Richard Harrison wrote:
My original comment was in support of Arnold B. Bailey who said
something about increasing antenna gain by 3 dB every time you double
its size. Precisely, that`s not true, but I gave an example from Kraus
where he did much the same thing.

+3dB is a valid generalization, based on sound physics - but it is only
a generalization.

At the time those Grand Old Men were writing their textbooks, such
generalizations were the best that anybody could manage. But they had no
way of checking their accuracy - or more important, why and when they
start to become INaccurate.

50 years on, we do have a way, and we now know much more than they did.
That makes it very dangerous to quote those Grand Old Generalizations as
accurate and universal truths. Richard was quite correct to describe the
"+3dB rule" as "naive" - because, at today's level of knowledge, it is.

But we still need to know that the +3dB generalization exists; and
understand the fundamental reasons for it. That fundamental
understanding is what protects us against stupid mistakes.


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