Specifications

5/9/13 888-2857-001 3-29
WARNING: Disconnect primary power prior to servicing.
Section 3 Operation
Platinum VAX-C Series
up to this limit will be linearized by nonlinear RTAC correction. The peak power out of
the exciter must be limited to protect the following amplifier stages.
NOTE:
If this limit is too low, in-band and out-of-band intermodulation products will
increase due to the signal clipping. If the limit is too high, the RTAC nonlinear
corrector performance may be degraded due to high peak stretch. Also high peaks
could cause nuisance overdrive faults in some transmitter systems.
STEP 1 In the ’RTAC’ Setup Screen 1 (on left Figure 3-16 on page 3-24) set
RTAC Linear and Non-Linear functions to ’Bypass’.
STEP 2 The RF output should be set to the level required for transmitter
operation.
STEP 3 In the RTAC ‘Peak Reduction’ sub window of RTAC Setup Screen 3 (on
left Figure 3-17 on page 3-27) verify that the Non-Linear Range and
Max Crest Factor indicators display ‘Enabled’.
STEP 4 In the RTAC ’Peak Reduction’ sub window start with the Non-Linear
Range at the default value. See Table 3-14 on page 27.
STEP 5 With Both RTAC correctors bypassed, the exciter RF output adjacent
channel noise should be 50dB to 55dB below the in band signal level.
As the Nonlinear (Correction) Range value is reduced, the first sign of adjacent channel
intermodulation product increase will be very subtle, with the first sign often being
increased noise in the area just outside the in-band channel bandpass
3.4.3.2 Max Crest Factor Setup
The Max (Maximum) Crest Factor setting limits the peak to average RF output power
ratio (7.8 to 13.0 dB) at the output of the exciter. This directly limits the transmitter RF
output peak to average power ratio. The Crest Factor of the transmitted signal is
determined by this setting and by the peak compression of the amplifier system.
• If the limit is set too low, clipping will generate out-of-band intermodulation
products in the exciter’s output and may affect the performance of the RTAC
non-linear correction.
• If set too high, it could allow nuisance overdrive trips in some transmitter
models, because the high amplitude peaks could overdrive the PA modules.