______________________________________________
HARRIS
888-9058-001
WARNING: Disconnect and lockout AC primary power prior to servicing
28
average power levels while maintaining out of band emission specifications by filtering
IMD product near the mask filter shoulder. Some RF systems contain channel combiners,
allowing two or more channels to share the same transmission line and antenna.
Directional coupler units develop RF samples for metering RF power levels and are used as
feedback samples for the exciter real time correction circuits. The IPA sample inputs on the
Apex exciter are not used, therefore the Apex exciter IPA mode should be set to bypass.
The Platinum transmitter system interconnect drawings detail these RF sample connections.
The combining of transmitters on different frequencies often require special attention to
the sample lines for exciter correction and VSWR monitoring. The sample lines may
require filtering and phasing networks to remove unwanted frequencies in the RF samples.
This is critical for RTAC samples.
1.4 Platinum RF Combining Parameters
1.4.1.01 Two PA Cabinets
The parameters for the two cabinet system are easy to determine by applying the hybrid
rules for division and combining to determine how to calibrate the cabinet power levels
and the reject load wattage. When one cabinet does not put out power, the other cabinet
will deliver half of its output power to the antenna, the other half to the reject load. The
cabinet output power is calibrated in watts and the reject power in percentage of the
loads rating.
Example:
Total power out (TPO) is 7.4 KW, each cabinets output is 3.7 KW (ignoring losses) and
cabinet half power would be 1.85 KW. The reject load is rated at 2.5 KW, the power
calibration in this case would be 1.85 / 2.5 or 74 percent.
1.4.0.2 Percent of Cabinet Power With Three PA Cabinets
CABINET
CABINET
CABINET
A/B
AB/C COMBINED
A
B
C
REJECT REJECT OUTPUT
100
0
0
50 16.6 33.3
0
100
0
50 16.6 33.3
0
0
100
0 66.6 33.3
100
100
0 0 66.6 133.3
100
0
100 50 16.6 133.3
100
100
100 0 0 300