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using the 12m,fs,rdbe at AO: an overview

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Setup:

    On 15oct21 data was taken with the 12meter, field system, rdbe backend, and mark6 recorder.
The setup was:

• 12meter tracking blank sky. The az, el was around -135, 30 deg so the telescope was looking back towards the control room..
• xband receiver used:
• udc set to center 8550 MHz at  1500MHz  (the center of the 1-2 Ghz IF). It is an upper side band (not flipped)
• the 1500 MHz was converted to 750MHz with a hi side lo (so the 750 band is flipped).
  
• 8550 is centered at 750MHz. This is sent to the rdbe's.
• The rdbe was set to:
• use 1 rdbe: RDBE2
  
• 4 channels each 16 MHz bw
• freq: 8660 (pola,b chan1,2) and 8616 (polA,b chan 3,4)
  
• The 2 bit samples were then sent to the mark6 recorder in vdif format.
• A tone at 8620 MHz was transmitted from the control room back to the 12 meter telescope.
• The signal was seen in the if/lo using the spectrum analyzer prior to being sent to the rdbe
• tone seen at 1570 MHz in 1-2 ghz IF (unflipped)
• tone seen at 680 MHz in the 500-1000MHz IF (this band is flipped in freq)

The observing sequence consisted of:

• t005aa . 1 60 second run
• offline:
• run sched on the t005.key file
• cp  t005.vex files to vlbis1 (online)
• online
• run vex2snap to create the .snp file
• start field system
• schedule= start running the schedule
• adjust the power levels in if/lo, a/d in rdbe and then digitizer quantization.
• let rdbe take data for 60 seconds.
  

Files used for the experiment:

• 	generated by sched			generated by vex2snap
  exp	.key	.sum	.vex	.snp	.prc
  t005	t005.key	t005.sum	t005.vex	t005aa.snp	t005aa.prc

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Taking the data

• start the field system (on vlbis1)
  
• fs
• schedule=t005aak
  
• # wait for rdbe to initialize
• # set the attenuator for the a/d (outside of field system)
• # set the quantization levels.. cd /usr2/oper/bin
  
• ddc_quantize_read_adj_set.py
  
• adjust a/d levels:
• Response:  result = !dbe_rms=0:19.755:20.156:-0.072:-0.848:127:73;
  
• quantize results:
• !dbe_ddc_quantize?0:0:5130690:10870932:10873959:5124419:1978:-1979:0
• !dbe_ddc_quantize?0:1:5130541:10872649:10878455:5118355:2140:-2139:0
• !dbe_ddc_quantize?0:2:5122530:10870628:10881125:5125717:1739:-1740:-1
• !dbe_ddc_quantize?0:3:5114243:10881191:10882330:5122236:1963:-1965:-1
  
• Then 60 secs of data was taken tracking blank sky.
  

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Looking at the data

• logged at oper@mk6 to get the data.
  
• The raw files were combined with vsb_fs. the combined file was:
  
• ~oper/data/tmp/t005_aa_no0001/t005_aa_no0001
• The combined (but  not vmuxed) files were copied to gpuserv0:/media/DATA0/phildata/vlbi/211015/  and then processed using some idl routines i've written (to input, demux, and print the headers)l
• I also ran vmux, m5spec.py to verify that i got the same results at the idl routines.
• vmux  t005_aa_no0001/t005_aa_no0001 5032 1600 0,1,2,3 t005_aa_no0001.vmux
• arguments:
• samples/frame= 5000bytes*(8bits/2bits) = 20000
• sec/frame=1/32MHz * 20000 =.000625seconds
• frames/sec=1/.000625=1600 frames/sec/chan
• m5spec.py t005_aa_no0001.vmux VDIF_20000_256_4_2 1000 16384
• arguments
• 20000 bytes data/frame. since we put 4 5000 byte frames in 1 frame
• 256Megasmp/sec: 32MhzSampling*2bits*4chan=128.
• 1000: integrate for 1000 millisecs
• 16384 to a 16K xform -> 976.6 hz channel resolution.

Print the headers from the combined (but not vmuxed file)

• 20 headers from t005_aa (.txt)

There is no longer a problem with the headers.

• The previous problem (11oct21) was probably because we requested 2 channels, but a single rdbe always outputs 4 chan.

The voltage distribution and the spectra.

    In idl

• 4096 frames of voltage data were input and demultiplexed into the 4 channels (2 pols)*(2 freq bands)
  
• This was done twice for each experiment:
• using output thresholds of : [-3.3349,-1,+1,3.3340]  to compute the spectra
• using output thresholds of : [0,1,2,3]    when making the histograms

The plots show the spectra and voltage histograms for the 2 experiments:

• t005   spectra/histograms (.ps) (.pdf)
• This used netside=u,u in the .key file
• page 1: spectra
  
• The top plot is polA,B for the 8600 band
• The bottom plot is polA,B for the 8616 MHz band
  
• the setup parameters are listed
• The  tone (at 8620 MHz) is showing up at + 4MHz in the 8616 MHz band
• So it looks like the specified freq is the edge of the band.
  
• Page 2: voltage histograms:
• The 4096 frames (using lut values [0,1,2,3] for min to max values were used to make a histogram
• Black is polA, red is polB, blue is the histogram from the rdbe_quantize command query.
• the histograms have been normalized to the average counts in channels 1,2
  
• Top: 8600 MHz band
• bottom: 8616 MHz band
• The ratio of the levels is about .46 ..
  
• it is the same for the quantize histogram as well as the recorded data.
  
• The recorded voltage rms was computed:  1sigma was about .945  digitizer levels. The optimum value (for clipped data) should be .94  so the rms levels are correct.
  

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Summary

•  the rdbe is always outputting 4 bands.
• We saw the 8620 MHz tone 4 MHz from the  edge of the 8616 MHz band
• so the recorded freq values are the edge of the band.
• The quantize routine that is being used to set the quantize levels is doing it correctly.
  
• The test was done in evn mode using recorder= flexbuf:mk6  (in the vex2snap command).
  

processing:x101/211015/fstest.pro