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Re: [TowerTalk] Top loading HF-6V for 160

To: "Jim Lux" <>
Subject: Re: [TowerTalk] Top loading HF-6V for 160
From: "Michael Tope" <>
Date: Sun, 21 Oct 2007 13:10:00 -0700
List-post: <>
----- Original Message ----- 
From: "Jim Lux" <>

> Something along those lines...
> I thought about this a bit yesterday.  4nec2 can alter physical 
> parameters (including the value of the loading inductor), but I'm not 
> sure how to set it up to get what you want in one step.
> You've got a center loading inductor (or, more properly a middle loading 
> inductor), but do you want the feedpoint impedance to be 50+j0, or, are 
> you willing to let the input Z vary, and all you want to do is optimize 
> the radiation efficiency?

I think you'll also want to optimize for minimum feedpoint reactance in 
order to force the loading inductor to a realistic value. Otherwise, 
depending on how sensitive your excitation source is to mismatch, the 
optimizer may try to zero out the inductance to maximize efficiency. 

> SO your optimization parameters would be the length of the top hat 
> wires, and the angle you take them off at, the position of the center 
> loading inductor, and its inductance.  You'd optimize for field strength 
> (for a constant excitation power) at some low elevation angle, I assume?
> You could run several optimizations with different tophat topologies 
> (3,4,5 wires, whether or not they're spiderwebbed, etc.)
> This is an interesting optimization problem.. clarify what you're 
> looking for and I'll grind on it a bit more.

For the portable operating scenario where you only have one support,
but lots of real estate, you could probably assume a fixed top-hat angle
(say 60 degrees relative to the vertical). The vertical height would be
fixed as well. Too keep it simple, I would use a fixed number of top-hat
wires (say 4). To summarize:

Fixed Parameters:

1) Radiator Height (34ft for the HF2V case)

2) Top-Hat Angle (60 degrees relative to vertical seems like a practical 

3) Ground Loss Resistance [I suggest running two separate cases - 
very good ground ground system (2 ohms) and modest ground 
system (10 ohms)]

4) Inductor Q (200 is a practical number)

Variable Parameters:

1) Inductor Position (0% = base load; 90% = close to top-hat)
2) Inductor Value 
3) Top-Hat Wire Length

Optimization Goals:

1) Minimize Feedpoint Reactance (this will force the inductor to a value 
that will resonate the system). Don't worry about feedpoint resistance. 

2) Maximize Low Angle Radiation (the angle of peak radiation will be 
a function of the ground parameters and can easily be determined 
with a few trial runs)

This is essentially what I was doing manually with EZNEC/Multinec 
(very tedious). There may be a way to use Excel/Multinec to goal seek, 
but I don't have the time right now to mess with it. 

If you can get this to work, it would be worth writing up as it would be
a useful tool for folks comtemplating short low-band antennas. 

73, Mike...........


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