As an addendum to Bill's e-mail here is are a couple of snippets that many
people don't think about much. "In the Trade" it used to be usual to
advertise antenna gain in dBd for frequencies below 1GHz- and dBi for
Often these days advertisers use dBi regardless of the frequency 'cos to the
uninitiated it looks like 2.15 dB higher gain for your money. I think dBi
should be the de facto standard for all antenna gain figures, even though
the concept is a little harder to grasp.
The second and more important point is that the advertised gain figure for a
particular antenna may be correct, but the maximum gain is not necessarily
where the design would lead you to believe it is.
For example I have measured an omnidirectional VHF antenna that claimed to
be 6 dBd gain -and it was- but at an angle of 12 degrees above the horizon.
the result being that the gain where you want it -on the horizon -was less
than 5 dBd.
The better manufacturers will publish both vertical slice plots and
horizontal slice plots for their antennas, but even this may not tell you
the whole story, because there are so many different scales used for the
plots. Something that should be standardized world wide through the ITU.
72 de G8BOU/VE3CHH
Subject: [GQRP] Careless dBd-ing
>From: "L. B. Cebik" <firstname.lastname@example.org>
>Some comparisons referenced on one of the distribution lists gave me the
occasion to do a short note on Some Pitfalls of Careless dBd-ing
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