History:

• 24jun11 : llb500-00600 distomat installed next to distomat 6 (az=330). It is currently turned off.
• 20jun11: ?? about this time llb-60 removed from distomat 6 position (so luis could use the rfi canister for his tests).
  
• 15jun11  : luis tests llb500-00600 distomat in screen room.
  
• xxjun11   : tried to purchase llb-60-d distomats, but they no longer make them. They send us the newer model llb500-00600.
  
• midapr11: llb-60-d distomat installed at rim road next to distomat 6 (az=330 deg). left running
  
• 06apr11: llb-60-d distomat tested in screen room by luis.
• ??????? : llb-60-d distomat  installed on platform, looking down at retroreflector on ground.
  

15,23jun11: (LLB500-00600) rfi measured in screen room

• TRelectronics (LLB500-00600) distomat.
• agilent E4445A spectrum analyzer, 601 channels, and preamp on.
• DC to 3200Mhz in 250 Mhz junks (416Khz/chan).
  
• ETS model 7405 near field probes (.pdf):
• 902 probe: magnetic field. resonant freq 1.5 Ghz
• 904 probe: E-field upper resonant freq > 1Ghz
  
• Move the probe around the device looking for maximum value (spectrum analzyer set to max hold).
• Data was taken with the distomat sitting on the bench open (15jun11) and then repeated (23jun11) with the distomat in the shielded canister (but the window as not covered).
  

• There is a comb with 320 Mhz spacing. The dotted vertical line flags every 320 Mhz.
• Page 1: no shielding Efld probe
• Page 2: no shielding Bfld probe
• Page 3: shielding Efld probe
• Page 4: shielding Bfld probe.
• Also see luis's report on the unshielded test (.pdf)

Summary:

• The 320 Mhz comb is seen up to 3200 Mhz (as far as we looked)
• The strongest birdie is at 2240 (320*7)
• no shielding: -32dbm (about 50db above noise floor)
• shielded: -50dbm (30 db above noise floor).
• so shielding is knocking it down by about 20db.
• Luis mentioned that with the shielding, the strongest rfi is coming from the window where the laser exits.
• This opening was completely open (there was no wire mesh on the opening).
• For telescope testing
• we can probably see the 2240 birdie (it's not too contaminated by other rfi).
  
• The 1600 birdie might also be visible (if glonass is not up).
  

06apr11: (LLB-60-D) rfi measured in screen room. (top)

• TRelectronics (LLB-60-D) distomat..
• agilent E4445A spectrum analyzer, 601 channels, and preamp on.
• 300 MHz  to 10 Ghz. I've included the data from 300 MHz to 7500 MHz.
  
• ETS model 7405 near field probes (.pdf):
• 902 probe: magnetic field. resonant freq 1.5 Ghz
• 904 probe: E-field upper resonant freq > 1Ghz
  
• Move the probe around the device looking for maximum value (spectrum analzyer set to max hold).
• Data was taken with the distomat sitting on the bench and then with the distomat in the rfi shielded canister that is  normally used when used on the telescope. Note that they the exit hole for the laser beam does not have the shielded window that we normally use.

• below 1100 Ghz, frequencies were tested that corresponded to the 327,430, and 800 receivers.
• above 1100 Ghz the coverage was continuous (we need to check the response of these probes to the high frequencies).
• page 1-2 EFld probe no rfi canister
• page 3-4 HFld probe no rfi canister
• Strong birdies were found at :
  
• A 320 MHz comb was found (maybe 160 MHz?).
• Other birdies were found at 1200,1437+/- 62.5, 1677.8,3249.7 MHz
  

• page 5-6 EFld probe with rfi canister
• page 7-8 HFld probe with rfi canister
• the 19th harmonic of 320 MHz (6080 MHz ) was strong even with the distomat in the cannister.

Summary:

• distomat has 320MHz comb.
  
• other birdies at 1200,1437+/- 62.5, 1677.8,3249.7 MHz
• the 19th harmonic of 320MHz (6080) is strong even in the rfi canister enclosure.
• need to check to see if shielding the exit pupil helps.