spaß mit frequenzmodulation

frequenzmodulation.m

@@ -0,0 +1,57 @@
+
+#d = [ 1 0 1 0 1 0 0 1 0 1 1 ];
+datalen = 30;
+d = rand(1,datalen) < 0.5;
+n = 0:datalen-1;
+Tb = 0.2;
+fa = 2000;
+freq = [ 50 30 ];
+signallen = (datalen*Tb-1/fa)
+t = 0:(1/fa):signallen;
+f = freq(d(floor(t/Tb)+1)+1);
+phi = cumsum(2*pi*f)/fa;
+s = cos(phi);
+
+subplot(4,1,1)
+stem(n,d)
+subplot(4,1,2)
+plot(t,s)
+axis([0 signallen -1 1])
+
+[b,a] = butter(5,2*mean(freq)/fa);
+
+slow = filter(b,a,s);
+st = abs(slow);
+
+[b2,a2] = butter(10,2*(min(freq)*0.8)/fa);
+hk = filter(b2,a2,st);
+
+subplot(4,1,3)
+cla; hold on;
+plot(t,slow,'k')
+plot(t,st,'g')
+plot(t,hk,'r')
+hold off
+axis([0 signallen -1 1])
+
+mt = zeros(size(n));
+for i = 1:datalen
+  ts = (i-1) * Tb;
+  te = i * Tb;
+  tf = t > ts & t < te;
+  mt(i) = mean(hk(tf));
+endfor
+hold on;
+stem((n+0.5)*Tb,mt,'r');
+hold off;
+
+thr = (min(mt) + max(mt)) / 2;
+
+ds = mt > thr;
+
+subplot(4,1,4)
+err = ds != d;
+cla; hold on;
+stem(n(~err),ds(~err))
+stem(n(err),ds(err),'rx')
+hold off;