diff --git a/CMakeLists.txt b/CMakeLists.txt
index d0a2816..9b79036 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -88,6 +88,13 @@ if (DCR)
     add_definitions(-DJPNDCR_DECODE)
 endif ()
 
+#use cmake option -DNOS=ON to enable older NXDN sync w/ pos and inv polarity, disable newer seperated (disabled by default)
+option(NOS
+    "Build with Old NXDN Sync (pos and inv polarity) Enabled" OFF)
+if (NOS)
+    add_definitions(-DNXDN_OLD_SYNC)
+endif ()
+
 #use cmake option -DSID=ON to enable P25p1 Soft ID decoding -- Experimental
 option(SID
     "Build with P25p1 LSD/Soft ID Enabled" OFF)
diff --git a/src/dsd_frame_sync.c b/src/dsd_frame_sync.c
index efc19b5..9d29836 100644
--- a/src/dsd_frame_sync.c
+++ b/src/dsd_frame_sync.c
@@ -1140,55 +1140,56 @@ getFrameSync (dsd_opts * opts, dsd_state * state)
                  }
 
             }
+          #ifdef NXDN_OLD_SYNC
+          //NXDN (previous sync, now a cmake option -DNOS=ON ..)
+          else if ((opts->frame_nxdn96 == 1) || (opts->frame_nxdn48 == 1))
+          {
+            strncpy (synctest10, (synctest_p - 9), 10); //FSW only
+            if (
+                   (strcmp (synctest10, "3131331131") == 0 ) //this seems to be the most common 'correct' pattern on Type-C
+                || (strcmp (synctest10, "3331331131") == 0 ) //this one hits on new sync but gives a bad lich code
+                || (strcmp (synctest10, "3131331111") == 0 )
+                || (strcmp (synctest10, "3331331111") == 0 )
+                || (strcmp (synctest10, "3131311131") == 0 ) //First few FSW on NXDN48 Type-C seems to hit this for some reason
 
-          // //NXDN (previous sync, revert if issues / complaints arise)
-          // else if ((opts->frame_nxdn96 == 1) || (opts->frame_nxdn48 == 1))
-          // {
-          //   strncpy (synctest10, (synctest_p - 9), 10); //FSW only
-          //   if (
-          //          (strcmp (synctest10, "3131331131") == 0 ) //this seems to be the most common 'correct' pattern on Type-C
-          //       || (strcmp (synctest10, "3331331131") == 0 ) //this one hits on new sync but gives a bad lich code
-          //       || (strcmp (synctest10, "3131331111") == 0 )
-          //       || (strcmp (synctest10, "3331331111") == 0 )
-          //       || (strcmp (synctest10, "3131311131") == 0 ) //First few FSW on NXDN48 Type-C seems to hit this for some reason
+                )
+            {
 
-          //       )
-          //   {
+              if (state->lastsynctype == 28)
+              {
+                state->offset = synctest_pos;
+                state->max = ((state->max) + lmax) / 2;
+                state->min = ((state->min) + lmin) / 2;
+                state->last_cc_sync_time = time(NULL);
+                return (28);
+              }
+              state->lastsynctype = 28;
+            }
 
-          //     if (state->lastsynctype == 28)
-          //     {
-          //       state->offset = synctest_pos;
-          //       state->max = ((state->max) + lmax) / 2;
-          //       state->min = ((state->min) + lmin) / 2;
-          //       state->last_cc_sync_time = time(NULL);
-          //       return (28);
-          //     }
-          //     state->lastsynctype = 28;
-          //   }
+            else if (
 
-          //   else if (
+                       (strcmp (synctest10, "1313113313") == 0 )
+                    || (strcmp (synctest10, "1113113313") == 0 )
+                    || (strcmp (synctest10, "1313113333") == 0 )
+                    || (strcmp (synctest10, "1113113333") == 0 )
+                    || (strcmp (synctest10, "1313133313") == 0 )
 
-          //              (strcmp (synctest10, "1313113313") == 0 )
-          //           || (strcmp (synctest10, "1113113313") == 0 )
-          //           || (strcmp (synctest10, "1313113333") == 0 )
-          //           || (strcmp (synctest10, "1113113333") == 0 )
-          //           || (strcmp (synctest10, "1313133313") == 0 )
+                    )
+            {
 
-          //           )
-          //   {
-
-          //     if (state->lastsynctype == 29)
-          //     {
-          //       state->offset = synctest_pos;
-          //       state->max = ((state->max) + lmax) / 2;
-          //       state->min = ((state->min) + lmin) / 2;
-          //       state->last_cc_sync_time = time(NULL);
-          //       return (29);
-          //     }
-          //     state->lastsynctype = 29;
-          //   }
-          // }
+              if (state->lastsynctype == 29)
+              {
+                state->offset = synctest_pos;
+                state->max = ((state->max) + lmax) / 2;
+                state->min = ((state->min) + lmin) / 2;
+                state->last_cc_sync_time = time(NULL);
+                return (29);
+              }
+              state->lastsynctype = 29;
+            }
+          }
 
+          #else //new sync
           //NXDN (positive sync only)
           else if (opts->inverted_nxdn == 0 && ((opts->frame_nxdn96 == 1) || (opts->frame_nxdn48 == 1)) )
           {
@@ -1242,6 +1243,7 @@ getFrameSync (dsd_opts * opts, dsd_state * state)
             }
 
           }
+          #endif
 
           //Provoice Conventional -- Some False Positives due to shortened frame sync pattern, so use squelch if possible
           #ifdef PVCONVENTIONAL
diff --git a/src/dsd_main.c b/src/dsd_main.c
index c16bc02..7ffc2d4 100644
--- a/src/dsd_main.c
+++ b/src/dsd_main.c
@@ -1490,7 +1490,11 @@
    printf ("  -xx           Expect non-inverted X2-TDMA signal\n");
    printf ("  -xr           Expect inverted DMR signal\n");
    printf ("  -xd           Expect inverted ICOM dPMR signal\n");
+   #ifdef NXDN_OLD_SYNC
+   //
+   #else
    printf ("  -xn           Expect inverted NXDN/DCR/IDAS signal\n");
+   #endif
    printf ("\n");
    printf ("  * denotes frame types that cannot be auto-detected.\n");
    printf ("  ** Phase 2 Single Frequency may require user to manually set WACN/SYSID/CC parameters if MAC_SIGNAL not present.\n");
@@ -2759,7 +2763,11 @@
              sprintf (opts.output_name, "NXDN48");
              fprintf (stderr,"Setting symbol rate to 2400 / second\n");
              fprintf (stderr,"Decoding only NXDN 4800 baud frames.\n");
+             #ifdef NXDN_OLD_SYNC
+             //
+             #else
              fprintf(stderr, "Notice: NXDN autodetect polarity disabled. \n Use -xn option if Inverted Signal expected.\n");
+             #endif
            }
            else if (optarg[0] == 'y')
            {
@@ -3084,7 +3092,11 @@
            else if (optarg[0] == 'n')
            {
              opts.inverted_nxdn = 1;
+             #ifdef NXDN_OLD_SYNC
+             //
+             #else
              fprintf (stderr, "Expecting inverted NXDN/DCR/IDAS signals.\n");
+             #endif
            }
            break;