Harris Atlas DVL1100, Техническое руководство

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4-28 888-2473-001 2/25/03
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation ATLAS Series™
4.4.6.2 Reject Load RF Detector (Relative)
The reject load RF detectors are a diode based envelope detector. These detectors
are intended to provide relative readings only, not accurate absolute power
measurements. The inputs for these detectors come from the 40dB attenuators being
used as reject loads for the PA module combiner. Each detector has 3 dynamically
adjustable gain settings, Low, Medium and High. The chosen sample levels from
the reject loads and the gain of the detectors allow them to operate in the Low gain
position for normal operation.
In other words, for a 500W reject load (which is actually a 40dB attenuator) with
500W applied, the RF input sample to the detector would be 50mW. In the Low
gain position, this would give approximately 3Vdc detected output (the actual
output voltage is dependent on frequency). This 3Vdc level (adjusted for frequency)
is used to protect the reject loads from over-dissipation.
The Medium and High gain settings are only used when adjusting module or cabinet
phasing to minimise combiner reject load power. When you leave the "Phase Align"
screen on the GUI all detectors default back to the Low gain setting.
The reject load RF detector samples are used for 2 purposes:
•
Overload protection of the reject loads
•
PA Module and Cabinet RF phase alignment
4.4.6.2.1 Reject Load Protection
The reject load detector outputs are sent to comparators for detection of overloads
which could potentially damage the load. There are 2 sizes of reject loads possible;
500W and 1000W (depending on transmitter model). If these loads were dissipating
their maximum power levels then their sample outputs to the detectors would be
40dB less or 50mW and 100mW respectively. The detectors are calibrated (by a
fixed voltage divider on the RF Monitor board) to produce a 3Vdc output at this
maximum RF input level.
If the detector output reaches 3Vdc the fault comparators will trip, causing a
FAULT_OFF to be sent over the parallel control bus, shutting the transmitter off.
The micro module will communicate the cause of the fault to the Main Controller
over the CAN bus.
The detectors do not have perfect frequency response over the entire UHF band.
Therefore, to eliminate calibration requirements, the detector Output Voltage vs.
Frequency was characterised and the results used to generate a lookup table to set
the thresholds for the fault comparators.