Receiver Agc Signal; Antenna Geo Elevation Position; Configuring The Tracking System; Agc Adjustment And Configuration - RESEARCH CONCEPTS RC2000C Manual

30 RC2000C Polar Tracking Antenna Controller
It is important that the user not change the time value when the time changes from Standard Time to
Daylight Savings Time. The satellite does not experience the time shift. If the time is changed forward or
backward by one hour, the data in the program track table will no longer be correct. For this reason the
user should not change the time as the time standard changes. If this causes confusion the time may be
specified as Greenwich Mean Time (often referred to as GMT). Note that the real time clock used in the
controller will properly account for leap years.
4.3.5

Receiver AGC Signal

To implement the tracking algorithms, the controller requires an input signal which indicates the strength
of the received signal. Such a signal is generated within a satellite receiver, and is referred to as an AGC
signal. (AGC is the abbreviation for Automatic Gain Control.) On satellite receivers, this signal may also
be referred to as a 'Signal Strength' or 'Tuning Meter' output. An AGC output typically varies in proportion
to the received power of the transponder which the receiver is currently tuned to.
The signal strength input is used to peak up the antenna while step tracking. The step tracking operation
positions the antenna so as to maximize the received signal strength. Signal strength is also used to
determine whether or not a satellite transponder is currently active. If the signal strength reading falls
below a threshold set by the user, the controller assumes that a satellite signal is not present. If the
satellite signal is lost while step tracking, the SEARCH sub-mode receives control. When the
PROGRAM_TRACK sub-mode is active, the presence of a satellite signal governs whether or not track
table update operations are performed. The procedures required to set up the controller for various
receiver AGC configurations are covered in detail in the next section.
4.3.6

Antenna Geo Elevation Position

The search region will be centered in elevation at the Geo Elevation Position. This value is entered via
CONFIG mode, and is described in section 3.6. If the user attempts to initiate a track on an inclined orbit
satellite when the Geo Elevation Position has a value of zero, the ERROR sub-mode will activate with '**
ERROR ** GEO' message displayed.
4.4

Configuring the Tracking System

This section describes the procedures which the user must follow to configure the tracking system. The
procedures for adjusting the AGC gain and offset pots, determining the AGC threshold parameters, and
entering other CONFIG mode data pertaining to the tracking system, are all covered in this section.
4.4.1

AGC Adjustment and Configuration

The use of the AGC signal was described in the previous section. The controller has the provision to
process two channels of AGC information. This means that two receivers can be connected to the
controller (at least one receiver is required). The two channels are referred to as AGC1 and AGC2. The
controller uses the stronger of the two as its AGC input. Each channel has separate gain and offset
potentiometer adjustments. The installer uses the pots to transform the receiver's AGC signal swing into
a range of values which is easily measured by the controller.
In addition to the potentiometers, there are three CONFIG mode items which are related to the AGC
system. The three items are ...
1. AGC Polarity Flag - This flag indicates to the controller whether a stronger satellite signal
corresponds to a higher AGC voltage (positive polarity) or a lower AGC voltage (negative polarity).
Both AGC channels must have the same polarity. Each AGC channel contains an internal pull down
resistor. This means that if one of the AGC channels is unused, its input is pulled to ground. This
can cause problems if the AGC Polarity Flag specifies negative polarity, because an input of zero
volts (ground potential) corresponds to the strongest possible satellite signal. For this case the
installer must place a jumper from connector J1, pin 11, to the unused AGC input channel and adjust
that channel's potentiometers (after negative polarity has been specified) so that its signal strength
value is 0. J1 - pin 11 has a potential of 5.7 volts.
2. AGC C Band Threshold - When the receiver is tuned to a C band satellite and the signal strength is
above this value, it is assumed that a satellite signal is present. The same threshold is applied to
both AGC channels.
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Chapter 4 Inclined Orbit Satellite