--- a/src/spectrum/model/friis-spectrum-propagation-loss.cc	Wed Feb 09 16:16:39 2011 +0000
+++ b/src/spectrum/model/friis-spectrum-propagation-loss.cc	Tue Feb 15 12:56:01 2011 +0000
@@ -86,7 +86,8 @@
     }
 
   NS_ASSERT (f > 0);
-  double loss = ( d * f * f) / ((3e8 * 3e8) / (4 * M_PI)) ;
+  double loss_sqrt = (4 * M_PI * f * d) / 3e8;
+  double loss = loss_sqrt * loss_sqrt;
 
   if (loss < 1)
     {

--- a/src/spectrum/model/friis-spectrum-propagation-loss.h	Wed Feb 09 16:16:39 2011 +0000
+++ b/src/spectrum/model/friis-spectrum-propagation-loss.h	Tue Feb 15 12:56:01 2011 +0000
@@ -49,7 +49,7 @@
    * Return the propagation loss L according to a simplified version of Friis'
    * formula in which antenna gains are unitary:
    *
-   *         4 * pi * d * f^2
+   *      (4 * pi * d * f) ^ 2
    * L = ----------------------
    *               C^2
    *