28feb11 - azswings while transmitting tone from 12m (top)

    On 28feb11 we did 4 azimuth swings using the 327 receiver while transmitting a tone from outside of the 12meter telescope.
 The setup was:

• 327.7 Mhz tone transmitted from outside the 12meter pedestal (not sure if it was locked or not).
• mock spectrometer:
  
• 8192 channels,57Mhz bw, 1 sec sampling:
• telescope:
• azswings za=15, 270 ->630 and back at .35 deg/sec
• azswings za=12, 270 ->640 and back at .35 deg/sec

• extract the channel with the birdie
• compute a bandpass using the median value +/- 75 chan from the tone
• divide the bandpass into the tone power (to make the units Tsys)

• Black is the Clockwise swings, red is the ccw swings
• Top 2 frames: za=15 deg
• The red ccw swing has peaks at:
• az=38.87,k az=44.60
  
• the 38.87 az is also the peak for the CW swing
• Bottom 2 frames. za=12deg
• The peaks are at:
• az=-7.18, 38.40, 56.78

Summary:

• It looks like 38.87 would  be a good az to use when za=15 for monitoring rfi from the 12 meter.

25feb11 - Checking rfi inside pedestal (top)

• rhode & schwartz spectrum analyzer
• 6 cm loop antenna for close in measurement of Ethernet transciever
• yagi ant for other measurements.
• the dehumidifier was turned off (but the spectrum analyzer was on).

• 001: Ethernet converter in Cabinet
• all 24 volt fuses in cabinet were off except f10 (Ethernet)
• main contactor open.
• loop antenna laced next to Ethernet transceiver.
• 0 to 1 ghz span,  peak hold
• This showed the comb from the Ethernet transceiver.
• 002: Yagi pointed at open Cab.
  
• span 0 to 1 Ghz
• Pedestal door closed, cabinet door closed.
• moved az, el during peak hold
• Horizontal pol
  
• 003: same as 002 but vertical pol
• 004: Yagi pointing at Pedestal door
• span 0 to 1 Ghz
• pedestal door closed, cabinet door closed.
• main power switch to cabinet off.
  
• This looks at rfi leaking into the pedestal from outside
  
• 005: same as 004 but yagi now pointing at cabinet
  
• 006: Yagi points at Cab.
• span 0 to 1 Ghz
• horizontal pol.
  
• pedestal door closed, cabinet door closed.
• move telescope during peak hold
  
• 007: same as 006 but  Vertical pol
• Tests 8-12
• Were done at 327 MHz with a 100 MHz span
• They go through the power off to operate state transitions.
  
• 008:  Yagi points at Cab door 327 MHz
• Pedestal door closed, cabinet door closed
• Main power breaker off.
  
• 009: Same as 008 but turn on main breaker
• 010: Same as 009 except turn to standby mode.
• Standby mode closes the main contactor but the motors are not energized.
• 011: Same as 010 but turn switch to operate mode.
• Operate mode energizes the drives and releases the brakes.
  
• 012: Same as 011 but move telescope with hand controller
• Glitches appeared in the peak hold spectrum whenever the  switch on the handcontroller was pushed.
• Looks like rfi coming from contact closure of hand controller.
• Data set at: /share/megs/phil/x101/110225/xxx.DAT

• Page 1: 0 to 1Ghz span tests 1 through 7.
• Top: Tests4,5. System power off.
  
• Black has yagi pointing at pedestal door, green has yagi pointing at cabinet door (both were closed).
• The vertical stripes show the locations of the Ethernet transceiver comb (frame 2).
• The large signals are the FM band, and TV stations. These are leaking into the pedestal from outside.
• The pedestal door is not rfi tight. It does not make metal on metal contact all the way around.
• 2nd: Test 1: Ethernet Transceiver comb using loop antenna.
• The loop antenna was placed next to one then the other transciever.
• The was: 62.6418*N Mhz.
  
• The odd harmonics are stronger than the even harmonics. it is seen up to 939 Mhz (we only looked at up to 1GHz).
  
• The rfi is strong since the loop antenna was right next to the device.
• 3rd: test 2,3. cabinet door open, yagi antenna, move telescope.
• black is horPo, red is verPol
  
• The vertical dashed lines show the location of the Ethernet comb.
• looks like lots of rfi around 200 MHz with a spike close to 300 MHz
• This gives an idea of where the strongest rfi is located.
• bottom: test 6,7. Cabinet door closed, move telescope
• the colored traces are:
• Black is horPol
• Red if VerPol.
  
• Green is test 4 with system power off to show what was coming in from outside the pedestal.
• There is nothing that stands out from the green trace when the system power was off except for a few glitches. These probably came from the hand controller when the contact was closed.
• Page 2: 327 MHz, 100MHz bandwidth, sequence through power off to system running
• the yagi was used with the cabinet door closed.
• the 4 traces are:
• black: main breaker off
• red: main breaker on.
• green: standby mode: main contactor closed, motors not energized.
• purple: operate mode: motors energized, brakes off.
• The dashed blue line is part of the Ethernet transceiver comb.
• The dashed purple lines try to align some spikes in operate mode with the other 3 traces.
• It's hard to see if there is any rfi coming from the system since the power off trace had so much rfi coming from outside.
• there may be a few lines 280 to 300 MHz (vertical dashed lines) that seemed to appear in operate mode.

Summary:

• Rfi is leaking into the pedestal probably through the door (or maybe the cables).
  
• If rfi can leak in, it can also leak out. We need to fix the door.
• The Ethernet transceiver has a comb at 62.6418*N Mhz. It was not seen with the cabinet closed.
• Things to try:
• Find the az, el of main telescope that gives maximum rfi for a signal from the 12meter location.
• put a signal generator with an omni directional antenna outside the pedestal then do some az swings to find where the az,za peak is.
• After finding the az,za peak for rfi from the 12meter location:
• move dome to that location.
• take data with 327 receiver.
  
• go through the power sequencing  doors open.. look to see where the peaks are. You can use the time correlation to decide what is coming from the 12meter.
• go through the power sequencing with doors closed. Look to see if you can see anything.
  
• since you know the strongest frequencies from the doors open case, you might want to try to match spectrum channel width to the rfi width to optimize the detection.