@Red:
It works for me:
http://www.candyparty.com/ST/BMS_433/picture/coms_TWR_1.png
and if I change the BUP manual frequency to 306.8, then my Ded shows UHF ON / BACKUP, 6, 306.8
You are not in Manual.
You report using MAN but there is no MAN option. There is a MAIN option on the left knob. That may be your problem
For MaNuaL frequency to be active you must use the right knob out of PRESET to MNL
Dash-1 p24
As you said, “That may be your problem.” Exactly, that was my problem. Along with your new Spotlight and your insightful advice, I can see clearly now that the label on the Backup UHF panel is Main, not Man. Now it works for me, too. I’ll join the BMS Falcon pilots from the whole world to say thanks for ALL of the monumental results you produced for all of us.