Harris ATLAS ANALOGUE, Manual

Page: 131 / 134

7/26/05 888-2523-001 4-17
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
ATLAS Analogue
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 characterized and the results used to generate a lookup table to set the
thresholds for the fault comparators.
The comparator fault thresholds are set using "EEPOTS". These are basically
programmable electronic potentiometers that are being programmed by the micro
module based on the lookup table mentioned above.
Example: (Note: The following values are used for example only)
At a reference frequency of 600MHz, 100mW of RF input = 3Vdc detected output
At a transmitter frequency of 500MHz, 100mW of RF input = 3.4Vdc detected output
When the GUI is configured for a transmitter frequency of 500MHz, the micro module
on the RF Monitor board receives this information. The micro module would then look
up the 500MHz frequency in the table and set the fault threshold of the comparator
(using the EEPOT) for 3.4Vdc instead of the 3Vdc used at the reference frequency.
The comparator is now calibrated to trip when 1000W is applied to the reject load being
monitored without having to re-calibrate the detector.
4.4.3.2.2 PA Module Phase Alignment
The outputs of the reject load detectors are also multiplexed into a 10bit ADC (Analog
to Digital Converter) on the micro module. The ADC output will be between 0 and
1023 for a given input voltage range of 0 - 4Vdc. This ADC number shows up on the
"PA Reject Service" screen on the GUI. For a detailed PA Module and Cabinet phasing
procedure refer to "5.4 PA Module Phasing" on page 5-6.