On Jun 28, 10:36 am, Richard Clark wrote:
On Thu, 28 Jun 2007 06:19:44 -0700, JIMMIE
wrote:

While pondering the design of a broadband antenna that would cover
from 50 to 450 Mhz I considered a log periodic array. This would serve
my purpose but the size would be inconvienent. Then I had a thought,
Could I remove the elements that are not required for amateur band
coverage? In my case I am only interested in 50, 144,and 432 MHz
bands, Would this allow me to shorten the boom by an amout equal to
the space occupied by the removed elements and have a gain of 7Dbd.
Could I cover all 3 bands with just the elements for 6 and 2m?
Any thoughts on this would be greatly appreciaated.

Hi Jimmie,

What you are then asking for is NOT a broadband antenna; but rather a
multiband antenna, or even three, interlaced single band antennas.
Don't try this at home with a gaussian bundle.

To answer your question more directly, yes you can remove those
elements that do not contribute to the three bands. Unfortunately, to
maintain its LDPA aspects, you still have to maintain some outliers
for each band. This doesn't necessarily shorten it, because an LPDA's
length is driven by many other considerations such as bandwidth and
gain, not just simply extremes (yes, that too is part of the mix,
simply a complex part of the mix).

No to your last question. The matter of resonance is still a first
principle. However, the 2M band is loosely related to the 70cM band,
and if you are building an LPDA (and sweep the elements, chevron
style) there may be a chance of it performing there too.

All-in-all, don't expect remarkable gain after having gone through all
these exceptions.

73's
Richard Clark, KB7QHC

Thanks this is what I was expecting but I think I am going to try it
anyway.
Also thanks for not mentioning that the 7Dbd gain would be a little
overly optimistic, I meant dbi. I also realize now that butchering the
the antenna would not save that much in size or material even if it
did work.

Jimmie