Update operating-instructions.md

amunters · Dec 19, 2017 · 76c6d84 · 76c6d84
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diff --git a/operating-instructions.md b/operating-instructions.md
@@ -19,6 +19,8 @@ Depending on the user's choice, additional functionality provided by this softwa
 - remove R101 (disable the original analog crystal BFO oscillator)
 - install a short shielded cable between the Raduino si5351 CLK0 output and pin 6 of T4 on the BitX40 main board
 
+As the BFO signal is now generated by the si5351, the received audio may initially sound unnatural (pitched too low or too high). Perform the calibration procedures to precisely calibrate the VFO and BFO frequency.
+
 ![image of digital BFO mod](digital%20BFO%20mod.png)
 
 ## CLARIFIER