Motions and angles



In the focal plane:

az,za vs focal plane motions
moving horn uphill
same as moving dome uphill
moving horn ccw (toward stairwell)
  • increases turret angle
  • same as moving azimuth CCW (to a lower azimuth angle)
plate scales
x<0 46.79 asecs/inch
 x along za direction
positive pointing downhill
x>0 42.21 asecs/inch
y 37.08 asecs/inch
y perpendicular to az arm
positive pointing toward stairwell
turret motion
increasing turret angle
moves horn from focus  toward the stairwell (+y direction).
same as moving azimuth CCW (to lower angle)
moving turret 1 deg:
=1.276 inches
=47.3 asecs on sky
= 45 asecs on sky (from measurements)
(1)*!dtor*73.125=1.276 inches
1.276*37.08secs/in=47.3 asecs on sky

45 asecsSky/degTur comes from measurements on sky.
horn position
70.48 inches
radius for center of horn mount (on the floor).
Assumes feed tower position relative to the 2ndary did not changes after kevlar cable installation (2004).
8.11 degrees
horn angle relative to floor perpendicular,
tilted so horn is closer to secondary.
18.75 inches
vertical distance top of floor to horn phase center.
73.125 inches
radius center of floor to horn phase center
70.48 + 18.75*sin(8.11) inches
70.611 inches
scribe mark on rotary floor.
motion of coma lobe
moving horn uphill (away from optical axis) creates coma lobe in - za direction
  • in spider scan, shows up in -za offset.
moving horn CCW (away from optical axis, increasing turret degree) causes coma lobe in + azimuth direction of beam map (see alfa beam maps)


pointing errors