Motions and angles

aug17

in the focal plane
how big can ao40 be
pointing errors.

In the focal plane:

Plate scales:

from german's alfa memo page 37 (atoms 2001-03.pdf)
x axis in za direction. Positive is away from secondary
y axis perpendicular to az arm. Positive it toward the stairwell
z axis in along focus. Positive is pointing toward

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 18.42 asecs/cm			x along za direction positive pointing downhill
x>0 42.21 asecs/inch 16.62 asecs/cm
y 37.08 asecs/inch 14.60 asecs/cm			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 = 3.241 cm =47.3 asecs on sky = 45 asecs on sky (from measurements)			(1)!dtor73.125=1.276 inches 1.276*37.08secs/in=47.3 asecs on sky 45 asecsSky/degTur comes from measurements on sky.
horn position
ft	in	cm
	70.48	179.02	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).
	69.41	176.30	radius for center of horn on floor (alfa/ao40) germans 1.07" offset
8.11 degrees			horn angle relative to floor perpendicular, tilted so horn is closer to secondary.
	18.75	47.63	vertical distance top of floor to horn phase center.
	73.151	184.34	radius center of floor to horn phase center 70.48 + 18.75*tan(8.11) inches
	70.611	179.35	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)
turret floor			from gregorian upgrade drawings page s-42. More recent measurements show slightly different values...
ft	in	cm
8' 7.75"	103.75	263.53	radius of rotary floor
50deg 40deg			pi sections on the floor they alternate 50deg,40deg
4' 6.5"	54.4	138.47	diameter 50 deg wedge opening
6' 4.75"	76.75	195.00	radius center of 50 deg wedge opening (radiusFloor - 1/2 opening diameter)
3' 6"	30	106.71	diameter 40 deg wedge opening

Notes:

be a little suspicious of the 73.125 inches radius for the horn focal point. This assumes the feed tower was not changed at all when kevlar cables installed. Better to look at where the coma lobes show up.

Trying to figure out how big ao40 can be:

Assumptions:

radius of floor 263.53 cm
radius of c channel around lower edge of floor 2.26"= 5.74cm
Radius to use when lowering ao40 through the floor (to clear the c channel): 263.53- 5.74=257.8 cm
radius for center of horn mount on the floor:

single pixel: 70.48" (179.02 cm)
alfa/ao40: 69.41" (176.30 cm) This includes german's 2.72 cm offset (inward on the radius).

Assumptions:

the opening diameter goes from the edge of the floor to the cross beam of the pi wedge without hitting the pi wedge Ibeams..
Use 257.8 cm for the floor radius (so you don't hit the c channel around the inner edge of the floor).

Diameter of Hole Opening cm	Radius on floor @center of opening cm		Radius on floor for Focus mount cm	Opening Center to floor Focus mount cm	useable Diameter cm	Source of opening diameter
138.47	188.6	std	179.02	9.55 radially in	119.37	upgrade drawing
138.47	188.6	with -2.72cm offset	176.30	12.27 radially in	113.93	upgrade drawing
142.0	186.8	std	179.02	7.78 radially in	126.44	ao40 report
142.0	186.8	with -2.72cm offset	176.30	10.5 radially in	121.0	ao40 report

We tried checking these numbers by measuring the wedge holding alfa, relative to the edge of the rotary floor
The image shows the measurement results:
alfa wedge location

If we assume that the alfa focal radius is at the center of the wedge (either the top or the bottom of the wedge) then we can
compute what the radius for the center of alfa on the floor should be. (more info) This will check if the floor radius, focal radius used above are correct.
I just subtracted the center of the wedge from the floor radius to get the mount location on the floor.
For these computations use 264.23 cm for the floor radius since the above measurements were made from the top of the floor (the c channel was not in the way).

flrRad cm	Floor Radius @ wedge Center cm	Floor Radius for focus mount		alfa Wedge Center to german's offset focus on floor	notes
flrRad cm	Floor Radius @ wedge Center cm	normal	with German's 2.72 cm downhill offset	alfa Wedge Center to german's offset focus on floor	notes
264.23	176.26	179.02	176.30	.04 cm radially out	assume bottom of wedge centered
264.23	177.92	179.02	176.30	1.1 cm radially in	assume top of wedge centered and 8.17 deg tilt moves 1.65 cm radially out

So using the bottom of the alfa wedge as the center, we get the canonical horn floor focal radius fir multibeam feeds.

AO40Summary

Using the bottom center of the alfa wedge as the floor radius to position alfa and assuming:

the floor radius : 264.23 cm

We get:

179.02 cm floor radius for single pixel focus.
176.30 cm floor radius for multi beam (alfa,ao40) focus

Forcing ao40 to be centered at one of the focii gives a useable opening diameter of :

opening diameter cm	allowable diameter using singlePixFocus cm	allowable diameter using multiBmFocus cm
138.47	119.37	113.93
142.0	126.44	121.0

We should probably see how many cm there is between the edge of alfa and the constraining beams.

When installing ao40, it will be lowered through the floor, and then tilted by 8.11 degrees. This let s the inner part of ao40 pass underneath the inner cross beam of the floor pi wedge support.

pointing errors

model values get added to the computed az,za
pointing errors from cross scans should be subtracted from az,za used
pointing errors from turret scans should be added to the az,za used.







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