Modulation Menu
When no span for sweeping is selected the output can be modulated according to a limited set of formats.
- NONE sets no modulation
 - AM sets an AM modulation.
 - FM sets FM modulation.
 - FREQ activates a keypad to set the modulation frequency between 50Hz and 6kHz.
 - AM DEPTH activates a keypad to set the AM modulation depth between 10% and 100%
 - FM DEVIATION activates a keypad to set the FM deviation between 1kHz and 300kHz
 - BACK will move back to the previous menu