The Distortion Analyser, Thd , and Sinad Lab Report

Table of Contents Page Number

1.0 Theory............................................................................................1

1.1 The Distortion Analyzer, THD, and SINAD.....................................2

1.2 AM Receiver Design..................................................................2

2.0 Lab Objectives.................................................................................2

3.0 Procedure.......................................................................................3

3.1 Distortion Analyzer, THD, and SINAD Procedure ...........................3

3.2 AM Receiver Design and Test Procedure......................................4

4.0 Calculations.....................................................................................6

4.1 Distortion Analyzer, THD, and SINAD Calculations.........................6

4.2 AM Receiver Calculations........................................................10

5.0 Equations......................................................................................12

6.0 Conclusion....................................................................................14

7.0 Equipment List...............................................................................15

List of Figures, Graphs, Tables Page Number

Figure 6.1: AM Receiver Design..............................................................11

Graph 6.1: Measured/Predicted SNR(dB) Versus

US Attenuation for 0dB Attenuated DS Signal..............................................8

Graph 6.2: Measured/Predicted SNR(dB) Versus

US Attenuation for 6dB Attenuated DS Signal..............................................9

Graph 6.3: Measured/Predicted SNR(dB) Versus US Attenuation for 12dB Attenuated DS Signal............................................................................10

Table 6.1: Signal Powers and Frequencies .................................................6

Table 6.2: Signal Sideband Power Results...................................................6

Table 6.3: Reference Power Results..........................................................6

Table 6.4: Measured and Predicted SNR(dB) for 0dB Attenuated DS Signal......7

Table 6.5: Measured and Predicted SNR(dB) for 6dB Attenuated DS Signal......8

Table 6.6: Measured and Predicted SNR(dB) for 12dB Attenuated DS Signal.....9

Table 6.7: AM Receiver Design Results....................................................10

Table 6.8: Signal Powers and Frequencies................................................11

Table 6.9: Overall and Amplifier Noise Figures...........................................12

Table 6.10: Devices Used......................................................................15

1.0 Theory

1.1 The Distortion Analyser, THD, and SINAD

A distortion analyzer is an instrument that allows measurement of desired signal power and noise power of an audio signal that has both noise and a desired signal. The total harmonic distortion is defined as the ratio of RMS noise to RMS signal and noise. The total harmonic distortion is calculated in dB using Equation 6.1 below:

Equation 6.1:

Another term called the SINAD is defined as the ratio of signal power plus noise to the noise power. The SINAD in dB is equal to the negative THD in dB. The SINAD as a ratio is equal to the signal to noise ratio plus one. Equation 6.2 can be used to calculate the SNR if the SINAD in decibels is known:

Equation 6.2:

1.2 AM Receiver Design

Many of the theories used for designing an AM receiver are developed in previous lab reports. The most important consideration when designing an AM receiver is the signal to noise ratio. The sideband power present at the receiver input must be greater than the effective noise power at the input by the acceptable signal to noise ratio. The total input power to the detector must also be large enough to turn the diode on during valleys of modulation. This means the minimum voltage values during demodulation need to be larger than the turn on voltage for the diode to prevent distortion. The gain from antenna to detector must amplify the minimum required receive power to the minimum required detector power. A design that achieves this specification should successfully demodulate a received AM signal.

2.0 Lab Objectives

This lab report covers two experiments: the distortion analyzer and AM receiver design. The lab objectives for the distortion analyzer experiment are to understand how the distortion analyzer measured the total harmonic distortion, understand how to interpret the distortion analyzers measurement, to understand the relationship between total harmonic distortion and SINAD, and to calculate the signal to noise ratio using the SINAD.

The lab objectives for the AM receiver design experiment are to use the theories and concepts from previous labs and lectures to design a working AM receiver on paper, to build the design, to determine the overall noise figure for the AM receiver system, and to determine the noise figure for each amplifier used in the design.

3.0 Procedure

3.1 Distortion Analyzer, THD, and SINAD Procedure

Step 1: Determine Frequency and Power at Signal Ports

Measure the power level and frequency of the DS and US channels. A modulation index of 60% is to be assumed for the DS signal,