NRAO Home  >  Green Bank  |  Wiki Topic:    GB > Operate > TelescopeOperations > Pointing
   Changes | Index | Contents | Search | Go

TELESCOPE OPERATIONS

POINTING

General

Pointing and the use of Local Pointing Corrections (LPC's) ensure the antenna is pointed accurately at the intended source. Pointing should be accomplished often enough to counter the affects of changing elevation. The need for pointing becomes increasingly import at higher observing frequencies. The observer will determine how often to "point" and the actual settings required. Since every observer has their own methods and preferred setups, this guide only provides general information to assist the operator.

Receiver Information Useful to Determine Pointing Parameters

Receiver - FSky (GHz) Center Frequency (GHz) Wavelength (cm) Half Power Beamwidth HPBW (arcmin) Beamwidth Range (arcmin)
L-Band (1.15 - 1.73) 1.45 21 9 10.43 - 6.94
S-Band (1.73 - 2.6) 2.16 14 5.8 6.94 - 4.62
C-Band (3.95 - 5.85 4.9 6.1 2.5 3.04 - 2.05
X-Band (8.0 - 10.1) 9.0 3.3 1.4 1.5 - 1.19
Ku-Band (12.0 - 15.4) 13.7 2.2 .9 1.0 - .78
K-Band 1 (18.0 - 22.5) 20.0 1.5 .62 .67 - .53
K-Band 2 (22.0 - 26.5) 24.2 1.2 .5 .55 - .45
Q-Band (40.0 - 52.0) 46.0 .65 .27 .3 - .23

Handy Formulas

Half Power Beamwidth (HPBW) for the GBT = 12.4 arcmin/ Freq (GHz) or 740 arcsec/ Freq (GHz)

Scan Length for Pointing = 8-10 x HPBW (arcmin)

Scan Rate for Pointing = 2 x Scan Length (arcmin)

Estimated GO Settings for Pointing (Based on 8 x HPBW (arcmin) for determining Scan Length)

Receiver - FSky (GHz) Scan Length (arcmin) Scan Rate (arcmin) Switch Period (sec)
L-Band (1.15 - 1.73) 72 144 .02
S-Band (1.73 - 2.6) 46 72 .02
C-Band (3.95 - 5.85 20 40 .02
X-Band (8.0 - 10.1) 11 22 .02
Ku-Band (12.0 - 15.4) 7 14 .02
K-Band 1 (18.0 - 22.5) 5 10 .02
K-Band 2 (22.0 - 26.5) 4 8 .02
Q-Band (40.0 - 52.0) 2 4 .02

Estimated GO Settings for Pointing (Based on 10 x HPBW (arcmin) for determining Scan Length)

Receiver - FSky (GHz) Scan Length (arcmin) Scan Rate (arcmin) Switch Period (sec)
L-Band (1.15 - 1.73) 90 180 .02
S-Band (1.73 - 2.6) 58 116 .02
C-Band (3.95 - 5.85 25 50 .02
X-Band (8.0 - 10.1) 14 28 .02
Ku-Band (12.0 - 15.4) 10 20 .02
K-Band 1 (18.0 - 22.5) 6 12 .02
K-Band 2 (22.0 - 26.5) 5 10 .02
Q-Band (40.0 - 52.0) 3 6 .02

(All computations rounded)

-- DavidRose - 6 Feb 2008

Topic Pointing . { Edit | Attach | Ref-By | Printable | Diffs | r1.8 | > | r1.7 | > | r1.6 | More }
Revision r1.8 - 06 Feb 2008 - 16:50 GMT - DavidRose
Parents: WebHome > TelescopeOperations 		Content copyright © 1999-2007 by the contributing authors.
All material on this collaboration platform is the property of the contributing authors.