[TowerTalk] 160-m Inverted L or Sloper?

[K4SAV]

Jerry wrote:
Which means all the wires from the tower have to be connected to the 
tower radial system at the base of the tower.  It also means that all 
wires exiting from the tower act like a radial themselves and will have 
some shield currents(hopefully small if there is a good radial system).  
It also means that any
guy wires have to be isolated from ground. If you don't have a good 
radial system, you can easily be down many dBs below that of a good 
quarter wave vertical.

Tom wrote:
Not exactly. Again it's a matter of random luck. You could have a length 
of tower below the slopper that is 1/4 wl long electrically, and 
electrically very low impedance above the slopper, say from guylines or 
a large stack of antennas. In that case current divides at the shield or 
feedpoint connection junction with most of the current flowing upwards. 
It's all a matter of luck.

Jerry again:
In theory that is true, however, there is a catch 22 situation here. 
With a 1/4 wave below the feedpoint, and no radials, all the wires 
exiting the tower now look like part of the tower.  This now becomes 
impossible to analyze and becomes a luck situation (usually bad). The 
best that can be hoped for is maybe only a dB or two loss, and the worst 
is that the wires from the tower become a significant radiator and add a 
lot of horizontal components that turns the antenna system into a mostly 
straight up radiator with a lot of ground loss.

I was trying to state what was required to make the system efficient 
which is the reason I said you have to have a good radial system. The 
radial system could be elevated or on the ground, but you need something 
to decouple the tower currents from ground and other wires.  With a 1/4 
wave length of tower under the feed point, this does reduce the ground 
currents at the base of the tower, and so for decoupling purposes this 
should reduce the size requirement for the radial system, but it doesn't 
eliminate it.

It is no doubt that a half sloper is a difficult system to analyze, 
which is the reason most people just try it to see what happens.  That 
is the reason the results are random.


Tom wrote:
So much affects the results a slopper (or N4KG feed) is truly just a 
matter of luck what the system behaves like, but one thing is 
clear...it'll never beat a good vertical for gain. The closest to expect 
is a tie.

Jerry again:
Even if you could change the tower to whatever configuration you wish, 
plus have an extensive radial system, the best you can do from a sloper 
is around 1 dB gain, which is very close to what can be achieved with a 
quarter wave vertical. Most sloppers are several dB down from a good 
vertical. There are also cases for very tall towers where the thing 
becomes a high angle radiator and worthless for DX, but most of us don't 
have towers like that, except for maybe Tom.

Jerry, K4SAV