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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"TS" wrote in message
...
Hi all

Was wondering if there is anyone out there who can help? I have just
purchased a 7 element ATN 18-30-7 log periodic that covers 18-30Mhz. I
believe there is another ATN aerial with the same boom length of 6
metres
that covers 14-30Mhz. I was hoping someone with one of these beasts
could
advise the element lengths etc so i can convert mine to cover
20metres. I
assume i will need to rearrange the elements, drill alternate mounting
holes
and change some element lengths and make some crossover straps for
phasing
harnesses but thats just a formality. My aerial comes with a diagram
of the
element lengths etc so was hoping someone could scan and send. I could
start
from scratch and try and design a unit but this would save me a heap
of
time. It appears that ATN is long gone. Any help would be greatly
appreciated. I have quite a collection of amateur radio related
service
manuals in pdf and or jpg format so maybe i can return the favour.

email for reference is

Thanks in advance.
Cheers
Tony
VK2TS