diff --git a/main.c b/main.c
index 2a292d4..88b429a 100644
--- a/main.c
+++ b/main.c
@@ -494,6 +494,9 @@ freq_mode_centerspan(void)
 }
 
 
+#define START_MIN 500000
+#define STOP_MAX 300000000
+
 void
 set_sweep_frequency(int type, int frequency)
 {
@@ -501,6 +504,8 @@ set_sweep_frequency(int type, int frequency)
   case ST_START:
     ensure_edit_config();
     freq_mode_startstop();
+    if (frequency < START_MIN)
+      frequency = START_MIN;
     if (freq_start != frequency) {
       freq_start = frequency;
       update_frequencies();
@@ -509,6 +514,8 @@ set_sweep_frequency(int type, int frequency)
   case ST_STOP:
     ensure_edit_config();
     freq_mode_startstop();
+    if (frequency > STOP_MAX)
+      frequency = STOP_MAX;
     if (freq_stop != frequency) {
       freq_stop = frequency;
       update_frequencies();
@@ -519,6 +526,16 @@ set_sweep_frequency(int type, int frequency)
     freq_mode_centerspan();
     if (freq_start != frequency) {
       freq_start = frequency;
+      int center = freq_start;
+      int span = -freq_stop;
+      if (center-span/2 < START_MIN) {
+        span = (center - START_MIN) * 2;
+        freq_stop = -span;
+      }
+      if (center+span/2 > STOP_MAX) {
+        span = (STOP_MAX - center) * 2;
+        freq_stop = -span;
+      }
       update_frequencies();
     }
     break;
@@ -527,6 +544,25 @@ set_sweep_frequency(int type, int frequency)
     freq_mode_centerspan();
     if (freq_stop != -frequency) {
       freq_stop = -frequency;
+      int center = freq_start;
+      int span = -freq_stop;
+      if (center-span/2 < START_MIN) {
+        center = START_MIN + span/2;
+        freq_start = center;
+      }
+      if (center+span/2 > STOP_MAX) {
+        center = STOP_MAX - span/2;
+        freq_start = center;
+      }
+      update_frequencies();
+    }
+    break;
+  case ST_CW:
+    ensure_edit_config();
+    freq_mode_centerspan();
+    if (freq_start != frequency || freq_stop != 0) {
+      freq_start = frequency;
+      freq_stop = 0;
       update_frequencies();
     }
     break;
@@ -559,6 +595,10 @@ static void cmd_sweep(BaseSequentialStream *chp, int argc, char *argv[])
       int32_t value = atoi(argv[1]);
       set_sweep_frequency(ST_SPAN, value);
       return;
+    } else if (strcmp(argv[0], "cw") == 0) {
+      int32_t value = atoi(argv[1]);
+      set_sweep_frequency(ST_CW, value);
+      return;
     }
   }
 
diff --git a/nanovna.h b/nanovna.h
index 809cec7..5c4aa56 100644
--- a/nanovna.h
+++ b/nanovna.h
@@ -197,7 +197,7 @@ void cal_collect(int type);
 void cal_done(void);
 
 enum {
-  ST_START, ST_STOP, ST_CENTER, ST_SPAN
+  ST_START, ST_STOP, ST_CENTER, ST_SPAN, ST_CW
 };
 
 void set_sweep_frequency(int type, int frequency);
diff --git a/plot.c b/plot.c
index 1636cfb..e027f7f 100644
--- a/plot.c
+++ b/plot.c
@@ -1251,7 +1251,7 @@ draw_frequencies(void)
                (int)((fstop / 1000) % 1000),
                (int)(fstop % 1000));
     ili9341_drawstring_5x7(buf, 205, 233, 0xffff, 0x0000);
-  } else {
+  } else if (fstop < 0) {
     int fcenter = fstart;
     int fspan = -fstop;
     chsnprintf(buf, 24, "CENTER %d.%03d %03d MHz  ",
@@ -1264,6 +1264,15 @@ draw_frequencies(void)
                (int)((fspan / 1000) % 1000),
                (int)(fspan % 1000));
     ili9341_drawstring_5x7(buf, 205, 233, 0xffff, 0x0000);
+  } else {
+    int fcenter = fstart;
+    chsnprintf(buf, 24, "CW %d.%03d %03d MHz    ",
+               (int)(fcenter / 1000000),
+               (int)((fcenter / 1000) % 1000),
+               (int)(fcenter % 1000));
+    ili9341_drawstring_5x7(buf, OFFSETX, 233, 0xffff, 0x0000);
+    chsnprintf(buf, 24, "                             ");
+    ili9341_drawstring_5x7(buf, 205, 233, 0xffff, 0x0000);
   }
 }
 
diff --git a/ui.c b/ui.c
index 8c6f918..741f8cd 100644
--- a/ui.c
+++ b/ui.c
@@ -60,7 +60,7 @@ enum {
 };
 
 enum {
-  KM_START, KM_STOP, KM_CENTER, KM_SPAN, KM_SCALE
+  KM_START, KM_STOP, KM_CENTER, KM_SPAN, KM_CW, KM_SCALE
 };
 
 uint8_t ui_mode = UI_NORMAL;
@@ -305,6 +305,7 @@ menu_stimulus_cb(int item)
   case 1:
   case 2:
   case 3:
+  case 4:
     ui_mode_keypad(item);
     ui_process_keypad();
     break;
@@ -410,6 +411,7 @@ const menuitem_t menu_stimulus[] = {
   { MT_CALLBACK, "STOP", menu_stimulus_cb },
   { MT_CALLBACK, "CENTER", menu_stimulus_cb },
   { MT_CALLBACK, "SPAN", menu_stimulus_cb },
+  { MT_CALLBACK, "CW", menu_stimulus_cb },
   { MT_CANCEL, "BACK", NULL },
   { MT_NONE, NULL, NULL } // sentinel
 };
@@ -805,6 +807,9 @@ ui_process_keypad(void)
   case KM_SPAN:
     set_sweep_frequency(ST_SPAN, value);
     break;
+  case KM_CW:
+    set_sweep_frequency(ST_CW, value);
+    break;
   case KM_SCALE:
     set_trace_scale(uistat.current_trace, value);
     break;