Dear Tony: You are welcome.
What might, or might not as I have only minimal information, prove
to be the easy way to scale the new elements is to realize that the tips
of the new elements will be close to being in line with the tips of the
"old" elements. This is close enough particularly if, to maintain the
principle of each element being designed to fail with the same amount of
wind/ice pressure, the majority of the ends of the new elements are of
the same diameter as those of the "old" elements. In other words, if
the original antenna was designed to the above principle, the new
elements will look like the longest "old" element with added buts that
are larger. Having the additional boom be the next size larger than the
old boom facilitates this and the splicing of the booms. Consider a
"plastic" rope strut to stiffen the boom.
Ice may well not be a major consideration for you as it is here.
However, a few years of wind induced vibration has a tendency to damage
the places where the longer elements are attached to the boom. Internal
and/or external boom/element sleeves in those areas can extend the
lifetime significantly.
Keep us all posted on your progress. Several of us will be
interested in the specifics of the original antenna.
73, Mac N8TT
--
J. Mc Laughlin - Michigan USA
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"TS" wrote in message
...
Hi Mac

The lengthening of the boom and the further scaling of larger elements
does
sound like a damn good idea ! Thanks for the ideas,,,,much
appreciated.

Cheers and 73's
Tony VK2TS

"J. McLaughlin" wrote in message
...
Dear Tony (VK2TS):
Nice to see a real antenna question from an actual radio
amateur...
It seems to me that two of your choices a
1. Distributing seven elements on the same boom using the same
attachment points. All except the front (smallest) element could be
lengthened by a constant ratio so that the rear (longest) element is
self resonant at about 12 MHz. An estimate for the ratio by which
elements are lengthened may be found by dividing 18 by 14.
Seven elements to cover the octave you are interested in on a
six
meter boom is OK, but a longer boom and a few more elements can
provide
less variation in VSWR with frequency and more gain.
2. It sounds as if the boom you have is of one piece. [One
alternate
scheme for the boom of a LPDA is to construct the boom in two pieces
so
that the boom is also the transposing transmission line.] I say
this
because you mention "crossover straps for phasing."
Thus an alternative is to leave what you have alone and extend
the
boom. Place additional elements along the extension spaced with the
same ratio presently used and having lengths that progress with the
same
ratio presently used. This might involve the least amount of work
and
certainly would produce a better antenna. The extension of the boom
might be a size larger than the present boom so as better to support
the
longer elements and so as to facilitate "splicing" to the present
boom.

Extending is what I would do.
73, Mac N8TT
--
J. Mc Laughlin - Michigan USA
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