[TowerTalk] 160-m Inverted L or Sloper?
w8ji at contesting.com
Mon Nov 14 11:52:25 EST 2005
I always try my best to not make a technical discussion
personal. These aren't our sisters or mothers, they aren't
deities, they are only pieces of wire. With that in
> No, the only real answer is to try a half sloper (Tom
> calls them sloppers) yourself.
I think slopper is an accurate description that paints a
clear picture of what the antenna actually does. This
antenna, a 1/4 wl worked against a tower, depends heavily on
random blind luck to function. It often does not work at all
because of bad happenstance, because it is indeed a "sloppy
system". Slopper is actually more accurate than "sloper"
because the sloping wire we "think" is the antenna often
does not function as the major radiating part of the system
>You forget that a lot of the worlds
> inventions, discoveries were/are made by accident.
That is called the Edisonian method, if it is by controlled
trial and error. But this antenna is easily explained and
understood with only a very simple understanding of
transmisssion lines and antennas. Any two conductor
transmission line, even coax, must have exactly equal and
opposite phase currents entering and leaving the two
terminals at each end to function properly. As a matter of
fact the very design of coax and the rules of transmission
line theory dictate that the inside of the shield ALWAYS
carries an equal and opposite current from that in the
center conductor, once the shield is several skin depths
There is no question at all about that, and it is not open
for debate. The rules were made to fit the observed behavior
of the line.
The minute you connect the shield (or the center conductor )
of the cable to the tower, the overall tower structure has
**exactly** the same current leaving that point as the
sloping wire does. In the sloping wire, we know the current
decreases. In the tower, the current level can **increase**
as it leaves the transmission line junction. Since radiation
is a function of in line spatial ampere-feet, the tower very
easily can be the dominant radiator of our signals.
The actual range of possible effects is from the slopper
antenna almost not working at all to working just about like
a shunt fed tower of the same height with sloped feed. The
thing unpreditable is what the random towers behave like.
They dominate the uncertainty of the antenna, and since they
can't generally be controlled (no one in his right mind is
going to install a $5000 tower a certain way just so a $5
wire sloping will work properly) it winds up being a blind
> I have two half slopers feed off the same tower, one
sloping east and
> the other west. One of the advantages they have over a
> they have directivity in the direction of the slope.
> advantage is that you do not need another tower. Another
> is they are relatively inexpensive compared to a vertical.
But that is **YOUR** tower Doug, not **HIS** tower.
You also won't find anyplace where I said a slopper doesn't
"work". All I've said is it is unpredictable, a sloppy
system. Anyone installing a slopper should know that if it
works at all or how it behaves with changes depends solely
on the tower it is mounted on.
Let's not make it a personal issue of blind faith, because
they function according to all the rules of transmission
lines and antennas.
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