Decibels Engineers often measure the ratio of two power measurements in decibels

Question

Decibels Engineers often measure the ratio of two power measurements in decibels, or dB. The equation for the ratio of two power measurements in decibels is dB = 10 log_10 P_2/P_1 where P_2 is the power level being measured, and P_1 is some reference power level. (a) Assume that the reference power level P_1 is I milliwatt, and write a program that accepts an input power P_2 and converts it into dB with respect to the 1 mW reference level. (Engineers have a special unit for dB power levels with respect to a 1 mW reference: dBm.) Use good programming practices in your program. (b) Write a program that creates a plot of power in watts versus power in dBm with respect to a 1 mW reference level. Create both a linear y plot and a log-linear plot.

Explanation / Answer

1) Matlab code:

clc; clear all;close all;
p2 = input('Enter P2 in milliWatts');
p1 = 1;
dB = 10*log10(p2/p1);
fprintf('dB power level = %d', dB);

2)

Linear Plot Matlab code:

clc; clear all;close all;
x1 = input('Enter P2 in milliWatts first reading');
p1 = 1;
dB1 = 10*log10(x1/p1);

x2 = input('Enter P2 in milliWatts second reading');
dB2 = 10*log10(x2/p1);

x = [x1,x2];
y = [dB1, dB2 ];

plot(x,y,'o');
axis([0 (max(x) + 10) 0 max(y) + 10]);
xlabel('power in milliwatt')
ylabel('dB');

Log-linear plot Matlab code:

clc; clear all;close all;
x1 = input('Enter P2 in milliWatts first reading');
p1 = 1;
dB1 = 10*log10(x1/p1);

x2 = input('Enter P2 in milliWatts second reading');
dB2 = 10*log10(x2/p1);

x = [x1,x2];
y = [dB1, dB2 ];

plot(log10(x),y,'o');
axis([0 (max(log10(x)) + 10) 0 max(y) + 10]);
xlabel('Log(power in milliwatt)')
ylabel('dB');

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