[TowerTalk] log periodic antennas

[Bob Nielsen]

On Fri, Jun 22, 2001 at 11:09:01PM +0000, Phil Duff wrote:
> I've been curious about log periodics myself.
> 
> The ARRL Antenna Handbook 17th Ed. has a 5 band (13-30mhz) design on a
> 26 ft boom with 12 elements.
> 
> The article text on pg 10-10 states in part:  "...this is a large
> array....  with the same gain one would expect with a full size
> two-element Yagi array:"
> 
> I acknowledge the benefits of the LP including bandwidth, feed impedance, etc.
> but for a 26 ft boom and 12 elements I'd hoped for more than 2-element
> Yagi performance.

Conventional wisdom says that the longer the boom is and the more
elements the array has, the higher will be the gain.  However in the
case of a LPDA, only a few of the elements (the active region where the
element length is approximately one-half wavelength) are actually
radiating at any one frequency.  This was explained by Isbell in his
1960 IRE article (summarized in W8JK's Antennas, 2nd edition).

There ain't no free lunches; there are only a few inexpensive ones.

73, Bob N7XY

-- 
Bob Nielsen, N7XY                          nielsen@oz.net
Bainbridge Island, WA                      http://www.oz.net/~nielsen
IOTA NA-065, USI WA-028S 

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