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N6156A & W6156A DTMB (CTTB) Digital Video X-Series Measurement Application

Technical Overviews

Introduction 

This demonstration guide illustrates how the DTMB (CTTB) measurement application adds convenience to DTMB (CTTB) system development and manufacturing for both multi-carrier and single carrier schemes with one-button measurements including standard presets and remote SCPI programming capabilities on the X-Series signal analyzers. 

DTMB (CTTB) Digital Video Measurement Details 

All of the RF transmitter measurements as defined by the DTMB (CTTB) standard, as well as a wide range of additional measurements and analysis tools, are available with a press of a button (Table 2). These measurements are fully remote controllable via the IEC/IEEE bus or LAN, using SCPI commands. Analog baseband measurements are available on the MXA signal analyzer equipped with BBIQ hardware. Supported baseband measurements include all of the modulation quality plus I/Q waveform and CCDF measurements. 

Demonstration Preparation Minimum equipment configuration requirements 

All demonstrations use an X-Series signal analyzer and the N5182A MXG vector signal generator. 

Demonstration Setup Connect the PC, X-Series, and MXG 

Connect a PC (loaded with Keysight N7623B Signal Studio for Digital Video software and Keysight I/O libraries) to the N5182A MXG via GPIB or LAN. Follow the Signal Studio instruction to complete the connection, and then perform the following steps to interconnect the X-Series signal analyzer and MXG (see Figure 1 for a graphical overview): A. Connect the MXG RF output port to the X-Series signal analyzer RF input port B. Connect the MXG 10 MHz out to the X-Series signal analyzer Ext Ref in port (rear panel) 

Set up Digital Video Signal Studio on MXG 

The Keysight N7623B Signal Studio for Digital Video is a Windows-based utility that simplifies the creation of DTMB (CTTB) signals. These signal parameters are downloaded into the MXG vector signal generator, which creates the desired waveform. 

Channel power 

The channel power measurement has three views: RF spectrum, shoulder attenuation, and spectrum mask. The RF spectrum view measures and reports the integrated power in a DTMB (CTTB) defined bandwidth and power spectral density (PSD) displayed in dBm/Hz or dBm/MHz. The shoulder attenuation view measures the power difference between the center frequency (CF) and the shoulder point (4.2 MHz from CF for 8 MHz bandwidth). The spectrum mask view compares the input signal against the DTMB (CTTB) defined spectrum mask for the condition of analog TV signal in adjacent channel. 

Spectrum mask view 

The dynamic range of the RF output of a real DTMB (CTTB) transmitter typically exceeds the dynamic range of the analyzer. Therefore, the direct measurement result is always “FAIL” and cannot reflect the real RF output. To measure the spectrum mask of the transmitter’s RF output, there are two methods. Method 1 When the DTMB (CTTB) transmitter has an output filter, the diagram for the spectrum mask measurement is shown in Figure 5. Three steps for measuring the spectrum mask are as follows: A. Measure the frequency response of the output filter using a network analyzer or a combination of signal source and signal analyzer. B. Measure the signal transmitted at point A as shown in Figure 5. C. Apply amplitude correction on spectrum value measured in (2) using the filter’s response from (1). The correction data is typically a table of the filter’s frequency response in dB, at a number of frequency points across the band. Method 2 When the transmitter does not have an output filter, an external filter with a band-block filter frequency response should be added after the transmitter for the measurement arrangement shown in Figure 6. The steps for measuring the spectrum mask are as follows: A. Measure the frequency response of the output filter using a network analyzer or a combination of signal source and signal analyzer. B. Measure the signal transmitted at point B as shown in Figure 6. C. Apply amplitude correction on spectrum value measured in (2) using the filter’s response from (1). The correction data is typically a table of the filter’s frequency response in dB, at a number of frequency points across the band. The correction data is typically a table of the negative values of this bandblock filter’s frequency response in dB, at a number of frequency points across the band. This spectrum mask measurement is used in case there are analog TV signals in the adjacent channel. Note: In spectrum mask view, if the device type is exciter or the bandwidth is 6 MHz, the mask trace will not be displayed and a “No Result” message will be displayed because the spectrum masks for those cases are not defined in the DTMB (CTTB) specifications. 

Adjacent channel power (ACP) 

ACP is a measurement of the power in adjacent in-band or out-band channels relative to the transmitted power. The ACP test verifies the ability of the modulator or transmitter to limit the interference produced by the transmitted signal to other receivers operating at the adjacent in-band or adjacent out-band RF channel. The ACP measurement results should look like Figure 9. The text window shows the power inside adjacent channel and outside adjacent channel as the standard requires. 

Power stat CCDF) 

The power stat CCDF (complementary cumulative distortion function) is a statistical method used to interpret the peak-to-average ratio of digitally modulated noise-like signals. It is a key tool for the power amplifier design in DTMB (CTTB) transmitters, which is particularly challenging because the amplifier must be capable of handling the high peak-to-average ratio while maintaining good adjacent channel leakage performance. 

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