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Where To Find This Example

AWR Version 14

Understanding AWR .emz Files

AWR Version 13

This example was renamed since the previous version. Please see Previous Example Page for the version 13 page.

Design Notes

Cable TV System Example using Microwave Office 

This example contains a Cable TV (CATV) chain used to analyze the quality of the signals going through the system.   The basic configuration is a CATV signal that gets amplified (usually AGC but modeled as an amplifier), up-converted, filtered, filtered, down-converted, amplified, filtered and amplified.  

           

Overview

The schematic CATV has a chain to be simulated with Harmonic Balance.

The input signal is a 7 channel CATV signal with the center channel starting of 80 dB blow the other channels.  Each of the blocks is a behavioral block.  Each block could be replaced with the physical circuit to be used for the chain.   The project is then displaying the full spectrum at the output of each element.  Equations are used to calculate the difference between the notch channel and the full power channel.  Finally, this channel to notch ratio is plotted versus the stage of the chain.   All of the filters in this example are set to pass all 7 CATV tones to be able to measure the channel to notch ratio. 

Input Signal

The input signal is this example is generated by a PORTMOD_F port.  This port references a signal file located under the Data_Files node called 6toneCATV.   This file specifies relative magnitude and angle of the input spectral components.  If you open this file, you will see the center channel is 80 dB below the other channels.  On the PORTMOD_F element, the center frequency is set by the project or document frequency settings.  The tone spacing is set by the FRES setting, in this case 6 MHz.  The power setting is the total power for all the tones.    Note, in a future version we will have a direct source to create these signals (will eliminate the signal files).   

Harmonic Settings

In this example, the harmonic settings are important to set intelligently to get meaningful and fast simulation results.   The PORTMOD_F take up the first two tone settings.  Tone 1 is the center of this tone grouping, and Tone 2 is for the spacing of the tones.  Tone 1 is set to 1 since this simulation only wants to include one of the input groupings.  Tone 2 is set to 3 to capture all of the tones (only three since the signal file is set to “Double Sided”).  You can try changing the number of Tone 2 settings and watch in the spectrum results.   Tone 3 is the first voltage source on the first mixer.  This is set to 1 to keep the simulation tones down.  If you need to carry multiple harmonics of this mixer frequency, you can change this number.  This was not set higher since the filters would attenuate these higher frequency tones.   Tone 4 is for the voltage source for the 2nd mixer.  For tones higher than 3, the tone settings are controlled on the source themselves, as a secondary parameter.  Again this was set to 1.   For all of the tone settings, you can change their number and watch what happens to the simulation.  

Graphs

This project is plotting the spectrum at the output of each component.  The y-axis has been limited to show a range of 0 to -50dBm.  You may need to change this scale if you want to see more of the higher order tones.

The graph Total Power is plotting the power of the main 7 tones at each stage in the chain.  This was done by using the PTB measurement and specifying the frequency range to measure the power.  You can see the differences between the powers at the different stages match the gain settings for the amplifiers and the mixer. 

Finally the graph, Channel to Notch Power, is plotting how far down the notch channel is compared to the other channels.  This was done using output equations.  For each stage, the notch power and the channel power are returned and the difference is calculated.  These results are put into one vector and then plotted. 

For Further Study

Try changing the specifications on the different parts in the chain to see what happens to the overall system.