[TowerTalk] Stacking Antennas

[jimlux]

Cqtestk4xs at aol.com wrote:
> In a message dated 3/26/2009 5:39:51 PM Greenwich Standard Time,  
> nq4u at mtars.org writes:
> 
> Plans  are to add a stack match. 
> 
> Both antennas will be fed with 75 ohm  hardline cut to proper length. Wire
> antennas will also be located on this  tower.  
> 
> Will there be some pattern distortion due to different  antenna spec's? 
> 
> What are some problems that others have had in  stacking two different
> antennas such as these?
>  
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> 
> 
> 
> Anecdotal here:  
>  
>>From what I've heard stacking dissimilar Yagis has been met with mixed  
> success.  I'm not sure of the reasons.  Boom length and phasing  problems come to 
> mind.
>  
> I've been stacking IDENTICAL antennas since the 80's and have always been  
> successful.
>  
>


I think a way to summarize this is that stacking dissimilar antennas is 
trickier (i.e. less predictable from casual analysis) than stacking 
identical ones.  Identical ones have easier analysis math to predict 
what they'll do.  Dissimilar ones will have "different" patterns as you 
switch the various configurations.  It will probably work (and 
realistically, you may not be able to identify any differences, since 
it's not like you can A/B it).

You could probably, without a huge amount of trouble, run some models in 
NEC to see what you'd get, pattern wise.