GBT-related topics and information

Table of contents

Phase monitor systems
Traditional holography systems
Traditional holography papers
OOF Holography papers
Satellite tracking info
Photogrammetry systems
Inclinometers
Accelerometers
Main Az/El Servo
Links to laser range-finding references
Links to manufacturer's hardware datasheets
Photos
Loral and RSI technical memos
Active surface
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Recent URSI meeting proceedings

pointers to GBT drawings

Existing phase monitor systems:

Existing traditional holography software:

Existing traditional holography systems:

"Traditional" Holography papers:

Related papers

"Out-of-focus" holography papers:

Other methods:

Finding Available Satellites:

Components and datasheets for a broadband system:

R. Kimberk's schematic for the new Mauna Kea phase monitor

Advantanges of a broadband system over a beacon

1. Total power from beacons are weaker: 1-20 dBW EIRP (equivalent isotropic radiated power) rather than 40-50 dBW in the datastream. (Not intended to be picked up by the consumer, some are used for tracking by the service provider. Some are modulated and used for communications.) For comparison, the total power in the SMA 232 GHz beacon on Subaru is about 100nW. If it was isotropic and placed at geostationary altitude (35786km), it would then be 36237km distance from SMA antennas (rather than 200m) and would need to be 3.28 kW = 35 dBW EIRP to provide an equivalent signal (ignoring atmospheric attenuation). In fact, the FWHM of the beacon horn is 9 degree at 232 GHz, which is a gain of 364 = 25.6dB. Thus the EIRP would need to be 60 dBW!

2. Beacon system requires a narrow passband filter (of order 5kHz). For example, the satellite used by the SAO phase monitor drifted out every 30 minutes and computer had to reacquire it via GPIB bus.

3. Beacon system requires downconversion stage from the LNB output (~1 GHz) down to vector voltmeter range (often 500MHz or less). Also, the passband filter is easier to implement at lower frequencies, such as 21 MHz.

4. Beacon system has multiple reflections/standing waves. The broadband system will help wash those out. They manifest themselves in the data as follows: 1) in total power focus scans of the subreflector, one sees oscillations rather than a smooth peak. 2) in the aperture domain, one sees broad radial oscillations (2 or 3 across the dish) in the aperture phase which flip up/down after the subreflector is moved and a new map is made.

Issues Common to Both Systems:
1. The satellites "move" diurnally by 0.02 degrees or so (stationkeeping).

Photogrammetry systems

VLA: VLA test memo 220 (Butler et al. 1999)
Arecibo: NAIC Newsletter from March 2001   CMSC Conference paper, August 2001 (Edmundson & Baker)
APEX: reached 35-40 microns rms with photogrammetry newsletter
SPT: reached 100 microns rms with photogrammetry after first attempt
Hobart 26m: 2005 paper in The Photogrammetric Record v. 20, page 205, local PDF (reached 65um rms on a 26m telescope: 1/400000)
KOSMA: 2003 SPIE paper claims 10 micron measurement accuracy on a 3m dish, but achieved surface rms only 35 microns rms; poster paper
ODIN: reflectors aligned via photogrammetry to accuracy of 50 microns

Inclinometers

Wyler Zeromatic

inclinometers (AG gas-damped capacitive readout)

Servo components

Servo miscellany

Hardware data sheets

Laser range finding references

PTCS references

Tipping radiometer references

Photos

Active Surface