Background:

What we did:

• The mesh was in the 8Mhz position (15 feet below the 5 MHz position).
• the reflected power cables were connected to the tx side of the load/ant switch.
  
• This brought the dipole signal back to the hf ctrl room.
• 
  
• data acquisition equipment:
  
• the anritsu spectrum analyzer was run continuously with:
• 2 Mhz span, 10KHz rbw, cfr 8.175 Mhz, 25 sweep averages.
• data was taken with the preamp off and later with preamp on.
• 8Mhz dipole 1 was plugged into the anritsu
• this is a radial, positioned 60 degrees east of north.
  
• 2 sdr's were used to record i/q data (more info)
  
• sdr 1: a lowbandwidth of 240KHz then later 480KHz bw. cfr of 8.175Mhz then 8.249 Mhz
  
• sdr 1:a wider bandwidth of 2mhz was used. cfr=8.175Mhz
• What a detection would look like.
• The sun transits around 12:33pm
• For these days, it was passing within .5 deg of overhead.
  
• the Beamwidth of the 8Mhz system should be about;
• using hpbw=K*lambda/diameter gives
• hpbw=1.2 * 36.7/300 = .147 Radians= 8.4 deg.
  
• It is probably less than that because of the blockage of the mesh..
  
• So lets use 10deg for  the beamwidth
  
• the earth moves at 4 minutes/degree
• So the sun will move through the beam in about 40 minutes (to the half power points)
• we used only 1 dipole rather than all 3 pairs.
•  Felix modeled this and said the beamwidth stayed about the same, but the sidelobes went up.
• The bandwidth of the balun/dipole is supposed to be about 100KHz.
• So taking 100KHz total power about 8.175 Mhz, we should see:
• the signal will start to rise around 12:15
• peak at 12:33
• and go back down to the initial level around 12:50.
  
• Data acquired:
• 180727 18:30 to 180730 08:30
• anritsu run continuously, the preamp was off.
  
• telescope was in use during this time by regular observers.
• 180731 to 180803 around lunch time. the anritsu preamp was on.
  
• for transit, the azimuth was at 270 deg. It wasn't till the last day that i realized we needed to disable the drives with the emergency stop button.
  
• 180731 09:55 to 13:00.
  
• 180801 11:20 to 13:20
• 180802 11:20 to 13:15
• 180803 11:05 to 13:00. Used emergency stop to try to force vertex shelter off.
• Using the ionosonde, fof2 was  5-6 MHz  at noon during the observations.
  

Making the plots and images:

• Making the dynamic spectra
  
• they were flattened by:
• compute median bandpass for data set
• fit an 18th order harmonic function to this
• divide this into each spectra.
• this will remove the bandpass structure, but variations in the spectra will be seen.
• The green horizontal line is the sun transit (12:33)
• the red vertical line is 8.175 MHz.. the center of the balun.
  
• Making the plots
  
• Page 1: average and median spectra for the dataset
• some days have a second set (in different colors) where the rfi was lower
• Page 2: 100KHz total power about 8.175 MHz.
• This should be the center of the baluns
• colored lines are flagged where sets of spectra are overplotted in the lower panel.
• This was looking to see if the bandpass shape changed.
• Page 3: azimuth position, torques, and 100KHz total power
• top; azimuth position during data set.
• some red lines show where the azimuth state changed (or 15 minutes after a state change)
• 2nd: azimuth motor torques vs time.
• when the motors are disabled, the torques go to zero, but:
• 15 minutes after disable, a small current is run through the motors to keep them warm.
• this is what is causing the rfi even when the motors are stopped.
• 3rd: 100KHz total pwr vs time. The red flags show where the rfi goes away when the motors are disabled and then returns 15 minutes later when the heating current is applied.
• 4th: 100KHz total pwr vs azimuth.
• For 03aug18 this shows how the azimuth dependence of the  power  coupling into the dipole
  

The dynamic spectra and plots:

Measuring S11 from the hf ctrl room

    On 02aug18 S11 for the 8MHz radial dipoles was measured from the hfctrl reflected power panel (The signal output)

•  The keysight network analyzer was used.
• +/- 1 Mhz about 8.175 MHz was swept.
• No calibration was done (sorry dana...)
• The mesh was at the 8Mhz position .

• Each radial dipole is a different color
• black: dipole 1 (at az=60deg)
• red : dipole 3 (at az=180 deg)
• green: dipole 5 (at az=300 deg)
• a blue line is at 8.175 MHz. The dashed blue lines are +/- 50KHz .
• The minimum is at 8.3 MHz.
• The broadband noise from the motors was also centered around 8.8 MHz.
  

Summary:

• The 8 Mhz dipole 1 (radial at az=60deg) was used to try and detect the sun.
• The sun was within .5 deg of overhead during the observations.
• The sun was not seen in any of the data.
  
• 27-30Jul18 data was taken while the telescope was moving.
• this caused a large amount of broadband rfi.
  
• 31Jul18 - 02Jul18 - data was taken with the telescope stopped, but we still had lots of broadband rfi.
• The problem with rfi when the motors are disabled come from:
• After the motor currents are off for 15 minutes, the vertex control system send a low current through the motor windings to help with condensation.
• For this current to flow, the master contactor has to be closed (to supply the power).
• Pushing emergency stop will force the master contactor to remain open. This will prevent the warming current from turning on.
  
• 03Jul18: the vertex emergency stop button was used to prevent the motor warming current to flow.
• the broad band rfi was not present.
• at sun transit the 100KHz total power was -105 dbm with no sign of the sun.
• the azimuth dependence of the motor noise  was a maximum when the azimuth aligned with the radial dipole.
• S11 was measured for each dipole (with no calibration).
• the band was centered at 8.3 MHz rather than 8.175 MHz..
  

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