diff --git a/SP5WWP/m17-coder/Makefile b/SP5WWP/m17-coder/Makefile
index ca184c9..1293125 100644
--- a/SP5WWP/m17-coder/Makefile
+++ b/SP5WWP/m17-coder/Makefile
@@ -1,5 +1,5 @@
-m17-coder-sym: m17-coder-sym.c golay.c
-	gcc -O2 -w -lm m17-coder-sym.c golay.c -o m17-coder-sym
+m17-coder-sym: m17-coder-sym.c golay.c crc.c
+	gcc -O2 -w -lm m17-coder-sym.c golay.c crc.c -o m17-coder-sym
 
 clean:
 	rm m17-coder-sym
diff --git a/SP5WWP/m17-coder/crc.c b/SP5WWP/m17-coder/crc.c
new file mode 100644
index 0000000..200cd87
--- /dev/null
+++ b/SP5WWP/m17-coder/crc.c
@@ -0,0 +1,23 @@
+#include <string.h>
+#include <stdint.h>
+#include "crc.h"
+
+const uint16_t M17_CRC_POLY = 0x5935;
+
+uint16_t CRC_M17(const uint8_t *in, const uint16_t len)
+{
+	uint32_t crc=0xFFFF; //init val
+
+	for(uint16_t i=0; i<len; i++)
+	{
+		crc^=in[i]<<8;
+		for(uint8_t j=0; j<8; j++)
+		{
+			crc<<=1;
+			if(crc&0x10000)
+				crc=(crc^M17_CRC_POLY)&0xFFFF;
+		}
+	}
+
+	return crc&(0xFFFF);
+}
diff --git a/SP5WWP/m17-coder/crc.h b/SP5WWP/m17-coder/crc.h
new file mode 100644
index 0000000..1b7ee2e
--- /dev/null
+++ b/SP5WWP/m17-coder/crc.h
@@ -0,0 +1,6 @@
+#ifndef CRC_H
+#define CRC_H
+
+uint16_t CRC_M17(const uint8_t *in, const uint16_t len);
+
+#endif
diff --git a/SP5WWP/m17-coder/m17-coder-sym.c b/SP5WWP/m17-coder/m17-coder-sym.c
index 476d9cf..dee2fa6 100644
--- a/SP5WWP/m17-coder/m17-coder-sym.c
+++ b/SP5WWP/m17-coder/m17-coder-sym.c
@@ -5,6 +5,7 @@
 
 #include "../inc/m17.h"
 #include "golay.h"
+#include "crc.h"
 
 struct LSF
 {
@@ -92,8 +93,6 @@ void conv_Encode_Frame(uint8_t* out, uint8_t* in, uint16_t fn)
 	//encode
 	for(uint8_t i=0; i<144+4; i++)
 	{
-		//uint8_t G1=(ud[i+0]                +ud[i+3]+ud[i+4])%2;
-		//uint8_t G2=(ud[i+0]+ud[i+1]+ud[i+2]        +ud[i+4])%2;
 		uint8_t G1=(ud[i+4]                +ud[i+1]+ud[i+0])%2;
         uint8_t G2=(ud[i+4]+ud[i+3]+ud[i+2]        +ud[i+0])%2;
 
@@ -117,6 +116,18 @@ void conv_Encode_Frame(uint8_t* out, uint8_t* in, uint16_t fn)
 	//printf("pb=%d\n", pb);
 }
 
+uint16_t LSF_CRC(struct LSF *in)
+{
+    uint8_t d[28];
+
+    memcpy(&d[0], in->dst, 6);
+    memcpy(&d[6], in->src, 6);
+    memcpy(&d[12], in->type, 2);
+    memcpy(&d[14], in->meta, 14);
+
+    return CRC_M17(d, 28);
+}
+
 //main routine
 int main(void)
 {
@@ -278,6 +289,11 @@ int main(void)
             while(read(STDIN_FILENO, &(lsf.meta), 14)<14);
             while(read(STDIN_FILENO, data, 16)<16);
 
+            //calculate LSF CRC
+            uint16_t ccrc=LSF_CRC(&lsf);
+            lsf.crc[0]=ccrc>>8;
+            lsf.crc[1]=ccrc&0xFF;
+
             got_lsf=1;
 
             //send out the preamble and LSF