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RC4000 ACU Boardset
Chapter 4
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4.1.11 Signal Strength Adjustment
The RC4000 can sense satellite signal strength via the L-band power detector (2.1.2.4.8) or the signal
strength input circuits
(2.1.2.2.3
or 2.1.2.4.2). This section describes how to configure the signal strength
input circuits for use with the satellite receivers used for a particular installation. Correct adjustment of the
signal strength circuitry is required for autopeak and tracking operations to peak up on a satellite.
4.1.11.1 L-Band Power Detector
The simplest detection scheme is to connect the LNB output to the L-band power detector. For best
results, insert inline attenuation or amplification so that the RF display is approximately 400 when the
reflector is pointed at open sky. The L-band input power detector makes use of a 10-bit ADC labeled
"5-RF" (3.3.2.1.1). See
section 3.3.1.2.6
(Autopeak configuration) for a discussion of the characteristics
of the L-Band power detector.
4.1.11.2 Signal Strength Channel
To implement tracking algorithms and the LOCATE mode's scan/search, 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 to which the receiver is
currently tuned.
Signal strength indications from receivers, modems, etc. vary widely. The RC4000 provides two circuits
that are designed to accommodate any signal strength input that varies between +/- 10 VDC. These
inputs are labeled "REC1" (2.1.2.2.3) and "REC2" (2.1.2.4.2). The REC1 hardware input is routed to the
microcontroller's 12 bit ADC and can be seen in the AD VOLTAGES Maintenance as source "SIG". The
REC2 hardware input is routed to the microcontroller's 10 bit ADC and can be seen in the AD
VOLTAGES Maintenance as source "4-REC2".
Each receiver input is scaled for a -10 to +10VDC range. REC2 can be optionally setup on the circuit
board to accommodate other ranges of input voltages (this type of modification should only be performed
at Research Concepts.)
4.1.11.3 Signal Strength Channel Configuration
The following are guidelines that should be followed when programming the RF/SS1/SS2 SIG FACTORS
screens.
RF SIG FACTORS Refer to
section 3.3.1.2.9
for full details. The "THRES" entry refers to the Minimum
Signal Threshold. The minimum value refers to the minimum difference in signal strength which allows
the antenna controller to confirm that it is pointing to a satellite rather than pointing to open sky.
Example: The RF value is around 300 when pointing to the open sky. It raises to 475 when fully peaked
on a satellite. The value of the RF THRES may be set to 50 to indicate that when the RF strength has
risen from 300 to 350, it confirms that it is on a satellite.
SS1 SIG FACTORS / SS2 SIG FACTORS Refer to sections
3.3.1.2.7
and
3.3.1.2.8
respectively for full
details. The "THRES" entry refers to the Minimum Signal Threshold. The minimum value refers to the
lowest signal strength above zero (0) which allows the antenna controller to confirm that it is pointing to a
satellite rather than pointing to open sky.
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