus and wait for ant00 to show up on the status window.
6. From user1 do atagetitem cryotemp then cryopower then cryorejtemp. The cryotemp should start around 290 k and gradually ramp down to 60 k. Cryopower can be as high as 100W and will ramp down as the temp comes down. Cryorejtemp should not exceed 50C and will likely be around 30C. If any of these are out of range shut down the cryo by pulling the bottom plug on the cryo card.
7. From Antcntl ssh into ant00. Netcat rimbox 23. Type getonboardtemp, the return should be approx. 30C. Type getsoftwareversion, this changes as it is updated so make sure it is the current version. Type cntl-c to exit netcat.
8. Type netcat pax 23. Type lnabiaslatch , should return OK. Type getid x return should be ~30 but not > 100. Type getid y, same as x. Type lnabiasoff.
9. From user1 type atagetitem ant00 adc08. This is the voltage output of the paxcase thermistor. Type tec.csh and the voltage. The return is the paxcase temp. It should regulate at 20C. Do the same for adc09 and adc10. These are pax air and pax heat sink respectively. Use tec2.csh for these.
10. Turn off ant00 and label the rimbox good.

Gary Gimblin