If an external modulation source is selected, 
modulation depth is determined by a ± 5V signal input 
into the MOD INPUT terminal on the rear panel. For 
example, if the modulation depth is set to 100%, then 
when the voltage level of the modulation source is at 
+5V, then the deviation is at the maximum and when 
the source is at -5V then the deviation is at the 
minimum.