RC3000 Antenna Controller | Chapter 2 | Installation |
2.4.4 Pulse Scale Factors
The pulse scale factors specify the number of pulses counted per degrees (in radians) of movement for the azimuth and elevation axis. It is critical that these numbers are accurate since the tracking algorithms use them to determine step sizes (in pulse counts). Note that the RC3000 counts both rising and falling edges of the position pulses so that a single position pulse generates 2 position counts.
NOTE: In the majority of cases, the antenna scale factors will have already been characterized for a mount and the appropriate values stored as defaults. The following procedures will only be required if a condition exists (different gear ratios, different pulse sensors, etc.) exists.
The azimuth and elevation scale factors may be derived from the antenna mount manufacturer’s data or from data measured by moving the mount.
SCALE FACTORS FROM MANUFACTURER’S SPECIFICATIONS
If the antenna manufacturer gives the position pulses per degree specification for the antenna’s azimuth and elevation axis, simply multiply the value by 2 to obtain 'position counts per degree' (because the RC3000 counts both the rising and falling edges of the position pulses). Multiply this 'position counts per degree' value by 57.29 to obtain 'position counts per radian'. Round to the nearest whole number value to obtain the Elev Constant CONFIG mode item.
Elev position pulses per degree _______ * 2 * 57.29 = _______ (position counts per radian)
SCALE FACTORS FROM MOUNT MEASUREMENTS
The elevation scale factor is obtained by 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.
Here is the procedure:
Step 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.
Step 2. Record the elevation position count and the reading of the inclinometer. These will be designated CNT_1 and DEG_1, respectively.
Step 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.
The elevation region over which the measurements are made should correspond to the range of elevation angles which will be encountered in operation (i.e. the elevation values over which the satellites will be found).
Step 4. Use the following formula to calculate the Elev Constant:
( (CNT_2 - CNT_1) / (DEG_2 - DEG_1) ) * 57.29
If the result is negative, change the sign to positive. Here is an example:
| Inclinometer | Pulse |
| Angle | Count |
Higher Position | 50.2 | 32768 |
Lower Position | 29.8 | 541 |
Difference | 20.4 | 32227 |
(32227 / 20.4) * 57.29 = 9062 pulses/radian
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