diff --git a/nanovna.h b/nanovna.h
index 5827db7..18fd053 100644
--- a/nanovna.h
+++ b/nanovna.h
@@ -168,7 +168,7 @@ extern char *hw_text;
 #define HIGH_MAX_FREQ_MHZ   1130
 #define MINIMUM_DIRECT_FREQ  823000000ULL
 #define ULTRA_AUTO         10000000000ULL // 10GHz
-
+#define MAX_CTCSS_FREQ  255
 
 //#define LOW_MAX_FREQ         800000000ULL
 //#define MIN_BELOW_LO         550000000ULL   // not used????
diff --git a/sa_core.c b/sa_core.c
index 7280a66..85013ab 100644
--- a/sa_core.c
+++ b/sa_core.c
@@ -3542,9 +3542,9 @@ static const int fm_modulation[MODULATION_TABLES][MAX_MODULATION_STEPS] =
 #ifdef TINYSA3
 static const int fm_modulation_offset[4] =
 {
-   85000,
+   83125,   // 80000 + 2*LND*156.25  (LND=10, low band step = 156.25 Hz)
    80000,
-  165000,
+  163750,   // 160000 + 2*HND*312.5  (HND=6,  high band step = 312.5 Hz)
   160000
 };
 #endif
@@ -3752,9 +3752,12 @@ pureRSSI_t perform(bool break_on_operation, int i, freq_t f, int tracking)     /
           modulation_steps >>= 1;
         }
         if (modulation_steps >= 4) {
-          int hn = (config.wfm_1khz_harmonic > 0 && setting.modulation_frequency < 250.0) ? (int)((1000.0 / setting.modulation_frequency) + 0.5) : 0;
+          int hn = (config.wfm_1khz_harmonic > 0 && setting.modulation_frequency < MAX_CTCSS_FREQ) ? (int)((1000.0 / setting.modulation_frequency) + 0.5) : 0;
+          int local_deviation = setting.modulation_deviation_div100;
+          if (hn)
+            local_deviation /= 7;                   // 15% CTCSS deviation
           for (int i = 0; i < modulation_steps/4+1; i++) {
-            fm_modulation[i] = setting.modulation_deviation_div100 * sine_wave[i*sine_wave_index]/100;
+            fm_modulation[i] = local_deviation * sine_wave[i*sine_wave_index]/100;
             fm_modulation[modulation_steps/2 - i] = fm_modulation[i];
             fm_modulation[modulation_steps/2 + i] = -fm_modulation[i];
             fm_modulation[modulation_steps - i] = -fm_modulation[i];
diff --git a/ui.c b/ui.c
index 46e9e61..ee25796 100644
--- a/ui.c
+++ b/ui.c
@@ -2512,9 +2512,11 @@ static UI_FUNCTION_ADV_CALLBACK(menu_audible_harmonic)
   (void)item;
   (void)data;
   if (b){
-    b->icon = config.wfm_1khz_harmonic ? BUTTON_ICON_CHECK : BUTTON_ICON_NOCHECK;
+    b->icon = (config.wfm_1khz_harmonic && setting.modulation_frequency < MAX_CTCSS_FREQ) ? BUTTON_ICON_CHECK : BUTTON_ICON_NOCHECK;
     return;
   }
+  if (setting.modulation_frequency >= MAX_CTCSS_FREQ)
+    return;
   config.wfm_1khz_harmonic = config.wfm_1khz_harmonic ? 0 : 100;  // Toggle between off and 100%
   dirty = true;
 //  menu_move_back(false);
@@ -4472,7 +4474,7 @@ static const menuitem_t  menu_modulation[] = {
   { MT_FORM | MT_KEYPAD,   KM_MODULATION,           "FREQ: %s",         "1Hz..3.5kHz"},
   { MT_FORM | MT_KEYPAD,   KM_DEPTH,               "AM DEPTH: %s%%",         "0..100"},
   { MT_FORM | MT_KEYPAD,   KM_DEVIATION,            "FM DEVIATION: %s",         "1kHz..300kHz"},
-  { MT_FORM | MT_ADV_CALLBACK, 0,                   "Add Audible harmonic", menu_audible_harmonic},
+  { MT_FORM | MT_ADV_CALLBACK, 0,                   "CTCSS + 1 kHz", menu_audible_harmonic},
 //  { MT_FORM | MT_ADV_CALLBACK, MO_NFM2,              MT_CUSTOM_LABEL,    menu_modulation_acb},
 //  { MT_FORM | MT_ADV_CALLBACK, MO_NFM3,              MT_CUSTOM_LABEL,    menu_modulation_acb},
 #else