diff --git a/doc/user_guide/en/odds_and_ends.adoc b/doc/user_guide/en/odds_and_ends.adoc
index be71faa19..f83690314 100644
--- a/doc/user_guide/en/odds_and_ends.adoc
+++ b/doc/user_guide/en/odds_and_ends.adoc
@@ -36,3 +36,12 @@ End of line information::
  `T` - Length of analyzed region (s)
 
 === Reference Spectrum
+
+WSJT-X provides a tool that can be used to determine the detailed
+shape of your receiver's passband.  Disconnect your antenna or tune to
+a quiet frequency with no signals.  With WSJT-X running in one of the
+slow modes, select *Measure reference spectrum* from the *File menu.
+Wait for about a minute and then hit the *Stop* button.  A file named
+`refspec.dat` should appear in your log directory.  
+
+[ ... more to come ...]