wrote:
My ARRL books go back a decade or more
and the graph showing gain per boom length
has several curves based on different measurements
e.t.c. Has a graph been made based solely on NEC
program findings over say a perfect ground and at a uniform height?

There is a table of data calculated by VE7BQH for a large number of
different yagis, at:
http://www.ifwtech.co.uk/g3sek/diy-yagi/ve7bqh.htm
(These are not calculated by NEC, but by another very adequate program.)

You can draw your own curve from the data in the L(WL) and Gain columns.
Since all the data have been calculated by the same person, starting
from the antenna's mechanical dimensions, and using the same program,
this removes a lot of variables.

You will see a broad trend of increasing gain with boom length, but
there is still a lot of scatter due to variations between different
designs. Also bear in mind that gain isn't everything, and a long yagi
that has been maximized for gain may be a poor antenna in other ways,
such as sidelobe levels, ease of pointing, sensitivity to water on the
elements, ease of matching etc.

Drawing gain curves is a fun activity... but don't try to read too much
into them.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek