Please excuse Pat's previous message about W8AH. He hasn't been
feeling too good lately after the bad accident he had!
>From Frank Donovan <donovanf@sgate.com> Wed Jun 14 01:14:27 1995
From: Frank Donovan <donovanf@sgate.com> (Frank Donovan)
Subject: optimum stacking distance
Message-ID: <Pine.OSF.3.91.950613195606.30698A-100000@holmes.sgate.com>
Hi Kris!
As you are probably aware, serious contesters, both HF and VHF, have been
using stacked Yagis for many years. I've been using them myself on 40 thru
10 meters for over 20 years.
Many excellent articles have been written on the topic, one fairly recent
article is in the ARRL UHF/Microwave Experimenter's Manual (chapter 9). It
describes the relationship between gain, beamwidth and the concept of
"effective area," often referred to as capture area in other texts.
The basic idea is that higher gain Yagis, which of necessity have
narrower beamwidth, also have larger effective areas. In order to obtain
useful stacking gain its important that these effective areas do not
significantly overlap.
A further complication, particularly on HF, is that the individual antennas
in the stacked array inevitably have different patterns and feedpoint
impedances due to their different heights above the ground!
The best way to design a stacked Yagi array is to use an antenna
modelling computer program. I've modelled my HF stacked Yagis for years
with W7EL's ELNEC program. Its very easy to use, and eliminates all of
the guesswork in trying to apply rules of thumb and cut and try methods to
the design of stacked Yagis. By the way, a new version Roy's program, EZNEC
based on the professional NEC2 code, is now available. If you are serious
about stacked Yagi arrays, I'd suggest that you acquire an antenna modelling
program before you build and install the array!
73!
Frank
W3LPL
On Mon, 12 Jun 1995, Kris I. Mraz wrote:
> At HamCom this past weekend I attended the antenna design forum on Sunday. The
> presenter (can't think who it was right now) stated that the optimum
> (vertical) stacking distance between Yagis was dependent on the gain of
> the individual Yagis.
>
> I had never heard of this before so when I got home I looked up Yagi
> Stacking in the ARRL Antenna Handbook. It briefly touched on this by
> stating that the stacking distance was dependent on the *beamwidth* of
> the major forward lobe and referred to a little graph with beamwidth on
> the x-axis and stacking distance on the y-axis. It showed that narrower
> beamwidth antennas must be stacked further apart than broader beamwith
> antennas.
>
> Now, I know that in general higher gain antennas have narrower
> beamwidths. Can someone explain why narrower beamwidth (higher gain)
> antennas must be stacked further apart? Or point me to a book that
> gives the details? tnx.
>
>
> 73
> Kris AA5UO
> mraz@aud.alcatel.com
>
>
>
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