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
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