graphics_toolkit gnuplot N = 500; %length of plot sams = 0:N; cycles = 0.25; % 1/4 cycle of phi(t) cyc_per_sam = cycles/N; phi = pi/2 * sin(2*pi*cyc_per_sam*sams); cycles = 4; % 4 cycles of carrier wave cyc_per_sam = cycles/N; z = cos(2*pi*cyc_per_sam*sams + phi); %carrier x = cos(2*pi*cyc_per_sam*sams).*cos(phi); %in-phase y = cos(2*pi*cyc_per_sam*sams + pi/2).*sin(phi); %quadrature figure plot(sams,sin(phi),'color','red', 'linewidth', 3) %envelope ylim([-1.2 1.2]); box off hold on plot(sams,cos(phi),'color','blue', 'linewidth', 3) %envelope plot(sams,x,'color','blue') plot(sams,y,'color','red') plot(sams,z,'color','green', 'linewidth', 2) set(gca, 'xaxislocation', 'origin') set(gca, 'yaxislocation', 'origin') set(gca, 'xgrid', 'on'); set(gca, 'ygrid', 'off'); set(gca, 'ytick', [0]); cycles_per_tick = 0.25; sam_per_tick = cycles_per_tick/cyc_per_sam; set(gca, 'xtick', [0:16]*sam_per_tick); set(gca,'XTickLabel',[' 0'; ' '; '2'; ' '; '4'; ' '; '6'; ' '; '8'; ' '; ' '; '11'; ' '; '13'; ' '; '15'; ' ']) green = [0 170 0]/256; text(400, .9, '\uparrow sin(\phi(t))', 'color', 'red') text(30, .86, '\uparrow cos(\phi(t))', 'color', 'blue') text(147, .44, '\leftarrow I(t)', 'color', 'blue') text(165, .30, 'Q(t) \rightarrow', 'color', 'red') text(121, 1, '\leftarrow cos(2\pift + \phi(t)) \rightarrow', 'color', green) text(146, .87, '= I(t)+Q(t)', 'color', green) title('In-phase and quadrature components (example)','fontsize', 12); xlabel('\leftarrow time (t) \rightarrow','fontsize', 12) ylabel('amplitude','fontsize', 10)