[TowerTalk] Half Sloper recommendations - Results!

Sat Jan 2 12:45:11 PST 2010

Dick:
I know this is a late addition, but would like to add my experience with a
80/160m 'half' sloper.
I have a aluminum fold-over tower that is 85ft tall, with a SteppIR 3
element with the 30/40m dipole kit.
I have mounted a 75 ft long 80m half sloper from it at about the 72 ft
level.  
It comes off the tower at about a 45 deg angle, and ends about 20ft above
ground. 
It is resonant at 3790 kHz with the SteppIR set to 15m.
The key to my installation is that the SteppIR elements are grounded to the
boom/tower, and can be used to tune the resonant frequency of the Sloper,
i.e. a variable top hat)
To operate a the low end of 80, I set the SteppIR to 40m.
To operate it on 160m, I studied the feed impedance at 1825 as I varied the
SteppIR, and found Z = 50-jX when the SteppIR is set to 6m.
I added a High Q loading coil and HV relay at the feed point, which I switch
in when I operate 160m.
With this set up I can operate a matched antenna on 160, 80 & 75m with one
sloper. 
It is a noisy antenna for receive, and a year ago I added a set of K9AY
loops for a low noise Rx antenna.
My country count currently stands at (worked/confirmed): 80m: 186/157;
160m:124/117, the last 20 to 30 have been added after the RX antenna was
added. 
I do not have any significant radials down, but in North East Texas we are
blessed with highly conductive soil. 
I rarely fail to work anything I can hear, usually with just 200W (I only
kick on the linear when the going gets tough).
Good Luck with whatever you decide.
73s

Bob, W5LT

-----Original Message-----
From: RLVZ at aol.com [mailto:RLVZ at aol.com] 
Sent: Friday, January 01, 2010 11:57 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Half Sloper recommendations - Results!

Hi Guys,

Happy New Year!

Thank You to 10 people who replied concerning my questions about  
installing a 160-meter "Half Sloper" or moving my Inv. L from my 90' tower
(where it 
works poorly) over to my 60' tower.  Your comments  are much appreciated 
and gave good direction!  My original post  is shown below in case anyone 
missed it and wonder what I'm talking  about.  

Basically, I had two questions:

1) Should I install a Half Sloper on my 90' tower and if so how could I do  
so and maximize radiation efficiency?    

2) Since my Inv. L works poorly on my 90' tower due to  heavy tower 
interaction... should I move this Inv. L to my 60' tower  rather than use
the 
Sloper at 90'?

RESULTS OF THE 10 REPLIES:

-1 VOTE TO INSTALL SLOPER ON THE 90' TOWER BUT "BE SURE TO USE  RADIALS".

-2 VOTES TO INSTALL INV. L ON THE 60' TOWER AND IT WILL DO BETTER THAN THE  
90' TOWER DUE TO LESS TOWER INTERACTION.

-2 VOTES TO INSTALL AN INVERTED VEE ON THE 90' TOWER.  (INTERESTING AS  I 
DIDN'T LIST AN INV VEE IN THE OPTIONS.  I HAVE USED INV.
    VEES AT THIS LOCATION FOR YEARS AND THEY WORK PRETTY  WELL IN THAT I 
CAN USUALLY WORK EVERYONE I CAN HEAR)

-5 VOTES TO "SHUNT FEED" THE 90' TOWER.  (VERY INTERESTING AS I DIDN'T  
LIST "SHUNT FEED" AS ONE OF MY OPTIONS!)

CONCLUSION:

Since 5 out of 10 responders said I should "Shunt Feed the 90' tower it's  
clear direction that my next project will be to "Shunt Feed the 90' tower.

What really cinched it is that I didn't include "Shunt Feed" in the 2  
options I was considering and yet it got the most votes!  So for those who
are 
interested in improving their 160-m. performance like me... you might want  
to try "Shunt Feeding" one of your towers.

Shunt Tower Feed Questions:

1) My 90' tower is a self-supporting aluminum tower with a top mounted  
Tribander.  (no guy wires)  The five responders who said I should  "Shunt
Feed 
that 90' tower" recommended I attach the shunt at various  heights ranging 
from 30' to 90' up on the tower and adjust as needed.   QUESTION 1: Will 
using a different attachment height and wire spacing  only effect the
loading 
and bandwidth or is there an attachment height that  will provide better 
radiating efficiency?  

2) I'd like to try a "Slant Feed" as many old AM Broadcast  towers use.  
For one thing, it would make installation quicker and with  less climbing as

it wouldn't need PVC insulators keeping  the shunt wire equally spaced.  
QUESTION 2: Is the "Slant Feed" likely  to tune and radiate about the same
as a 
common 'Shunt Feed" with equally  spaced wire parallel to the tower?  
QUESTION 3: Is there any general  rule of thumb for where to attach a "Slant
Feed" 
on a 1/4 wavelength  tower?  Such as, 25% up the tower above ground level?  
(I've  seen a couple 1/4 wave AM Broadcast towers and it seemed like  the 
Slant Feed wires were connected about 25% of the way up the tower  from 
ground... so perhaps aprx. 25% is the general rule of thumb?)  

Thanks again guys... you're a wonderful help!  

73,
Dick- K9OM

Hi Guys-

I'd appreciate your recommendations on building a Half  Sloper for  160-m.  
I realize that some folk have had excellent  results with Half  Slopers and 
others have had terrible results with  them!  That's why I'm  asking for 
advise on how to construct my  Half Sloper!

Question 1: Most antenna articles say when constructing an  Inv. Vee is  to 
keep the minimum angle between wires at 90 degrees or  greater.  Since  
Half 
Slopers almost never have a 90 degree angle  between the sloper wire and 
the  
tower is this one reason why many Half  Slopers don't work very well... 
lots 
of signal cancellation?

Question  2: I have a 90' tower with a Tribander on top which makes it very 

close to a 1/4 wave for 160-m.  I installed an Inverted L on this   tower 
with 85' vertical and the Inv. L radiating efficiency is very   poor due to 
heavy coupling between the Inverted L and the  tower.   (some models say 
that 
alot of RF is shorted right to  ground!)   Therefore, I am thinking of 
going 
with a Half Sloper  connected near  the top of the 90' tower with the 
sloper 
wire running  NE towards  Europe.  If I anchor the end of the sloper wire 
about 
200' from   the tower the angle is only going to be about 45 degrees.  Do 
you  think  this will work any better towards Europe than my heavily 
coupled  
and inefficient  Inv. L?  (another weakness with my Inv. L is that  I have 
a 
minimal  radial system as it must be pulled up each  Spring).

Question 3: Rather than build the Half Sloper on the 90'  tower  would an 
Inv. L on my 60' tower with 55' vertical and the rest  horizontal  running 
NE 
towards Europe likely outperform the Half Sloper  at 90' towards  Europe... 
keeping in mind that this is a temporary  antenna so I can only  put down a 
minimal radial system as the radials  need to be removed  in Spring.  

I realize that I'm likely to  get a variety of opinions on this and that is 

fine!  Please let  me know which of the above options you believe  is most 
likely to  provide the best 160-m. signal towards Europe.

Happy New  Year!

73,
Dick- K9OM
Edgewater,  Florida