Initializing The Antenna Scale Factors - RESEARCH CONCEPTS RC2000C Manual

34 RC2000C Polar Tracking Antenna Controller
transponders, gain flatness problems could also cause the controller's AGC input scaling network to be
saturated when the antenna is aligned with a strong satellite, making it impossible for the controller to
detect changes in signal strength when attempting to peak the antenna.
To test the gain flatness of the satellite receiver, perform the following procedure. The procedure
assumes a single receiver, single frequency band system.
1. Position the antenna well off of any satellite. Tune the receiver to each transponder. Make sure that
the signal strength reading is below the threshold assigned via CONFIG mode.
2. Align the antenna with a strong satellite. Tune the receiver to each active transponder on the
satellite. Make sure that the signal strength is well above the threshold and below 999.
If the system fails either of the tests above, then the user can either attempt to correct the problem by
readjusting the GAIN and OFFSET pots (using the procedure outlined earlier), or by correcting the gain
flatness problem. Most gain flatness problems can be traced to a problem with the coaxial cable
connecting the antenna to the receiver (sometimes called a 'suck-out') or to bullet amplifiers. Some bullet
amplifiers have been observed to have really terrible gain flatness characteristics.
To perform the above tests on a dual frequency band system, repeat the test for each frequency band.
On a dual receiver system, simply perform the test on each receiver. On a dual frequency system the
tests should be performed with the controller in LIMIT mode, so that there is no confusion as to which
AGC input channel the displayed signal strength reading corresponds to.
4.4.2

Initializing the Antenna Scale Factors

The azimuth and elevation scale factors refer to the mapping of antenna azimuth and elevation position
counts to antenna azimuth and elevation angles. The elevation scale factor is entered by the user. The
azimuth scale factor can either be specified by the user, or it can be derived from the position and
longitude data of adjacent geostationary satellites. The antenna scale factors are specified via the Azim
Constant and Elev Constant CONFIG mode items.
The Azim Constant and Elev Constant items are specified in position counts per radian. A radian is a unit
of angular measure. 2 times PI radians equals 360 degrees where PI is equal to 3.1415. To convert
degrees to radians, multiply the degree value by 0.0174532. To convert radians to degrees, multiply the
radian value by 57.295. Note that the RC2000 counts both rising and falling edges of the position pulses
so that a single position pulse generates 2 position counts.
Elevation Scale Factor
This section describes the method used to determine the elevation scale factor needed to initialize the
Elev Constant CONFIG mode item. The method is based on moving the antenna in elevation over a
known angle (as determined by an inclinometer) and obtaining the number of counts which corresponds
to the angular movement. A hand calculator is then used to determine the Elev Constant.
Here is the procedure:
1. Identify a location on the antenna to place the inclinometer. The location on the mount should be
selected so that one degree of movement about the elevation axis registers as one degree on the
inclinometer. It is best to use an inclinometer which has a magnetic base. These are available in
hardware stores.
2. Record the elevation position count and the reading of the inclinometer. These will be designated
CNT_1 and DEG_1, respectively.
3. Jog the antenna in elevation. It is recommended that the antenna be moved 15 to 20 degrees in
elevation. Record the elevation position count and the inclinometer reading. These will be
designated CNT_2 and DEG_2.
Research Concepts, Inc. • 5420 Martindale Road • Shawnee, Kansas 66218-9680 • USA www.researchconcepts.com
Chapter 4
CNT1_______ DEG1_______
CNT2________ DEG2_______
Inclined Orbit Satellite