3.5DB splitter loss in voltage?
The power ratio is the square of the voltage "ratio". 

The power ratio is 10^-.35 or .44 - ie, just under half the power to each output with the total output power less than the input due to some loss (and/or approximation in the 3.5 dB number)

Taking the square root for the voltage ratio halves the exponent,

ie 10^-.175 or .668 of the input voltage.  Comparatively, for a lossless ideal splitter, you would expect SQRT(.5) or .707 of the input voltage on each output port.

There's an assumption that all ports connect to systems of the intended characteristic impedance; if not, the numbers will be skewed.