PROTOTYPE ANTENNA TESTS
This was presented at the MMA PDR on July 28 1998. It is a
first draft of tests proposed for the first MMA prototype antenna,
at the US continental test site. Darrel Emerson.
- ON THE FIRST ANTENNA, BEFORE SECOND ANTENNA BECOMES AVAILABLE
NRAO Installation of:
- Thermistors
- Tilt meters
- Control interfaces
- Optical telescope, CCD camera
General checks:
- General mechanical inspection, wiring checks
- Mechanical operation: brakes etc.
- Interface integrity
- Mechanical slew rate check
- Mechanical tracking check
- Surface setting check (theodolite?)
- Tiltmeter checks of azimuth rotation
Antenna dynamic (mechanical) response:
- Resonant frequencies, accelerations
- Check motor currents, bearing friction, power consumption
when slewing & tracking
- Weather-proof?
Monitoring:
- Start systematic monitoring of temperatures, tilt meters,
motor currents, ambient conditions (wind, temperature ...)
First tracking and pointing tests:
- Optical pointing measurements
- Needs CCD, interfaces, computer + software
- Needs simple interface to telescope drive system (computer?)
- Simple servo tests:
- Move to star, slew away, slew back:
- Servo response, oscillation?
- Tracking tests:
- Track edge of moon, stars ...
-
Optical Pointing checks
- Measure pointing offsets on > mag 5 stars
- First astronomical pointing model
- Consistency of pointing (night to night, temperature,
wind ...)
Electromagnetic measurements:
- Prime Focus Holography.
Initial Requirements:
- Requires pointing and tracking understood,
- Control system interface,
- Holographic system, frontend and backend,
tested out.
- Holographic reference feed measured
- Integrated holographic data acquisition,
telescope pointing
- Observing modes tried and tested
- Holography data analysis system available
- Terrestrial holographic measurements
- Beacon on nearby mountain (90 GHz?)
- Repeat until no longer useful:
First holography maps: 129*129, 10-cm resolution
Repeat, check for repeatability
ADJUST SURFACE.
Derive efficiency
End repeat
- IF POSSIBLE:
- Deformations as function
of elevation.
-
Using 90 GHz/230 GHz, secondary focus receiver
- Needs nutating subreflector
- Measure radio pointing (mainly planets).
- Reconcile radio/optical pointing
- Derive radio pointing model. Check for consistency, stability.
- Check radiotracking (edge of moon, edge of Jupiter)
- Measure efficiency at 230 GHz:
Radiometrically, planet
- Measure error pattern (e.g. sensitive beam map on planet,
moon scan).
- Measure forward and rear spillover, variation with elevation?
(Hot/cold calibration, sky tips)
- Reconcile holographic measurements with radiometric,
efficiencies and error pattern measurements
- Using 230 GHz measurements, confirm fast switching characteristics
- Surface deformation with elevation:
Problem. Error pattern? Beam shape?
(Satellite availability?)
-
Reproducibility after transportation
Tilt meters? New pointing determination needed?
- Confirm that solar observations are possible
(Heating, panel IR scattering, pointing)
- Subreflector.
- Is a nutating subreflector needed?
- Compare point source measurements,
OTF maps, with and without nutating S/R.
- Spectral purity:
- Stability of baselines,
- Standing waves.
(Requires spectrometer.)
- WITH SECOND ANTENNA: INTERFEROMETER TESTS
(Can some of these be done before 2nd antenna available?)
- Are we SURE about close packing limitations?
- Phase stability (lateral displacements, wind, bearing slop)
- Phase stability while fast switching? (Structure oscillations?)
- More extensive radio pointing tests now possible
- Interferometric Holography:
- Using 86 GHz SiO maser (needs spectral correlator) and/or
planets.
- Needs complete interferometric, phase stable, fringe tracking,
delay tracking electronics.
- Measure surface (e.g. 48*48) deformations as function of elevation.
-
General correlations:
- Use archived weather (wind, temperature, gradients ...)
data to look for correlated effects on antenna (surface
deformation, pointing ...)