[TowerTalk] Fwd: Dbi vs DBd

[Roger (K8RI)]

Nearly all of my engineering textbooks used dbi, but in the end, it 
makes not a bit of difference whether you use dbi or dbd in the 
practical world *IF* you know which is bing used AND you stick with the 
same units.

db is a *ratio* whether it's db, dbi, or dbd.  Some have a problem when 
the reference is different, but as long as the person reading or doing 
knows the difference it doesn't matter which reference is used.

The dipole reference is often preferred, but the signal from any 
specific dipole is affected by both height and nearby objects. Long haul 
even terrain well outside the "near field" has an effect.  Comparing to 
a dipole in the real world is more or less accurate when both are at the 
same height and location.  Mathematical comparisons are something else 
and there either reference works and is accurate. Note that with a beam 
the front to back and front to side are plain db, rather than dbi or dbd 
as they are referenced back to the strength of the main lobe.

So, for me, I don't care whether they use db, dbi, or dbd as long as I 
KNOW WHICH is bing used. Once you know the shortcuts and rule of thumb, 
db problems become simple enough to work in your head.

73

Roger (K8RI)