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lbaops:daspulsarprocedures [2016/01/04 19:22]
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: ​===
-----------------------------------------------+
  
 +----------------------------------------------
 +<​file>​
  1. Wait till you're on source (or levels are stable), then adjust the  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      pre-DAS attenuation to centre the "​LEVEL"​ bargraph/​slider on each 
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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  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.     pre-DAS levels/​attenuators to centre the "​LEVL"​ bargraph on each IFP.
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  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.1451895747.txt.gz · Last modified: 2016/01/04 19:22 by cormac