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Re: [TowerTalk] Fwd: Dbi vs DBd

To: "'Roger \(K8RI\)'" <K8RI-on-TowerTalk@tm.net>, "'Tower Talk'" <towertalk@contesting.com>
Subject: Re: [TowerTalk] Fwd: Dbi vs DBd
From: "AD5VJ Bob" <rtnmi@sbcglobal.net>
Date: Tue, 3 Nov 2009 20:44:54 -0600
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
What about antenna design applications, do they give you a choice or one or the 
other as a standard?

Bob AD5VJ 

> -----Original Message-----
> From: towertalk-bounces@contesting.com 
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Roger (K8RI)
> Sent: Tuesday, November 03, 2009 7:36 PM
> To: Tower Talk
> Subject: Re: [TowerTalk] Fwd: Dbi vs DBd
> 
> 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)
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