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lbaops:daspulsarprocedures [2016/01/04 19:44]
cormac
lbaops:daspulsarprocedures [2016/01/07 13:44] (current)
cormac
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-Procedure for disabling DAS gain and threshold loops for pulsar observing+===== Procedure for disabling DAS gain and threshold loops for pulsar observing ​=====
 ------------------------------------------------------------------------- -------------------------------------------------------------------------
  
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 any pulsar signal; any pulsar signal;
  
-  ​- the GAIN loop : a voltage-controlled amplifier ahead of the sampler, servo'​d to maintain constant 8-bit sampled amplitude. +<​file>​ 
-  - the THRESHOLD loop operating on the digitally filtered data to keep the statistics of the 2-bit output data fixed (usually at 34.6%). This loop operates in a stepwise fashion, resetting the thresholds on a fixed cycle which depends on filter bandwidth. For 16MHz filters the cycle is 2^19 samples = 33ms.+        ​-the GAIN loop : a voltage-controlled amplifier ahead of the 
 +         sampler, servo'​d to maintain constant 8-bit sampled amplitude. 
 + 
 +        ​-the THRESHOLD loop operating on the digitally filtered data 
 +         to keep the statistics of the 2-bit output data fixed (usually ​ 
 +         at 34.6%). This loop operates in a stepwise fashion, resetting ​ 
 +         the thresholds on a fixed cycle which depends on filter ​ 
 +         bandwidth. For 16MHz filters the cycle is 2^19 samples = 33ms. 
 +</​file>​
  
 (At Narrabri there is no GAIN loop in the DAS. In the Pre-CABB era the  (At Narrabri there is no GAIN loop in the DAS. In the Pre-CABB era the 
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 by Simone Magri and Mark Leach). by Simone Magri and Mark Leach).
  
-Procedure for GUI Version of control software: +=== Procedure for GUI Version of control software: ​===
-----------------------------------------------+
  
- 1. Wait till you're on source (or levels are stable), then adjust the pre-DAS attenuation to centre the "​LEVEL"​ bargraph/​slider on each IFP.+---------------------------------------------- 
 +<​file>​ 
 + 1. Wait till you're on source (or levels are stable), then adjust the 
 +    ​pre-DAS attenuation to centre the "​LEVEL"​ bargraph/​slider on each  
 +    ​IFP.
  
  2. Select "​Detail"​ under "​Monitor view".  2. Select "​Detail"​ under "​Monitor view".
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  ​6. ​ Hit "​Config_Hdw"​ to upload the revised configuration to the DAS.  ​6. ​ Hit "​Config_Hdw"​ to upload the revised configuration to the DAS.
  
- ​7. ​ On the "​Detail Monitor view" display you should now see for each IFP:+ ​7. ​ On the "​Detail Monitor view" display you should now see for each  
 +     IFP:
  
      ​Level ​ : 128 Manual      ​Level ​ : 128 Manual
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      where the values 128 and 72 might be varying by +/- a few.      where the values 128 and 72 might be varying by +/- a few.
  
- 8. Check that the stats on your VLBI recorder look normal (34.6% of samples in the two outer bins combined).+ 8. Check that the stats on your VLBI recorder look normal (34.6% of 
 +    ​samples in the two outer bins combined).
  
     Throughout the observation,​ monitor the "​level"​ numbers for each IFP     Throughout the observation,​ monitor the "​level"​ numbers for each IFP
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     close as possible to 34.6%. These numbers are in ~0.1dB     close as possible to 34.6%. These numbers are in ~0.1dB
     steps, so if the lvl drops to say 123, remove 0.5dB to centre it.     steps, so if the lvl drops to say 123, remove 0.5dB to centre it.
 +</​file>​
  
 +=== Procedure for DOS version of control software ===
  
-Procedure for DOS version of control software 
 --------------------------------------------- ---------------------------------------------
 +<​file>​
 + 1. Wait till you're on source (or levels are stable), then adjust the
 +    pre-DAS levels/​attenuators to centre the "​LEVL"​ bargraph on each IFP.
  
- 1. Wait till you're on source (or levels are stable), then adjust the pre-DAS levels/​attenuators to centre the "​LEVL"​ bargraph on each IFP. + 2. Hit the space bar to view the alternate monitor display. 
- +    ​For IFP #1, observe and note the average value of the three numbers 
- 2. Hit the space bar to view the alternate monitor display. For IFP #1, observe and note the average value of the three numbers "​lvl"​ and "​cntX"​ and "​cntY"​ as shown below;+    ​"​lvl"​ and "​cntX"​ and "​cntY"​ as shown below;
  
     LEVL: lvl C    <== lvl       ​OFFS: ​  0 C     LEVL: lvl C    <== lvl       ​OFFS: ​  0 C
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       where the actual values 128 and 72 might be varying by +/- a few.       where the actual values 128 and 72 might be varying by +/- a few.
  
- 7. Hitting the space bar to return to the default display you should now see "​Monitoring Only" for "​IF"​ on both IFPs The associated bargraphs should all be centred.+ 7. Hitting the space bar to return to the default display you should now 
 +    ​see "​Monitoring Only" for "​IF"​ on both IFPs 
 +    ​The associated bargraphs should all be centred.
  
  8. Check, monitor and adjust sampling stats, as for GUI version above.  8. Check, monitor and adjust sampling stats, as for GUI version above.
  
 +</​file>​
  
 JER JER
lbaops/daspulsarprocedures.1451897097.txt.gz · Last modified: 2016/01/04 19:44 by cormac