"Ian White, G3SEK" wrote in message
...
Richard wrote:
3 When you use a metallic boom, you have to make corrections to the
element lengths as per Table 10.

That's Figure 10. Those corrections will only apply if you use the same
method as they did for mounting an element on a round metal boom...
which they don't specify in detail, so Fig 10 is almost worthless.

That's why Iasked the question could I could appreciate this issue.

4 I take it that whatever you put in place for DE, all spacing and
reflector and director elements continue to remain correct. So you can
place
whatever you want for DE, hertz dipole, folded dipole, gamma match, T
match, DE with 1/"4 dia tube or 1.2" dia tube -it does not matter,
parasitic element lengths once calculated need not be changed whatever
you
DE you place in the design. Spacing always remain the same.

It does in the NBS designs; but not in most more modern designs.

5 How do you go about designing for DE?

Too big a subject - look it up teh basic principles and some practical
examples in various antenna handbooks, and then go and get your hands
dirty.

Whenever anyone produces a design for a yagi, who has built a practical
model, whether a test model like NBS did, or whether a model built by Joe
Ham, then the DE is already designed. Most people who want to build a yagi
don't want to design from scratch, they just want to be presented with a
design methodology that's simple, that allows for some slight variation in
materials or method of fixing.

So the design methodologies that appeal a

Copying exactly someone else's design.(No design involved)

Trying to design with Technical Note 688. (Looked promising at first).

Taking someone's design and adjusting for variation in element diameter and
boom size using some program or other. (This involves ELE.EXE I think).

Taking a model and designing with that with a program. But I've got the
impression, rightly or wrongly, that going this route is getting away from
the concept of "simple design methodology". I think that stems from my
inability to have noted these programs allowing boom parameters to be
inputed, and I'm totally in the dark about DE in these programs.

All the really simple methodologies have as starting point a practical
proven design. All one is doing is making certain kinds of alterations:
frequency, boom size, element diameters, and if you really want to
adventurous, alter element fixing method, but that could be an alteration
too far. That's the only things I'm interested in messing with. And I'm
looking for the design methodologies that allow me to make these kinds of
alterations. I'm not really wanting to be in the business of designing DE or
spending hours experimenting.

I've yet to determine whether I can classsify using models in an antenna
program as being a "simple design methodolgy" given the kinds of alterations
I might want to make.

6 Do the element length corrections due to use of a metalic boom
assume a
particular element fixing method? Such as through the boom or on top of
the
boom?

No, they *demand* a particular fixing method! (See 3.)

This is a key to understanding for me.