With Spectran setup selected to the preset NDB mode (0 to 7400 Hz.) As soon as I press the start button, a red vertical line appears in the upper spectrum display at 3500 Hz. What is it and is there any way to turn it of? Thanks in advance for any replies. 73, J.B., VE3EAR LowFER Beacon "EAR" 188.830 kHz. QRSS30 EN93dr