[TowerTalk] Stacking question

[n1rr at comcast.net]

The "optimum" stacking distance is related to gain. 
Higher gain antenna require more spacing to prevent the wavefronts from cancelling. 
K1EA suggested back in the 90's to space HF monobanders by approx. 1.5 x BOOMLENGTH 

There's a lot of diagrams in VHF/UHF discussions about using more than one band on a single 
mast that can help you visualize the idea of these wavefronts & pattern interactions. 

HFTA applies optical ray tracing techniques and your input of a single line of your terrain from 
the base of your tower out to several miles beyond it to predict the sums and differences of 
all the rays from all your same-band phased / stacked antennas into a display of resulting 
far-field antenna gain in 1/2 or 1/4 degree increments. 

>From these plots you'll be able to identify nulls or peaks which will be inherited from your terrain 
into your antennas' performance. You'll be able to use this as a tool to evaluate a tower location 
choice by band and by the direction for which you've provided the terrain data. 

Yes, the antenna system's pattern and gain will change as you vary the spacing. For each 
antenna design there will be a spacing that results in the peak forward gain, another will give 
peak FB, and other spacings for other criteria. 

The real guessing game comes when you try to tie propagation to all the above "averaged" data 
(i.e. Terrain plots from 20degs to 65degs averaged over 6 bands blah-blah & 200 hrs later....) 
that you've gathered to optimize your choices. Will next month's propagation be better for the 
two long boom yagis or the 4-stack of mid-sized yagis ? Do I have to move that stack up or down 
next season ? 

K2TR tells a story from the W2PV days about one weekend on 10M or 15M when the best 
antenna all weekend was a simple 70 or 80 foot high 2-stack small of yagis. And we've all 
experienced or read about a given weekends conditions which were described as a "high_ 
antenna_weekend". 

"You can never have enough antennas." is the old saying..... I believe that and that flexibility 
& enough of the right antennas can get you closer to achieving the performance you wish for. 
With time your on-air experience will lead you to modify your beliefs as to what is needed. 
-Charlie N1RR 

----- Original Message -----

From: "StellarCAT" <rxdesign at ssvecnet.com> 
To: "TowerTalk" <towertalk at contesting.com> 
Sent: Tuesday, August 9, 2016 11:38:52 AM 
Subject: Re: [TowerTalk] Stacking question 

These values are what M2 recommends - I assume based on their modeling 
results AND they are based on my own EZNEC modeling results. They work well 
with side and back lobes and achieving a great - well positioned take off 
angle. Added gain is in the area of 2.4 db for the 20 and 2.6 for the 15 
(referenced to the bottom antenna of course) which is about max for those 
heights above ground. Note the 20 is a 50' boom, the 15 a 45'. 

g. 



-----Original Message----- 
From: Richard (Rick) Karlquist 
Sent: Tuesday, August 9, 2016 11:21 AM 
To: john at kk9a.com ; towertalk at contesting.com 
Subject: Re: [TowerTalk] Stacking question 



On 8/9/2016 7:03 AM, john at kk9a.com wrote: 
> I have no HFTA experience however after looking at the stacking distances 
> from people that have used it I would not recommend it. It puts the beams 
> way too close together in my opinion. 
> 
> John KK9A 
> 
> high for you! I've stuck with the M2 recommendations - and have in 
> modeling confirmed they work well. That is 60' on 20 and 45' on 15. The 
> 
> Gary 
> K9RX 
> 

According to my modelling, 60' on 20 and 45' on 15 are near the 
MAXIMUM stacking distances, being nearly a wavelength. Did I 
misunderstand what you were saying? 

Rick N6RK 

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