Intro

    Jade morton (now at colorado state) brought a novatel multi frequency gps receiver to ao. It was to be installed at the antenna test shack (next to the lidar lab). The system consists of a computer with a coaxial cable going out to an active antenna. A separate power supply is needed to power the antenna. The cpu will be placed in the antenna test shack while the active antenna will be on the roof of the shack.

    The picture  shows the cpu and the attached antenna (.jpeg)

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22jan14: Measuring the rfi in the screen room.

    Luis quintero measured the rfi from the antenna and receiver on 22jan14 in the screen room.

The setup was:

• anritsu spectrum analzyer placed inside the shielded box.
  
• An rf cable out to the 904 antenna probe
• a fiber cable going out of the screen room for control of the spectrum analyzer.
• The c program anacom was used to acquire the data
• source: /share/megs/phil/x101/anritsu/anacom.c
• command file: /share/megs/phil/x101/anritsu/cmd.dat.100_3000mhz
• The command file configured the spectrum analyzer to:
• 512 points
• 30khz rbw
• preamp was on.
  
• step from 100 to 3000 Mhz in 100 mhz steps
• take 10 sweeps at each step.
• store avg and peak hold at each step
• The 904 E field probe was used (more info)
  

The plots show the results of the measurements:

• the black lines show the 10 sweep average
• the red lines show the 10 sweep peak hold.
  
• 904 probe at the antenna (.pdf)
• 904 probe at the front of the cpu (.pdf)
• 904 probe at the back of the cpu (.pdf)
• 904 probe with antenna, cpu off (.pdf)
• This measures how good the screen room is (with the anritsu in it's shielded box).
  

Summary:

• The largest spikes that are inside a receiver band are
• near 425 Mhz
• above 1500 Mhz . Looks like there is a spike at 1500 Mhz
• We should test this on the telescope with some on,off's of the device looking at 425 and 1500.
  

processing: ~luisq/rfi_test/20140122_*/

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