Index: trunk/BNC/bnchelp.html
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--- trunk/BNC/bnchelp.html	(revision 1283)
+++ trunk/BNC/bnchelp.html	(revision 1285)
@@ -642,4 +642,7 @@
 </ul>
 <p>
+Note that in RTCM Version 2.x the message types 18 and 19 carry only the observables of one frequence. Hence it needs two type 18 and 19 messages to transport the observations from dual frequency receivers.
+</p>
+<p>
 
 <p>Logged time stamps refer to message reception time and allow to understand repetition rates. Enter 'ALL' if you want to log this information from all configured streams. Beware that the size of the logfile can rapidly increase depending on the number of incoming RTCM streams.