attachment:scan_speed.txt of NikaRun3

   1 At the moment the maximum antenna velocity for tracking a source is 150"/sec. Below that value the tracking error is good, we could say that the error is below 1". At tracking velocities higher than 150"/sec. must be avoided because the antenna switch to another controller less precise (used for large displacements in the sky) and then there is a steady pointing error about 10".
   2 
   3 The previous velocity 150"/sec. is in altazimuth coordinates. Just tracking a source at antenna low elevations implies antenna altazimuth velocities about 15"/sec. This altazimuth velocity increases at high elevations reaching values higher than 150"/sec. at higher antenna elevations than 83 deg.
   4 
   5 If in addition to the own movement of the source in the sky the observer request a scanning velocity, then the maximum antenna elevation must be corrected to avoid exceeding the 150"/sec. The table below resumes how much should be the maximum scanning velocity requested by the observer depending on the antenna elevation.
   6 
   7 > elevation 	max. tracking
   8 > (deg.) 	("/sec.)
   9 > 20 	126
  10 > 25 	121
  11 > 30 	115
  12 > 35 	108
  13 > 40 	100
  14 > 45 	91
  15 > 50 	81
  16 > 55 	71
  17 > 60 	60
  18 > 65 	48
  19 > 70 	36
  20 > 75 	24
  21 > 76 	21
  22 > 77 	19
  23 > 78 	16
  24 > 79 	14
  25 > 80 	11
  26 > 81 	8
  27 > 82 	6
  28 > 83 	3
  29 > 84 	1
  30 Anyway, it is recommended to keep some protective margin with respect to the previous values.