Intro

    The filter bank box for the 12meter will reside close the to the dewar in the 12meter hub. It contains various digital elements that cause rfi:

•  rasberrypi,  fiber to ethernet converter,  ethernet to sub converter..etc

    We placed the huffma box in the screen room and ran some rfi tests to see how well the shielding worked.

• 02mar23 - we tested the system with a 1 gbit ethernet to fiber transceiver.
• 06mar23 - we re tested the system with a 100 Mbit ethernet to fiber transceiver.

---

Setup:

    The setup was:

• box placed in the screen room
• 1-10ghz log periodic antenna used
  
• 100Mhz to 10Ghz 25 db amp attached close to antenna
• cable from screen room to fieldfox (outside screen room)
• field fox spectrum analyzer used for measurements
• 300 Mhz span, 30khz rbw,10001 points, rf attn=0, avg detector
• avgerage 10 sweeps. record avg,maxhold,minhold  (about 70 second to avg 10 sweeps)
• Step cfr from 2400 to 9900 Mhz (26 steps)
• Do a complete set of measurements with box open (antenna close to openning(
• do a complete set of measurements with box closed and antenna close to output cables on side of box.
• this had the strongest leakage.
• Datataking: x101/rfiscrn/ffscrn  cmd_ffwbfb.dat  
  
• output files: /share/phildat/wbrcvr/scrn/filterbank/fb_(opena/closeda)_yymmdd_nnnnn.dat
• Each file as a 10 sweep average for a 300 Mhz span.

---

Looking at the data

    The data for each measurement (lid open, lid closed) was first read in.
The  26 spectra of  10001 points,  300MHz span were concatenated into 1 large spectra.
The 10 sweep average was used for the plots.
   
    Plots were made from

• The 02mar23 data (1 gbit transceiver)
• The 06mar23 data (100 Mbit transceiver)
  

The first plots show the average spectra across the band:

• Top frame :lid open

• Vertical scale dbm input at field fox (after 26 db external amp).
• black:spectra
• red:  spectra smoothed with a 1001 length median filter (30MHz).
  
• this is used for the the noise floor of the measurement.
• bottom frame:lid closed.
• the step in the spectra at 7.5 GHz is probably the band step of the field fox.
• the noise floor is being set by the field fox noise floor.
• 02mar23 with 1 gbit transceiver (.ps) (.pdf)
• Box open has spikes above -65dbm (in 30Khz rbw)
• box closed has spikes up to -83dbm
  
• 06mar23 with 100 Mbit transceiver (.ps) (.pdf)
• box open max spikes -84dbm (in 30khz rbw)
• box closed: no spikes seen above the noise floor (about -97dbm)

The 2nd plots show the spectra divided by the noise floor:

• Page 1: spectra divided by the noise floor
• top: box open
• bottom: box closed
• the red + are points 6db above the noise floor when the box is open.
• Page 2: 230302 box closed blowups in freq
• Page 3: 230392 : blowup strongest peaks around 3 Ghz.
• 02mar23 with 1Gbit transceiver (.ps) (.pdf)
• page 1:
  
• box open. peaks up to 35 db above the noise floor
• box closed: peaks up to 17 db above the noise floor.
• Page 2: blowups 2.4 to 5ghz and 2.8 to 3.4 Ghz
• Page 3: blowup showing strongest spikes around 3 GHz.
  
• 06mar23 with 100Mbit transceiver (.ps) (.pdf)
• Page 1
• box open peaks 17db above the noise floor
• box closed: no peaks above the noise floor.

The 3rd plot shows the box rfi reduction for 230302 (1Gbit transceiver) (.ps) (.pdf)

• Top overplot box open and box closed(red)
• bottom: boxopen/boxclosed
• some peaks were reduced by up to 29db 
• the 06mar23 data (with the 100 Mhz transceiver) was not plotted since there were no spikes above the noise floor with the box closed.

---

SUMMARY:

• There are many points 10db above the field fox noise floor when the lid is closed.
• We need to see how these are getting out and then improve the shielding.

Resolution:

•  First set of probing showed that the stronger rfi is (2.500070Ghz) is coming out of the holes in the side of the box from the ethernet switch.
• Turning the switch off made them go away.
  

processing: x101/230111/dwmon_rfi.pro

---