[TowerTalk] Fwd: Fwd: Dbi vs DBd

[hanslg at aol.com]

dBi, (gain over isotropic antenna) refers to something that radiates 
equal in ALL directions. (If you cross two dipoles and feed them 90 
degrees out of phase, you get something very close.) The dipole 
radiates its power in a doughnut shaped pattern with about double the 
field in the maximum direction and (theoretically no field along the 
axle). You may therefor add 3 dB when you "translate" dBd to dBi.

I believe dBi originally was invented to be used in theoretical 
discussions as isotropic radiators usually refers to other types of 
sources such as light and heat (IR) sources and when you calculate 
expected field strengths from radio transmitters.

Hans - N2JFS


-----Original Message-----
From: Michael Ryan <mryan001 at tampabay.rr.com>
Cc: towertalk at contesting.com
Sent: Tue, Nov 3, 2009 4:00 pm
Subject: Re: [TowerTalk] Fwd:  Dbi vs DBd

The terms were and would still be misleading: dbi gain ( gain over
isotropic..what the heck is that? ) and dbd gain over a dipole.  Why 
will
they think of next?...such kidders.  - MIke

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Roger (K8RI)
Sent: Tuesday, November 03, 2009 1:50 PM
To: hanslg at aol.com
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Fwd: Dbi vs DBd

hanslg at aol.com wrote:
> Both were used. Many times a manufacturer used the dBi without 
telling
> as the numbers looked better. To make figures looking even better the
> numbers were also many times "padded".
>
> I, many times, saw figures that just didn't make sense such as a 
dipole
> with some extra coils on stating "8 dB gain". :-)
>
> I would take any information about antenna gain from the 50-s with a
> grain of salt.
>
50's, 60's and 70's, with maybe a few 80's thrown in.<:-))  That was 
why
QST quit advertising gain for antennas. Even in the real, honest world
gain is difficult to get real figures except on a test range and even
then getting the same figures on an average installation is unlikely.

73

Roger (K8RI)
> Hans - N2JFS
>
>
> -----Original Message-----
> From: Andy <ai.egrps at gmail.com>
> To: towertalk at contesting.com
> Sent: Tue, Nov 3, 2009 12:32 pm
> Subject: Re: [TowerTalk] Dbi vs DBd
>
>
>
>> I am trying to find out which of the two measurement references were
>>
> used on
> antennas originating in the late 50's. Say 1959. I know
>
>> in the past one or the other was used, I just dont remember which 
one.
>>
>
> This is just my opinion, mind you ...
>
> But I would guess that both may have been used back then.
>
> Measurement accuracy was not so good in the 1950s that things were
> that precise anyway.
>
> Andy
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