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Intro

   On 22apr21  we measured the rfi at the 12meter with a discone antenna. The setup was:

• diamond antenna model D3000N discone antenna
• 25 MHz to 3000 MHz
• 2db  gain.
• The antennas positioned on a 10' pole on the north edge of the 12meter cement slab.
  
• There would be some shadowing by the 12meter in the SSE direction
• The  keysight fieldfox signal analyzer model 9916A was used to measure the spectrum and cable loss.
• The field fox was connected to the antenna by a long (>50') rg9 cable.
• The analyzer was set to:
• 1001 points
• average 10 sweeps
• power detector
• record avg and peak hold
• Different spans, resolution bandwidths (rbw) , and preamp settings  were taken. The attenuator was set to 0.
• After the measurements, the long rg9 cable was connected to the fieldfox in network analyzer mode to measure s12 (the cable loss)
• We didn't do a calibration prior to this (forgot to bring the cals:).

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Processing the data:

• The Cable loss was read in and used to correct the measured data.
• the values were converted to linear and then interpolated to each measurements span.
• The measured spectrum was increased by the cable loss to get values relative to the antenna.
• The antenna gain was 2db. The reported values were not corrected for this  gain
• For each spectrum, the total power was computed by summing the channels.
• For the 1001 channel, 5MHz rbw, a correction was made since 5*1001 is 5GHz rather than the 1GHz being measured.
• Since the antenna was 25 to 3000 MHz. Only the measured data >  30MHz was used.
• The noise floor was normally set by the spectrum analyzer (not the input signal)
  

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Plots of the rfi

    The plots show the measured rfi (.ps)  (.pdf)

• For the  spectral plots, Black is the 10 sweep average, red is the peakHold value.
  
• Page 1: cable loss
• The measured S21 value. All following plots were corrected for this  loss.
• Page 2: 30 to  1000MHz
• Top: 1MHz RBW, Preamp off
  
• I had to turn off the preamp because the input was going off scale (ADC overload)
  
• Bottom: 5MHz RBW, Preamp on
• I did not see the ADC overload warning, but there may have been saturation.
• When computing the total power by adding the channels, i scaled by 1GHz/5GHz.
• Page 3: 400 to 800 MHz spectrum
• PreAmp on, 300 KHz RBW
• Page 4-5: 400 to  1000  in 100MHz Step
• These all have 100 KHz RBW.

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SUMMARY:

• measurements were taken with  a 2db gain discone antenna, > 50ft cable, and a field fox signal analyzer
• The values were corrected for the cable loss.
• No correction was done for the 2db  gain of the antenna
• There is not much clean band between 400 and 800 MHz.
• The -105 dbm/100KHz  is a temperature of 22,900 deg K,
  
• This is being set by the spectrum analyzer noise floor.
• we are  many orders of magnitude from the sensitivity of a cooled receiver.
  
• total power levels.
• This is a sum over the frequency channels. No correction made for the 2db gain of the antenna.
• The  input signals were not necessarily stable between different measurements.
  
• 
  

• freqRange [MHz]	RBW	totalPwr in Band (Dbm)		PreAmp
  		avg	PkHold
  30-1000	1.0 MHz	-22.5	-19.6	Off
  30-1000	5.0 MHz	-21.8	-16.8	On
  400-800	300 KHz	-43.7	-31.9	On
  400-500	100KHz	-51.5	-42.3	On
  500-600	100KHz	-47.2	-38.1	On
  600-700	100KHz	-53.4	-43.6	On
  700-800	100KHz	-46.2	-34.7	On
  800-900	100KHz	-51.6	-42.9	On
  900-1000	100KHz	-72.7	-63.9	On

  
  

processing: x101/210422/12m_rfi.pro