The point with sloppers is unless you plan the system, you
are depending on sheer luck.
1.) The tower connection point at the shield ALWAYS, no
exceptions, has the same current flowing into the sloper
wire. How that current divides and where it goes, and
whether it increases or decreases as you move away from that
point depends on what else is on the tower and how that
stuff is connected.
2.) I don't think anyone said (and I certainly did not say
it) that sloppers can't on occasion "work", or at least make
people feel warm and fuzzy about their antenna.
3.) I did try, first in real life and then years later
looking at it in models, to do a system that had gain. I
could build a system that had F/B, but not one with any real
"gain". Not saying it can't be done, just making the point
that good F/B does not mean you have gain.
> If a quarter wave sloper is merely a method for feeding a
tower.....
> what happens if you have multiple 'slopers', like radials
around the
> tower?
Depends on how they are connected and to a lesser extent
what else is on the tower. As a general rule the more
"stuff" on the tower making a low impedance to terminate the
other half of the feedline the better your luck will be.
> K3ANS has an "inverted sloper system"....where the tower
is fed
> against an array of quarter waves symmetrically placed
around the
> stick. I think there are 8 of them. The tower is 120',
with 3 el 40 on
> top. Sloper height is 80' or so, although my recollection
is hazy
> at this point.... The center conductor of the coax
connects to the tower,
> and the shield to the slopers, or radials, or whatever
they are.
Case in point, a lot of "stuff". In my case with a lot of
"stuff", no luck at all.
> With respect to having the high current portion of an
antenna in the air... Cebik says
> it's important. The higher, the better. But we also
have to realize that
> 50' is not high at 1.8MHz. Neither is 100'. 130' is
quarter wave...and twice
> that wouldn't be considered 'high', for a horizontal
antenna....merely acceptable.
So many BC stations with so many engineers over the years
looking at them doing so much wrong! Seriously, ever wonder
why there isn't a larger effort to move current up in AM BC
towers? The reason is, the current maximum location makes
almost no difference at all as long as they have a good
ground system.
Models are OK, but I think a good part of understanding
antennas should include actually building and using various
antennas and actually trying to work stuff with them. I can
model things all day that don't work out in real life. It
has to be a combination of both.
Absolutely the worse place to use a model is to determine
what happens with losses in the ground. That's why I prefer
to see something near earth actually measured and don't
trust conclusions of models alone.
These "current at the top" verticals started in the 1960's.
W2IU used to run one back then. I tried them for years
myself. Without a FSM that resolves to a fraction of a dB
you'll never measured the difference unless the ground
system is pathetic.
The actual BEST place for highest radiation resistance is
maximum current in the middle. It's ampere/feet, not peak
current height, that matters.
73 Tom
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