User's Manual

Digital ATSC Exciter-Modulator System Chapter 2,
Installation and Operating Instructions
Axcera Axciter, Rev. 0 25
DTVision Linear - Optional
This section contains information regarding the DTVision Screens. These screens are
optional diagnostic screens. They are not necessary for the operation of the Axciter.
However, they greatly enhance the experience. These graphs provide the same type of
views as an EFA.
All of the Linear Screens have the following reference values on the bottom of the screens.
dB Stretch
This value is the maximum amount of gain boost being generated by the
Nonlinear Equalizer. This value is approximately equal to the maximum
amount of gain compression of the power amplifier.
dB Compression
This value is the minimum amount of gain being generated by the Nonlinear
Equalizer. This value is indicative of any relative "stretch" being produced in
the power amplifier.
Phase Shift
This is the maximum value of instantaneous phase shift being produced by the
Nonlinear Equalizer. This value corresponds to the incidental phase
modulation of the power amplifier.
dB Boost
This is the maximum amount of amplitude boost being produced by the Linear
Equalizer. This value corresponds to the lowest point in the channel frequency
response.
dB Attenuation
This is the minimum gain level being produced by the Linear Equalizer. This
value corresponds to the highest point in the channel frequency response.
ns Equalizer Delay
This is the maximum group delay variation in nanoseconds of the Linear
Equalizer.
EVM
The error vector magnitude (EVM) value indicates quality of the digital
modulation. EVM is defined as the RMS error at the sampling instants divided
by the RMS of the ideal symbols. The error is expressed as a percentage. As
signal quality increases, this value decreases.
S/N
The transmitted signal quality is also expressed as an in-band signal to noise
ratio, expressed in dB. As signal quality increases, this value will increase
(logarithmically).
DAC Headroom
This parameter shows the amplitude (in dB) of the equalized IF signal with
respect to the maximum output from the digital to analog converter (DAC). A
positive value indicates normal operation and no clipping. If this value is ever
negative, then there is clipping in the IF modulator, nonlinear equalizer,