[TowerTalk] HF vertical opinions

[Jim Lux]

At 09:28 AM 11/26/2006, Rob Atkinson, K5UJ wrote:
>I don't think the no. of radials and their length affect the angle of
>maximum radiation in the vertical plain anywhere nearly as much as the
>length of the vertical radiator.  the no. of radials and their length affect
>   how much rf gets radiated.  But to avoid resurrecting another argument
>about radials, I will quckly change the subject and say that I also think
>the SteppIR fluid motion whatever-they-are-calling-it-now vertical is the
>way to go.

A few months ago, I did a modeling analysis comparing an approach 
where the length is always the same fraction of a wavelength vs a 
fixed length radiator and a tuning network at the base to match 
it.  I was also looking at trapped verticals (which are sort of a 
special case of the SteppIR sort of thing)

The difference in efficiency is down the sub 1 dB range (i.e. less 
than the variability you'll get from other factors) and varies 
somewhat with frequency and what that fixed length is, and that would 
be a bit more pronounced with "real" tuners.

Probably the only real noticeable difference is that the vertical 
pattern changes (i.e. you radiate the same power, but it's 
distributed differently).  The "always resonant" strategy has a 
pretty consistent pattern (depending on what your far field soil 
properties are), while the "fixed length with tuner" gets a variety 
of lobes, particularly as the frequency goes up.  IF you know what 
angle of arrival your signals are at, then you might be able to 
optimize, but with random arrival angles, I don't know that it makes 
a huge difference.

I would guess (and that's all it is right now, a guess) that you 
could make the choice based on mechanical or installation convenience 
or cost or aesthetic grounds, and not notice a heck of a lot of 
difference in performance.  For myself, I went with the fixed length 
radiator and the tuning network, because it's easier to deploy in a 
portable situation, and I need the tuning network anyway for an 
active phased array.