Also... at least for contest operation it is not max gain that is important,
it is making sure there are no nulls in the expected takeoff angle pattern
to your target area. For this area that means making sure there are no
nulls in the takeoff pattern in the direction of Europe, in the range of
expected arrival angles from there.
And yes, there are lots of funny stories... first one is when trying to
break a pileup and getting beaten by all these guys that I knew only had
tribanders on short towers with my 10m antenna at 120', switch to the one at
30' on a ring rotor on the same tower and viola, first call. Also with that
stack with yagis at 120, 90, 60, 30 when running into Europe (when we had
real propagation that is) it was not uncommon to have the loudest western
European signals on the 30' antenna, but eastern Europe might be better on
the 90'+60'(which were always fed together) or the 120' one alone. Now of
course the only 10m antenna that does anything useful is at 180'.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
n1rr@comcast.net
Sent: Tuesday, August 09, 2016 16:53
To: TowerTalk
Subject: Re: [TowerTalk] Stacking question
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@ssvecnet.com>
To: "TowerTalk" <towertalk@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@kk9a.com ; towertalk@contesting.com
Subject: Re: [TowerTalk] Stacking question
On 8/9/2016 7:03 AM, john@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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