On Jun 28, 1:06 pm, "Jerry Martes" wrote:
"JIMMIE" wrote in message

ups.com...





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.
SNIP
Jimmie

Hi Jimmie

Have you figured out which elements to remove and which will remain?

Jerry- Hide quoted text -

- Show quoted text -

In reality it will probably be designed as if it were 2 or 3 single
band lpda antennas. Cebik has a couple of designs like that and I will
just put them on one boom trying them spead out and with the space
removed. For now I am thinking four four element cells for each band.

Im also curious to find out how a swept element 2m antenna will work
on 70cm.


Jimmie