diff --git a/CHANGELOG b/CHANGELOG
index da3669e..1a0aad0 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,8 @@
 SIGNAL SERVER CHANGELOG 
 
+2.63 - 10 Nov 2015
+Added sanity check and handicap to ECC33 model when used with low Tx heights in hilly areas = sea of red
+
 2.62 - 30 Oct 2015
 Fixed near field 'lattice' bug at 30m resolution caused by previous fix to fill in void around antenna.
 Credit to Nils Lofstad for helping nail this down.
diff --git a/main.cc b/main.cc
index 2de8ad5..26069e5 100644
--- a/main.cc
+++ b/main.cc
@@ -1,4 +1,4 @@
-double version = 2.62;
+double version = 2.63;
 /****************************************************************************\
 *       Signal Server: Server optimised SPLAT! by Alex Farrant               *
 ******************************************************************************
diff --git a/models/ecc33.cc b/models/ecc33.cc
index d4c5f23..642234f 100644
--- a/models/ecc33.cc
+++ b/models/ecc33.cc
@@ -5,6 +5,11 @@
 double ECC33pathLoss(float f, float TxH, float RxH, float d, int mode)
 {
 
+	// Sanity check as this model operates within limited Txh/Rxh bounds
+	if(TxH-RxH<0){
+		RxH=RxH/(d*2);
+	}
+
 	if (f < 700 || f > 3500) {
 		printf("Error: ECC33 model frequency range 700-3500MHz\n");
 		exit(EXIT_FAILURE);
@@ -22,5 +27,6 @@ double ECC33pathLoss(float f, float TxH, float RxH, float d, int mode)
 	if (mode > 1) {		// Medium city (Europe)
 		Gr = (42.57 + 13.7 * log10(f)) * (log10(RxH) - 0.585);
 	}
+
 	return Afs + Abm - Gb - Gr;
 }
diff --git a/models/los.cc b/models/los.cc
index 64d9c1b..0264654 100644
--- a/models/los.cc
+++ b/models/los.cc
@@ -338,7 +338,7 @@ void PlotPropPath(struct site source, struct site destination,
 
 			char fd_buffer[64];
 			int buffer_offset = 0;
-	    
+
 			distance = 5280.0 * path.distance[y];
 			xmtr_alt =
 			    four_thirds_earth + source.alt + path.elevation[0];
diff --git a/models/sui.cc b/models/sui.cc
index 3d2b3c2..db0eaf5 100644
--- a/models/sui.cc
+++ b/models/sui.cc
@@ -41,9 +41,9 @@ double SUIpathLoss(float f, float TxH, float RxH, float d, int mode)
 	}
 	double d0 = 100;
 	double A = 20 * log10((4 * M_PI * d0) / (300 / f));
-	double y = (a - b * TxH) + c / TxH;
+	double y = a - (b * TxH) + (c / TxH);
 	double Xf = 6 * log10(f / 2000);
-	double Xh = XhCF * log10(RxH / 2);
+	double Xh = XhCF * log10(RxH / 20);
 
-	return A + (10 * y * log10(d / d0)) + Xf + Xh + s;
+	return A + (10 * y) * (log10(d / d0)) + Xf + Xh + s;
 }