Comtech EF Data PCB-4000 - Manual (Page 19)

PCB-4000 1+1 Phase Combiner Revision 2
Introduction MN/PCB4000.IOM
1–5
The amplifier gain difference is automatically compensated for by the PCCB Monitor and Control
System. Upon power up, the M&C reads the gain of each individual amplifier as calibrated at the
factory, and automatically attenuates the amplifier with the most gain so as to be equal with the
lower gain unit.
For example, if SSPA #1 had a factory‐calibrated gain setting of 76 dB, and SSPA #2 had a
factory‐calibrated gain setting of 73 dB, the M&C system would automatically set the
attenuation setting of SSPA#1 to 3 dB to equalize the system gain. Although not generally
needed or recommended, a user input gain offset setting is also provided for system fine‐tuning.
For operation and alignment information, see Chapter 3. INSTALLATION, STARTUP,
AND
TROUBLESHOOTING PROCEDURES.
Note that, due to the power divider and cable losses, the overall gain of the system will be less
than the individual gain of each amplifier. Please refer to the system test data sheet for actual
system gain.
1.3.2 System Attenuation
The PCB‐4000 makes it easy to adjust the overall system gain. Upon input of the requested
attenuation setting, the PCB‐4000 automatically adjusts the gain of each SSPA accordingly,
resulting in the desired attenuation value while maintaining optimum power combining
conditions.
The SSPAs included in the system are calibrated over a range 10 dB beyond specification (30 dB
vs. 20 dB). As explained above, a portion of the 30 dB range is required for gain equalization.
Therefore, the maximum allowable attenuation in a 1+1 system is software limited to 24 dB, but
still exceeds system specifications.
1.3.3 Soft Fail Protection
In the event of a failure of one of the SSPAs, the PCB‐4000 controls the waveguide switches such
that the good unit’s power is routed around the “Magic‐Tee” combiner directly to the output
port. This results in only a 3 dB power loss, or “soft failure”. Without the waveguide switches, a
failure in one unit would result in a 6 dB power loss.