One caveat for "terrain analysis" is that HFTA does not model stacks
well around 1/4 wl and less separations. So that leaves NEC/EZNEC
which does give accurate results but over flat terrain. It will also
provide better gain and elevation patterns and for the specific antenna
rather than the HFTA generic "point source" model. The ability to
model interactions with other antennas is pretty useful. I modeled my
stacks both ways.
Is somebody out there reprogramming the "dusty deck" Fortran HFTA for
the 21st century? A worthy project now that we all have beyond Cray
super-computer laptops.
Grant KZ1W
On 3/13/2018 10:12 AM, Bob Shohet, KQ2M wrote:
I respectfully have to disagree with Steve on this.
Stacking with a lower antenna is highly unlikely to produce a lower wave angle. So a
Full-sized 3L will still be almost always superior to a 2L at the same height and that
extra 1 – 2 db at the right angle at the right time with the full-sized 3L
antenna could be significant. What stacking might give you is a higher (than the 3L)
wave angle that is useful to some population area of contesters that you will now be
louder into. And it will give you potentially three different wave angles to choose
from if you phase them and have Upper, Lower or Both switching. However, you will
have a less broadband antenna with reduced F/B and F/S which could handicap you when
dealing with qrm and qrn.
And you will have to put that 2nd antenna very low to get meaningful wave angle
choices and those wave angles may not be very useful especially for working DX.
Every qth is different – with different topography, terrain and other factors to take into
consideration. Everyone should do extensive modeling with your own specific terrain BEFORE
seriously considering stacking a 2nd antenna to see if it is even worth considering. And you also
need to consider the additional wind load on the tower and whether or not what you have up in the
way of tower and guys will support that additional “wind-sail”. :-)
73
Bob KQ2M
From: k7lxc--- via TowerTalk
Sent: Tuesday, March 13, 2018 12:54 PM
To: bmarx@bellsouth.ne ; towertalk@contesting.com
Subject: Re: [TowerTalk] add a 3rd el to 40-2cd
With one antenna at 72 ft why not just add new antenna lower on the tower>?
One of my all time favorite ideas. Stacked would give you similar performance to a full sized 3L plus you get angle and directional diversity. And you don't need expensive rotators! Like my old buddy Mark, AA6DX sez: "Worky, worky!"
Cheers,
Steve K7LXC
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