RESEARCH CONCEPTS RC1500B Manual page 4

result was obtained from the publication Inclined Orbit Satellite Operation in the Intelsat System
written by Rory Chang and Les Veenstra, revised July 1991.
Many people make the mistake of plotting satellite azimuth vs. elevation and obtaining an
'angle' by looking at the ratio of azimuth to elevation movement. The problem with this
approach is that at elevation angles greater than zero, one degree of azimuth movement does not
change the antenna pointing angle by one degree. When antenna elevation angle is 90 degrees,
changing the antenna azimuth angle does not change the antenna pointing angle at all (it does
change the polarization, however).
RC1500.XLS Spreadsheet
A spreadsheet has been developed that performs a number of calculations related to single axis
tracking.
The spreadsheet takes as its inputs...
1. Antenna operating frequency and diameter,
2. Satellite longitude and inclination. Inclination of the satellite's orbital plane with respect to
the earth's equatorial plane. This data can sometimes be obtained from www.lyngsat.com
(select a satellite, from the satellite page select Sat Tracker, a summary of satellite info is
given) or from a two line element (TLE) set – see 'Setting Up a Single Axis Tracker', step 1,
for the data format of a TLE set.
3. Earth station latitude/longitude
Given this information, the spreadsheet calculates the following quantities...
1. Antenna 3 dB beamwidth (in degrees),
2. Height and width of the figure eight pattern of the satellite's apparent motion (the height and
width are the angular extent of the satellite's motion in degrees),
3. The maximum signal loss (in dB) due the single axis tracker's inability to compensate for the
width of the figure eight pattern.
4. The tilt of the control axis (in degrees)
The spreadsheet uses a parabolic function to characterize the relationship between antenna
angular misalignment and signal loss. The spreadsheet also calculates signal loss given antenna
pointing error and vice versa.
RC1500B Tracking Algorithms
The apparent motion of an inclined orbit satellite repeats itself every 23 hours, 56 minutes, and 4
seconds. The tracking scheme used in the RC1500B employs a step track algorithm to build up a
track table which logs the satellite position versus time ( a real time clock powered by a lithium