[TowerTalk] Stacking Antennas

[Bob Alexander]

jimlux wrote:
> 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.
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>   
There is a good article on stacking dissimilar antennas on the array 
solutions website.
w5ah