Links:

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The model parameters:  (top)

1. Convert from the astronomical coordinate system (ra,dec) to az, za.
2. Evaluate the model correction function at this az, za.
3. Add the model correction to the az,za computed in 1. Since the model correction is in great circles, you must divide the azimuth model correction by  the sine of the zenith angle before adding it to the azimuth value computed in step 1.
4. Evaluate the encoder tables for az,za at the current za and add these values to that in 3.

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The model parameter values by receiver.   (top)

327
430dome
430ch
610
lbw (1.2 to 1.75 Ghz)
sbw (1.8 to 3.1 Ghz)
sbn (2.3 to 2.4)
sbh (3 to 4 )
cb   (4 to 6)
cbh (6 to 8)
xb  (8 to 10)

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Pointing models and  measurements:  (top)

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History: (see also: systemhistory)  (top)

• model 0 oct97 -
• used 4 term model: offset, cosaz,sinaz,sinza.
• sband tx receiver with turret at 60.54 degrees.
• Sources from AO catalog (chris salter).
• model 1 dec97 -
• 10 terms. added sin(za)^2, sin(3az), cos(3az), sin(za-bal)*cos(3az) , sin(za-bal)*sin(3az), sin(za*57).
• model 7 jan98 -
• 13 terms. removed sin(za*57), added sin(2az), cos(2az), sin(6az), cos(6az).
• model 8 apr98 -
• switched to sband rx receiver (sband narrow).turret position 60.65 -> 75.0.
• model 9 may98   -
• model 9 sept98   -
• hurricane Georges hits the observatory.
• model 10  jan99 -
•  dome re-alignment.
• sband turret position moved 75 -> 76.6 degrees.
• model 11 feb00  -
• rails reshimmed.
• Horn positions in turret resurveyed by lynn baker.  Sband horn moves 76.6->76.83.
• Use tiedown tracking of the temperature (.2 inches/degF) during model.
• dec00  -
• broken wheels on dome. Dome jacked up and wheels replaced. Jacking beam on azimuth arm 20 feet from main bearing (weight 1000->2000 lbs ??).
• model 12 ,feb01-
• switched to idl for processing.
• Sampling went 100ms -> 10ms so time constant doesn't affect measurements as much.
• Model data taken only during the day (10am to 6pm).
• The reflector surface above the main cables had just been adjusted.
• Started including NVSS sources.
• Tiedown tracking of average platform height (using the distomats) while the model was taken.
• Pointing pre-processor running to smooth out motions
• This model was never installed and used.
• 19/21sep01 sband wide receiver back on turret.
Sbw receiver back up on turret after over a year of "not working". Did 2 strips on B1442+101 using turret scans and heiles calibration patterns. see plot
Changed za  model offset -70 ->-90 asecs (now the same as the sbn).
 (see x101/010921/doit.pro)
• jan02, model13
• Model made using sband calibration data (heiles scans) from Sep01 thru jan02 and from turret scans in dec01 and jan02.
• The reflector adjustments finished in sep01.
• The model was made relative to model 11 (model12 was never installed).
• The tiedowns were running for the entire time.
• feb02 model13 installed for xband pointing
• 22mar02 model13 installed for sbh with sbn offsets.
• aug02    felipe tightened the small rollers on the dome right side. now about 1/32" play. was 1/4 to 1/2"
• 15sep02 az encoder jumped. added offset of -1446 to the az term of the sinza coef. did it for all models except carriage house.

02dec02 the new trolleys weigh about 3000 lbs more than the old ones. Pointing is changing vs za because of it.
• 01mar03 model 14

    data taken 01mar03->03mar03 after shimming elevation rails, and moving dome up 1.65 inches.
• 04mar03 model 14 installed with old horn offsets.
• 7mar03. verify of other horns, offsets added to model14 for each receiver 18:00.(except 327,610,430 needs to be done).
• 14may04: model 15 completed installed sbn. begin verify other horns.
• 27dec04: cbh. model offsets (az,za) incremented by (-.28, -3.8) asecs. from x102 data.
• 15mar05: model 16 for carriage house made.
• 16dec07: model 17 installed sbn.
  
• apr08: alluminum work platform reinstalled top chord azimuth, ch side 131 feet from center
• 16apr08: work platform 500 lbs
• 23apr08: access ladder for platform 200 lbs
• 20may08: ladder cage 80 lbs.
• 20jun08: updated pointing model with fits to 1az, 3az terms.
• 01jul08: subtracted 4 asecs from xb za constant term for bania's run... (other recievers not modified).
  

 comments:

• Model 9 to model 10 rms jumped up by almost 2 asecs. Hurricane georges was between these two date. The encoder tables don't seem to fit as well. The roller bearings that guide the dome up/down the elevation rails were readjusted. I need to find out if this occured during this period.
• Model 10 to model 11 no encoder table values jumped down in za by about 6 asecs. This was because the reshimming of the elevation rails brought them closer to the model fit. The overall fit with the encoder table included actually got worse.
• Model 12 was never installed
• Model 13 was used for a few newere receivers
• Model 14 was made after shimming, and moving the dome.
• Model 15 after kevlar cables and alfa installed. The roller bearings for the dome had been tightened on one side to force the dome to track along that line (the other side was left loose). It looks like this brought us back to the rms that we orignally had in may98 when both roller bearing sides were tight.
• 16dec07 pointing model 17. finished receiver offsets in jan08.
• 21jun08: updated pointing model from 1az, 3az fits to pointing runs. :w

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Misc pointing  info    (top)

The telescope model.

Taking the data using turret scans.

Definition of the sign of the offsets using turret scans or heiles calib scans:

Fitting the data

Verifying the model

Turret positions:The turret positions and the corresponding pointing errors

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