Research Concepts RC2000C - Manual (Page 43)

RC2000C Az/El Tracking Antenna Controller Chapter 4 Inclined Orbit Satellites 35
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The user has the option of providing the controller with a value for the azimuth scale factor via the Azim
Constant CONFIG mode item. If the user does not provide a value for the Azim Constant item, the
controller will determine one based on the locations of geostationary satellites (with sufficient
separation) in the vicinity of an inclined orbit satellite that the user wishes to track.
Normally, the user should let the controller determine the scale factor. The user must specify an
azimuth scale factor if it is impossible to program a pair of geostationary satellites into the controller's
memory. The Azim Constant CONFIG mode item should be set to 0 to specify to the controller that it
should calculate the scale factor. If the Azim Constant is set to a non-zero value, that value is used as
the azimuth scale factor.
If is necessary for the user to specify the azimuth scale factor, there are a couple of methods available
to determine the proper value. The most straightforward method is to obtain the azimuth axis 'degrees
per position pulse' value from the antenna manufacturer. Please refer to the discussion above on
determining the elevation scale factor based on antenna manufacturer's specifications. The procedure
for obtaining the azimuth scale factor from the manufacturer's data is identical to the procedure outlined
for the elevation axis.
An instance of when it is not possible to program a pair of geostationary satellites (and the appropriate
information may not be available from the manufacturer) may occur for a weather satellite where there
are not 2 geostationary satellites available at the weather satellite frequency. It is still possible to
determine the scale factor if satellite pointing data is available for a similar antenna mount and actuator
set. Here, satellite pointing data refers to azimuth position counts for a pair of geostationary satellites at
known longitudes. If the position counts were not obtained with an RC2000, the user must determine
whether the controller used to obtain the data accumulates position pulses or position pulse edges (as
the RC2000 does). Multiply position pulse data by two to obtain position count data - see the
discussion above on obtaining the elevation scale factor from manufacturer's data for the distinction
between position pulses and position counts. The following calculation yields an approximate value for
the azimuth scale factor that generally gives adequate results.
In the following formula the position count and longitude associated with the first satellite is designated
CNT_1 and LON_1, respectively. The position count and longitude value associated with the second
satellite is referred to as CNT_2 and LON_2.
Here is the formula... ( (CNT_1 - CNT_2) / (LON_1 - LON_2) ) * 48
Round to the nearest whole number and convert negative numbers to positive numbers. Note that in
the denominator of the above expression (LON_1 - LON_2) refers to the difference in longitude values
between the two satellites. If LON_1 has a value of 5 degrees West and LON_2 has value of 7 degrees
East, then (LON_1 - LON_2) is 12 (= 7 + 5). If westerly longitude values are treated as negative
numbers the formula works fine.
((_______ - _______) / (_______ - _______)) * 48
= _______ (counts per radian)
Change the sign to convert to a positive value. Enter at the Azim Constant CONFIG mode prompt.
Here is an example...
azimuth position count longitude
satellite 1 1520 7 degrees West
satellite 2 944 5 degrees East
Here is the calculation...( (1520 - 944) / (-7 - 5) ) * 48
simplifying yields ( (576) / (-12) ) * 48 = (-2304)
4.4.3 CONFIG Mode Data
This section briefly describes each of the CONFIG mode items and how they relate to the tracking
system. The names of CONFIG mode items appear in italics. The installer should go through this