[App_rpt-users] How do I setup channel B to generate a PL tone?

I am using the RPi2-3 image on a Pi3 and the RB-USB-RIM. I would like to set Channel B to output a PL tone of 110.9 Hz. In SimpleUSB, I have set txmixb=tone. I have set the level to 500. Using an oscilloscope, I see no output from Channel B. Where do I set the frequency and how do I enable it? Tnx Steve N8AR