B-Netz: Improved detection of tone/frame

- Be less tollerant to levels when detcting tones.
- Squelch applies to tone detector also

docs/b-netz.html

@@ -531,6 +531,12 @@ Then tune to actually up-link frequency 148.410 MHz.
 The actual level is not yet relevant.
 </p>
 
+<p>
+<font color="red">Hint: Use squelch on the receiver, to prevent noise from beeing detected as signaling information!</font>
+<br><br>
+If you use SDR, use the squelch option.
+</p>
+
 <pre>
 
 # src/bnetz/bnetz -k 1