Richard, the more I study the boom length question the more I feel that the
ARRL
should drop the three curve gain/boom length graph. First there has to be a
condition that all elements are on the same plane. The other condition must
be
that all the elements are straight and parallel. The more I study the two
element
antenna I find that changing the added element height relative to one
another ,
even if a small distance , can change the gain.
I understand that there are "Landorfer ?"curved elements that can also
increase the gain.
I also proved that by NEC.
If one allows elements numbers to be added to increase ad hoc then NEC shows
that a quasi dish shape will occur
where the focus can stay equal to .1 wavelength and where gain increases to
over 14 dbi.
If one takes a further step by "shaping "the elements whether it be the feed
element or the
reflective elements then not only does the beam width narrow with increased
gain but the
TAO decreases about one degree which is a huge advantage when using small
garden type antennas.
Based on the above findings it would be impossible to generate a NEC curve
that would make sense
unless the above two conditions are set in place for the average amateur.
The latter would give
some protection against fraudulent vendors and supply a datum curve that is
meaningful to all.
I do believe that this posting should put an end to this thread and I thank
you again for your input.
Regards
Art



"Richard Harrison" wrote in message
...
Art Unwin wrote:
"My ARRL books go back a decade or more and the graphs showing the gain
per boom length has several curves based on different measurements
e.t.c."

I haven`t encountered similar curves based on NEC, but I`ve found thye
old ARRL curves on page 163 of my 1970 edition of the "A.R.R.L. Antenna
Book" (cover price=$2.50).

Variation between curves from 3 different groups of observers are within
"1 S-unit" (6 dB). Gain ranges from a minimum of about 7 dB for a Yagi
with a 1/2-wave boom length (pessimistic) to a 19 dB gain for a
6.5-wavelength boom length (optimistic).

The optimistic curve is labeled "Greenblum", and seems too good to be
true. The other two curves have flattened out as the number of
wavelengths increases. The Greenblum curve is almost a straight line. As
Kraus showed in his solution to the Deutsche Welle antenna gain problem,
you often need to double the total number of elements to get a 3 dB
antenna gain.

Best regards, Richard Harrison, KB5WZI