Hello all, this is a formula that calculates DDM (depth of modulation) at certain outputs of the ILS's Glideslope. I posted this question some time ago but I think I left out some important details. Any help is really appreciated. This is basic info on the ILS http://en.wikipedia.org/wiki/Instrument_Landing_System db = 20log(E1/E2) E1 is the input voltage before attenuation E2 is the output voltage after attenuation E1 and db seems like is always given. E2 is what needs to be solved. My course book rearranges the formula to this: E2 = E1log-1(db/20) -that makes NO sense to me. Log to negative power - or the reciprical? this is one of the examples they have: db = -3 E1 = .155 E2 = .155log-1(-3/20) = 0.109 more examples: 2.5log-1(-3/20) = 1.77 1.0log-1(-3/20) = 0.707 .494log-1(-3/20) = 0.342 Is there another way to rearrange the formula that makes sense? Thank you.