# Decibel question

#### joka2188

Joined Nov 10, 2006
9
If there is a voltage signal loss of - 6 dB along a cable, giving a 2V output, determine the input voltage.
Basically, i know how to find the voltage signal loss which is VdB = 20log (vout/Vin), (if anyone thinks this is incorrect would you let me know). So basically how would you maniuplate this formula so you can find out Vin if you're only give Vout and VdB.

#### Papabravo

Joined Feb 24, 2006
14,847
Proceed as follows
Rich (BB code):
VdB = 20 * log (Vout / Vin)        (divide both sides by 20
VdB/20 = log(Vout / Vin)           (exponentiate both sides
10^(VdB/20) = Vout / Vin           (multiply both sides by Vin
Vin * (10^(VdB/20)) = Vout         (divide both sides by 10^...
Vin = Vout / (10^(VdB/20))