diff --git a/htdocs/lib/MapMarkers.js b/htdocs/lib/MapMarkers.js
index 4b839228..877f8e88 100644
--- a/htdocs/lib/MapMarkers.js
+++ b/htdocs/lib/MapMarkers.js
@@ -292,11 +292,7 @@ FeatureMarker.prototype.getInfoHTML = function(name, receiverMarker = null) {
         for (var j=0 ; j<this.schedule.length ; ++j) {
             var freq = this.schedule[j].freq;
             var mode = this.schedule[j].mode;
-            var tune = mode === 'cw'?      freq - 800
-                     : mode === 'fax'?     freq - 1900
-                     : mode === 'rtty450'? freq - 1000
-                     : mode === 'sitorb'?  freq - 1000
-                     : freq;
+            var tune = Utils.offsetFreq(freq, mode);
 
             var name = ('0000' + this.schedule[j].time1).slice(-4)
                 + '&#8209;' + ('0000' + this.schedule[j].time2).slice(-4)
diff --git a/htdocs/lib/Utils.js b/htdocs/lib/Utils.js
index 89c6faf0..68de83dd 100644
--- a/htdocs/lib/Utils.js
+++ b/htdocs/lib/Utils.js
@@ -22,6 +22,26 @@ Utils.htmlEscape = function(input) {
     return $('<div/>').text(input).html()
 };
 
+// Change frequency as required by given modulation
+Utils.offsetFreq = function(freq, mod) {
+    switch(mod) {
+        case 'cw':
+            return freq - 800;
+        case 'fax':
+            return freq - 1900;
+        case 'cwdecoder':
+        case 'rtty450':
+        case 'rtty170':
+        case 'rtty85':
+        case 'sitorb':
+        case 'bpsk31':
+        case 'bpsk63':
+            return freq - 1000;
+    }
+
+    return freq;
+}
+
 // Wrap given callsign or other ID into a clickable link.
 Utils.linkify = function(id, url = null, content = null, tip = null) {
     // If no specific content, use the ID itself