Add implementation of analog TV signal generator (PAL so far)

Quick and dirty Howto:
make && tv/osmotv --sdr-soapy --sdr-tx-gain 60  -r 15000000 -c 21 tx-fubk --sdr-tune-args "OFFSET=-3000000"

src/tv/tv_modulate.c

@@ -0,0 +1,35 @@
+/* television modulator
+ *
+ * (C) 2017 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <math.h>
+#include <stdint.h>
+#include "../common/sample.h"
+#include "tv_modulate.h"
+
+#define WHITE_MODULATION	0.1
+
+void tv_modulate(float *buff, int count, sample_t *bas, double amplitude)
+{
+	int i, ss = 0;
+
+	for (i = 0; i < count; i++) {
+		buff[ss++] = ((1.0 - bas[i]) * (1.0 - WHITE_MODULATION) + WHITE_MODULATION) * amplitude;
+		buff[ss++] = 0;
+	}
+}