dansawyeror wrote:
There are three terms, idb, pdb, and vdb. They are not the same. idb
and pdb have the same value: 10*log10 (i/i0), while vdb is
20*log10(v/v0).


"A decibel is a decibel is a decibel". There is only one kind of
decibel, and by definition it is based on a power ratio.

Decibels are always used for comparing power levels. If you're comparing
current or voltage levels, you first have to convert them into a power
ratio, and that is the reason why you have to use a different formula.
Your starting-point was different, but the definition of the decibel
remains the same.


There is a similar-looking term, sometimes written as either "dBV",
"dBmV" or "dBuV", but that has a different meaning. Anything tagged on
after the "dB" indicates a standard reference level. For example, "dBV"
means "a power ratio in decibels, relative to the power level of a 1V
rms signal measured at the same point in the circuit."


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek