User's Manual

PINEAPPLE TECHNOLOGY, INC V.6 - ADAPTIVE PRE-CORRECTOR WEB SERVICE OPERATION
DXDPRO-10VH MODULATOR MANUAL
THE INFORMATION PROVIDED HEREIN IS PINEAPPLE TECHNOLOGY INCORPORATED PROPRIETARY INFORMATION AND
CANNOT BE COPIED OR DISTRIBUTED WITHOUT PRIOR AUTHORIZATION
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V.6 ADAPTIVE PRE-CORRECTOR WEB SERVICE OPERATION (Continued)
E. APPENDIX-A CLIPPER OPERATION
1. GENERAL INFORMATION
The clipper function included with the PT2000 Terrestrail Gateway unit allows a controlled limitation of
the output signals peak-to-average-power-ratio (PAPR).
When the clipper is disabled the output from the PT2000 Terrestrail Gateway unit will exhibit a PAPR
equivalent to the inherent PAPR for the modulation format when the unit is configured/operated as a
modulator. When the unit is configured as repeater or transposer the PAPR of the processed signal may
be limited by headroom constraints in equipment prior to the repeater or transposer input. In the latter
scenario the PAPR measured on the RF output may therefore be lower than the inherent PAPR for the
modulation format in question even when the clipper is off.
Although the highest power peaks for multicarrier COFDM formats like DVB-T and MediaFLO reach a
level about 15dB over the signals average RMS power the high peaks have limited energy content. The
peaks are therefore not of immediate danger to the safe operation of a power amplifier following the
modulator output even in the normal case where the average power setting for the amplifier is not
backed off with the full PAPR relative to the peak power rating for the amplifier. The highest peaks are
simply clipped by the power amplifier. However, a performance improvement and an extension of
amplifier lifetime may be obtained if the peaks are limited to a point just below the amplifiers clip point by
the clipper function of the PT2000 Terrestrail Gateway unit. When the clipping is done the following
characteristics are obtained:
a) The potential short time effect on the amplifier characteristic after a power peak is eliminated; the
clipping in the Terrestrial Gateway is an instant process with no subsequent effect on the signal
processing characteristic.
b) The unavoidable noise that results from the clipping, when the clipping takes place in the PT2000
Terrestrial Gateway unit, may be distributed as preferred by use of the ‗soft clipper‘ function (see
below). When the clipping occurs in the amplifier the noise resulting from the clipping will be
distributed evenly below, within and above the used channel. When using the clipper function of the
Terrestrial Gateway the noise may be displaced from the upper and lower sideband of the channel
to minimize disturbance of adjacent channels.
c) By clipping the signal in the PT2000 Terrestrail Gateway unit any possible degradation of amplifier
life time by repeated peak power stress is minimized.
2. OPERATION OF THE CLIPPER FUNCTION
Level Definition
The point of clipping relative to average power level for the signal processed can be set by dragging the
clipper block to the configuration panel. The Clipper level control can be set in the range from 12dB to
2dB. This setting refers to the baseband processing which is equivalent to a range from 15dB to 5dB for
the actual RF output (the addition to the signal of a single CW carrier, the local oscillator used in the up-
conversion process, corresponds to an increase of the PAPR by 3dB).