[Towertalk] stacked LPDA's

n4kg@juno.com n4kg@juno.com
Wed, 20 Mar 2002 23:14:46 -0600


On Wed, 20 Mar 2002  "jljarvis" <jljarvis@abs.adelphia.net> writes:
> 
> Tennadyne has modelled stacked lpda's, and offered
> a few words of wisdom today.
> 
> 1)  you can expect 2.2dB from stacking any pair of
> antennas. 

Sounds reasonable.   N4KG

>  if you're not careful about matching the
> common point impedance, you can lose 1 dB of that.

How did they come up with that number?
At worst, I would expect a 2:1 SWR.
If your feedline loss is low, that will NOT 
result in 1 dB of additional loss.   N4KG

> It almost doesn't pay to bother.

Most stack users would disagree with that conclusion.  N4KG

> 
> 2)  By stacking...depending on height....you will
> clean up the pattern, and suppress high angle lobes.

True.  N4KG

> You will also RAISE the lower lobe of the in-phase system
> by a couple of degrees.  

HUH?  Clarify that statement please.   N4KG
> 
> 3)  It was their opinion that getting a single antenna higher
> would almost always be better than a stack.  Until you want to use 
> it for sweepstakes.  
> 

Here we go again...Higher is NOT always better, even for DX,
especially during the day.  You need BOTH high and LOW
antennas to cover ALL the angles supported by the ionosphere.
(I've lost count of the number of times I've given this sermon)
N4KG

> 4)  My conclusion was that a single antenna, with the ability to
> modify its height, was probably a better solution.  
> 
The BETTER solution is to have HIGH and LOW antennas
that can be switched instantaneously.    N4KG

(I'm getting less and less impressed with the technical
understanding of your contact at Tennadyne)

> 5)  Tilting the lpda's, so as to approximate 1/2 wave spacing at all
> frequencies, probably isn't worth the effort.  But it bears 
> modelling, just as each of the other solutions and heights do.

N4KG:  I especially agree with the last sentence.
 
> Thanks again, for all your inputs.
> 
> Jim Jarvis
> N2EA
> 
> 

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