12/20/11 888-2595-001 4-3
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
ZX Series
For example, a ZX5000 with one of eight PA modules removed produces (7/8) or
87.5% (4375W) of the original power with (7/8)^2 or 76.6% (3830W) appearing at the
transmitter output and the remainder 10.9% (545W) being dissipated in the ballast
loads.
Applying this formula to the various transmitter models yields the following power
outputs when a single PA module is removed:
ZX2500 = -2.5 dB (56.3%)
ZX3750 = -1.6 dB (69.4%)
ZX5000 = -1.2 dB (76.6%)
The same rule also applies to combining perfomed outside the PA chassis in an external
combiner, yielding the following results for higher power models:
ZX7.5 = -0.8 dB (84.0%)
ZX10 = -0.6 dB (87.9%)
Because both halves of the IPA operate in parallel in all models, the resulting power at
the PA chassis output from the loss of one IPA half is always (1/2)^2 = -6dB (25%).
Note that the IPA is operated at reduced power and is not exposed to the vagaries of the
output transmission line and antenna. Therefore, it can be expected to have a very low
risk of failure.
The loss of a single IPA results in the following power outputs for the various
transmitter models:
ZX2500 / ZX3750 / ZX5000 = -6dB (25%)
ZX7.5 / ZX10 = -2.5 dB (56.3%)
The loss figures given here should be considered a worst-case scenario. The regulating
action of the transmitter automatic power control (APC) will attempt to raise the power
output to compensate for the drop. How much loss will be compensated depends on the
transmitter power level, the APC setup procedure used, and how close the transmitter is
to saturation (FM mode).
Even when all PA modules are installed in the transmitter and operating, power could
be wasted in the ballast loads if all modules are not fully balanced in amplitude and
phase. For this reason, it is imperative to always use the correct part number PA
modules in the transmitter. Do not mix different part number PA modules in the same
transmitter, as these may not have the same phase and gain characteristics.
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