UBS Axcera HU5000AD, LU3000BTD, DT325B, CU150BTD, LHV60ATD Users Manual

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

DTVision Eye Screen

I-Signal Eye Display

Graphic display of the eight data amplitude levels. This can be used to monitor the demodulated 8VSB signal. When signal is precise, the seven vertical "eyes" will appear (this display shows two sets). Linear or non-linear distortion in the modulator process will cause incorrect I-signal amplitude at center of "eye" pattern. Transmitter distortion such as group delay, frequency tilt, or ripple will cause the "eye" to close and result in receiver data errors.

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

Linear Equalizer Graph

Linear Equalizer Display:

This display shows the characteristics of the linear adaptive equalizer. The horizontal axis is frequency (0 to 5.38 MHz). There are two traces on this display. One shows the amplitude of the

equalizer's response in decibels, and the other shows the group delay of the equalizer in nanoseconds. The vertical scale for the amplitude display is along the left side of the display. The range is always –3 to +3 decibels. The group delay scale automatically scales itself to the equalizer data, and the minimum and maximum values appear along the right side of the scale.

Since this display shows the equalizer characteristics, the channel (transmitter) characteristics, which are being corrected, will be the inverse of the equalizer. For example, if the equalizer shows a rising amplitude response with increasing frequency, then the transmitter has a falling amplitude response with increasing frequency. The same inverse relationship also holds with respect to group delay.

In normal operation, the amplitude response will be generally flat, and the group delay curve will drop off at the frequency extremes (near 0 and 5.38 MHz) because of the channel filter's group delay.

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

Linear Quad Display Screen

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

DTVision Non-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 Nonlinear screens have the following reference values displayed

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

ever negative, then there is clipping in the IF modulator, nonlinear equalizer, and/or the DAC. If this happens, lower the unity gain reference point for the nonlinear equalizer.

EVM

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).

Digital to Analog Converter (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 occurring in the IF modulator, nonlinear equalizer, and/or the DAC. If this happens, lower the unity gain reference point for the nonlinear equalizer.

Peak to Average Ratio

This value shows the peak to average ratio of the transmitted signal. This value is typically 6 to 8 dB for a perfect signal. A value significantly lower will indicate peak compression. A small amount of peak compression is normal.

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

DTVision Non-Linear Home/Spectrum Screen

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

DTVision Peak to Average Screen

Peak to Average Ratio Display:

This screen shows the peak to average ratio in a statistical fashion. The red trace shows the ideal signal's peak to average ratio statistics, and the yellow trace shows the statistics of the transmitter's output.

The curves show the cumulative distribution function of the peak to average ratio's probability density.

The horizontal scale shows the peak to average ratio measured in decibels. The vertical scale shows the percentage of the time that the peak to average ratio exceeds the value on the horizontal scale. The vertical scale is logarithmic.

When the transmitter is clipping signal peaks, the low probability, high peak to average portion of the (yellow) curve for the transmitter's output will appear to the right of the (red) curve indicating the ideal signal.

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

Nonlinear Phase Amplitude Display

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

Nonlinear Equalizer Display

Nonlinear Equalizer Display:

This display shows the nonlinear corrections being applied to the signal to correct for the RF power amplifier’s envelope compression and incidental phase modulation. The horizontal axis is the ideal RF envelope magnitude. The yellow magnitude trace shows the instantaneous gain correction being applied to the signal as a function of the desired envelope amplitude, to correct for amplitude compression in the power amplifier. The red phase trace shows the amount of phase correction being applied to correct for the power amplifier’s incidental phase modulation.

As the ideal amplitude becomes large (corresponding to the right part of the display), the probability density function of the ideal envelope magnitude becomes very small or zero. So, data in the right hand portion of the display will generally be extrapolated. Also, the magnitude equalization characteristic may also drop off, to accomplish clipping and to prevent overflow of the data feeding the DAC.

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

Nonlinear Quad Display Screen

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

Upconverter Screen

This screen shows controls and status values related to the upconverter.

Channel Select:

Entering a number in this box selects the channel. Channels 2-6 are VHF low band, 7-13 are VHF high band, and channels 14-69 are UHF. (If the channel number is ever changed, the channel filter in the upconverter will need to be replaced or retuned to the new channel.)

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Digital ATSC Exciter-Modulator System Chapter 2, Installation and Operating Instructions

LO Frequency DWNC Output Gain AGC Manual AGC Target Power Level AGC 1 Gain Value AGC 1 Voltage AGC 2 Gain Value AGC 2 Voltage UPC RF Output Level Overdrive Threshold External Mute UPC Pin Attenuation Level UPC 1GHz LO Level Variable LO AFC Variable LO PLL 10MHz Reference UPC Serial Bridge

This value indicates whether or not the Serial Bridge between the Netburner and the Micro ATX computer is up and operational.

Axciter On Air

This value indicates if this Axciter is On Air. This value is received from the UP/DWN converter.

UPC IF Input Overdrive Status UPC Fault Status

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