Baseband test with 213 MHz bw:160927

  

    We tested  a setup for:

•  running puppi in baseband mode with 213 MHz bandwidth while also..
  
• running wapps  in spectral dump mode as well as the mocks.
  

setup:

• puppi:
• For HI absorption in our galaxy, we needed 1420 MHz in the puppi band
• A wide bandwidth was also wanted for scintillations
• The absorption occurs during the burst, so we needed  baseband data.
• For baseband samping we needed an anti aliasing filter for the lbw data.
  
• we found a bandpass filter 140 MHz bw, centered at 1600 MHz that we put in the first IF (1-2 Ghz) that goes to puppi.
  
• It was 30 db down 1505 and1697.
• This crosses the 200 MHz boundary (1400 -1600)... so we increased the clock from 200 to 213 MHz
• the band 1491 to 1704 will now fold down to bandband (7 folds) so the final band is flipped..(IF1 is not flipped).
  
• The center of the 213 MHz band in IF1 is 1597.5 Mhz
  
• The filter was inserted after the 1st 10db pad and before the first amp int the  puppi chassis.
  
• We needed more power  so we removed the 10db pad an put in a circulator.
  
• iflo
• The center of the 7th nyquist zone 1491-1704 is  1597.5
• We wanted to put 1420 MHz sky freq here..
• the 1st IF is centered at 1500 Mhz
  
• We mix the requested sky freq to 1500. IF1 1597.5 is 1420Mhz Sky freq, So IF1 1500 is 1322.5 sky Freq. This is the rf freq for cima
• The wapps  then selected all of lband using the 2nd lo's..
• centering 1322.5 Sky in the center of the 1Ghz 1st IF, gave an IF1 sky range of 822.5 -> 1822.5. More than covering lbw.

Taking data.

• puppi was run in command line  mode (cima did not control it).
• adjust the wapp power levels
• setup puppi for:
• bw='-213', raw mode, cfr 1420 MHz, 32 channels
• adjust puppi power using command line
  
• start things going
• you need to manually stop puppi.

Testing the setup:

• we took 1 10 sec scan while transmitting a birdie at 1423 MHz (into the lbw receiver).
• a second 10 sec scan was taken while transmitting a birdie of 1433 MHz
• These would check if the frequency was centered correctly, and that the channel spacing was correct.

Looking at the data:

• The raw files were copied from the gpu's to  megs3.
• the idl routines to read raw puppi data were used to look at the data.
•  2^20 length spectra were computed for the 2 gpu channels that had the 2 different birdies
• gpu07 chan 0 for 1423
  
• gpu06 chan 2 for 1433
• DC was removed, the spectra were computed and then plotted.

The plots show the spectra for the two tones (.ps) (.pdf):

• The bandwidth of each channel was : 213/32=6.65625 MHz
• 2^20 samples gave .157 seconds of data..  a freq resolution of 6.3 Hz.
• Page 1: 1423 Tone. gpu07
• top: Spectra for polA,B (black,red). smoothed to 812.5 hz (so plot file didn't get too big)
• The birdie on the right is the 1423 tone,  the birdie on the left is an alias (probably from the pfb filtering ?)
• middle: spectra averaging polA and polB.
  
• The small bump at 1420.4 MHz is probably galactic hydrogen.
• Bottom: hires plot of 1423 birdie. 6.3 Hz resolution. The birdie is centered where it is supposed to be
• Page 2: 1433 Tone . gpu06
• Same plots as page 1. The 1433 is sitting in the correct channel
• There is no aliased birdie .. probably because the tone is not close to the edge.

Summary:

• Running puppi with a clock of 213 MHz in baseband mode gave the correct results for two birdies in different gpu's..
  
• So the frequency center and the span is correct
• The birdie close to  the edge of a gpu channel showed appreciable aliasing in the pfb channel. I wonder if this is normal , or the increased clock caused this?
  

processing: x101/160927/puppitest.pro