"Ian White GM3SEK" wrote
There isn't really "an" equation for gain versus boom length,
because
boom length is only an indicator of the potentially achievable gain.
But
nothing "makes" a yagi deliver any particular gain figure.

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Ian,

Yes, there must be such an equation. Indeed, there must be a dozen of
them.

I am aware that there are a multitude of things which are, or can be
optimised in the design of Yagis.

I am not interested in how gain can be maximised but what it has
actually turned out to be in practice over the years.

It is a statistical function of the number of elements or of boom
length - which are much the same as each other.

It is just a historical fact which all experienced designers must have
a good idea of but, it seems, are reluctant to divulge.

You probably have a good idea yourself. What is it?

For 2, 3, 4 .... N elements?

Ball park accuracy is too good for it.

I would like to include it in the notes to a practical, general
purpose, computer program which estimates received signal strength
from Tx power and ionospheric radio path distance. It could be titled
"How to use S-meters for Novices". ;o)
----
Reg.