Research Concepts RC2500 - Manual (Page 63)

56 RC2500 Antenna Controller Chapter 5 Modes
Research Concepts, Inc. • 5420 Martindale Road • Shawnee, Kansas • 66218-9680 • USA www.researchconcepts.com
1. The Max Track Error parameter is set to a 'low' value which results in an elevation peakup step size
of just one position count.
2. When a peakup occurs, the controller measures the signal strength at the current antenna position,
and then moves the antenna up or down in elevation in an attempt to find the strongest satellite
signal. After recording the signal strength at the starting position, the controller moves the antenna
up in elevation by one position count.
3. Due to mechanical hysteresis, the antenna's pointing angle does not change even though the
antenna's elevation resolver has moved one position count.
4. Thermal noise in the receiver's AGC circuit or changing atmospheric conditions result in the controller
measuring a stronger AGC input at the 'new' antenna position.
5. Since a stronger signal was measured when the antenna moved up, the controller concludes that the
satellite has moved up. The controller will record the signal strength at the current antenna position,
and again move up by one position count. At the new position, the controller will measure the signal
strength again to determine if the signal is stronger at the new position than at the starting position.
This process will continue until a weaker signal strength is recorded. When that occurs, the controller
will back up one step and conclude that it has found the elevation peak.
6. A problem occurs if the controller makes the wrong decision at step 4. Any time the controller step
size is comparable in magnitude to the antenna's mechanical hysteresis, a problem WILL eventually
occur.
For most antennas the MAX TRACK ERROR should not be made smaller than 5 (0.5 dB). The
fundamental ability of an antenna system to track a satellite will depend to a large extent on the
mechanical characteristics of the mount.
5.8.10.2 SEARCH ENABLE
SEARCH ENABLE:1 CONFIG
0-DISABLE, 1-ENABLE ENT,BKSP,SCRLL ^v
The SEARCH ENABLE CONFIG mode item specifies whether or not the Intelli-Search algorithm is
enabled or disabled. When the STEP TRACK submode is active and the signal strength input indicates
that the satellite transponder has gone down, the controller will switch to the SEARCH sub-mode. The
SEARCH ENABLE CONFIG mode item is the controlling item for the SEARCH WIDTH CONFIG mode
item which is described next.
If the SEARCH ENABLE CONFIG mode item is enabled, the controller will execute the Intelli-Search
algorithm. During an Intelli-Search, the controller will perform a serpentine-shaped search over a region
where the controller has calculated that the satellite's apparent motion will take it. If the satellite is not
found during the Intelli-Search, the search is periodically repeated until either signal strength information
is available, or track table information becomes available.
If the SEARCH ENABLE item is disabled, the user is simply prompted to manually position the antenna
on the satellite and hit the ENTER key to continue. The Intelli-Search should be disabled for transmit
applications. It may also be advantageous to disable Intelli-Search for antennas which move very slowly.
5.8.10.3 SEARCH WIDTH
SEARCH WIDTH:3 CONFIG
1-10, NOMINAL=3 ENT,BKSP,SCRLL ^v
The SEARCH WIDTH item controls the width of the sweeps that occur during execution of the Intelli-
Search algorithm. If the angular extent of the sweeps is too large, the controller could mistakenly align
the antenna with an adjacent satellite. A search with narrow sweeps takes much less time to complete,
but may not sweep over a region which is wide enough to find the satellite.
The SEARCH WIDTH is not an absolute value - increasing its value results in wider sweeps, and
decreasing its value narrows the sweeps. The actual pointing angle over which search sweeps occur is a
function of the antenna beamwidth and the SEARCH WIDTH parameter. For a given SEARCH WIDTH