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Thanks to all for your replies. This has been a great learning process.
=20
I will now pass along my experiences, as quite a few of my replies
revealed interest in duplicating this antenna.
=20
The idea for my design came from an article by K5IU and KE7BT in the
Summer 1998 issue of Communications Quarterly. A lot of the theory of
this article is repeated in ON4UN's new book, "Low Band DX-ing", that =
just
came out.
=20
My tower is 192 feet high, made out of 19 sections of Rohn 25 and a =
short
mast with a 5 inch corona ball on top. Insulators of my own design were =
placed
at the 60 foot level. All guy wires are insulated from the tower and =
broken up with
insulators every 50 feet, except the set at the 60 foot level, which are =
154 feet
long, which is 120 electrical degrees on 160 meters. (More on this =
later)
=20
132.5 feet of Rohn 25 is resonant on 1520 khz as installed (base is 60' =
AGL) over
East Texas soil. By making the vertical radiator a bit too long raises =
the feed point
impedance slightly, and allows use of a series capacitor at the base to =
resonate
it to the desired frequency by tuning out the inductive reactance of the =
radiator.
I ended up with a series C of 800 pf to resonate the system on 1830 =
khz. The
series C is placed between the coax center conductor and the base of the =
vertical
radiator. The vswr was 1.24:1 at resonance with a measured impedance at =
the base
of 43 ohms. This is due to the increased length of the vertical radiator =
and the 20 degree
slope of the radials. My next step is to install another series =
capacitor between the
coax braid and the three radials and tune for minimum vswr. The 1.5:1 =
bandwith of
this installation is 145 khz.
=20
Since the radials are floating and elevated, a current balun is =
necessary at the
feed point. (Ferrite beads over the coax) Also 170 uh RF chokes were =
installed
from the base to ground and from the radials to ground to keep the =
system drained
from static build-up. Spark-gap type arrestors are installed accross the =
three base insulators.
If you utilize radials of 45 or 120 electrical degrees, the current will =
be equal on
all the radials and will not change as you QSY around the band. This is =
not true if
one uses quarter wave radials Many have suggested that three elevated =
radials are
not enough, but there is less than 0.3 db difference between 3 and 32 =
elevated radials.
I am concentratig my efforts into a ground screen under the three =
radials to eliminate
all the ground losses I can.
=20
Again, thanks to all who helped, especially L.B. Cebik, who solved my =
problem in
one short note!
=20
(((73)))
Phil, K5PC
=20
=20
=20
I hope this is helpful to those of you who have expressed interest in =
this project.
Experience is a very good teacher!=20
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD W3 HTML//EN">
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<HEAD>
<META content=3Dtext/html;charset=3Diso-8859-1 =
http-equiv=3DContent-Type><!DOCTYPE HTML PUBLIC "-//W3C//DTD W3 =
HTML//EN">
<META content=3D'"MSHTML 4.72.3616.1301"' name=3DGENERATOR>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2><BR> </DIV></FONT>
<DIV><FONT color=3D#000000 size=3D2>Thanks to all for your replies. This =
has been a=20
great learning process.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>I will now pass along my =
experiences, as quite a=20
few of my replies</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>revealed interest in duplicating =
this=20
antenna.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>The idea for my design came from an =
article by=20
K5IU and KE7BT in the</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>Summer 1998 issue of Communications =
Quarterly. A=20
lot of the theory of</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>this article is repeated in ON4UN's =
new book,=20
"Low Band DX-ing", that just</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>came out.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>My tower is 192 feet high, made out =
of 19=20
sections of Rohn 25 and a short</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>mast with a 5 inch corona ball on =
top.=20
Insulators of my own design were placed</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>at the 60 foot level. All guy wires =
are=20
insulated from the tower and broken up with</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>insulators every 50 feet, except the =
set at the=20
60 foot level, which are 154 feet</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>long, which is 120 electrical =
degrees on 160=20
meters. (More on this later)</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>132.5 feet of Rohn 25 is resonant on =
1520 khz as=20
installed (base is 60' AGL) over</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>East Texas soil. By making the =
vertical radiator=20
a bit too long raises the feed point</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>impedance slightly, and allows use =
of a series=20
capacitor at the base to resonate</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>it to the desired frequency by =
tuning out the=20
inductive reactance of the radiator.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>I ended up with a series C of 800 pf =
to =20
resonate the system on 1830 khz. The</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>series C is placed between the coax =
center=20
conductor and the base of the vertical</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>radiator. The vswr was 1.24:1 at =
resonance with=20
a measured impedance at the base</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>of 43 ohms. This is due to the =
increased length=20
of the vertical radiator and the 20 degree</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>slope of the radials. My next step =
is to install=20
another series capacitor between the</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>coax braid and the three radials and =
tune for=20
minimum vswr. The 1.5:1 bandwith of</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>this installation is 145 =
khz.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Since the radials are floating and elevated, a =
current balun=20
is necessary at the</FONT></DIV>
<DIV><FONT size=3D2>feed point. (Ferrite beads over the coax) Also 170 =
uh RF=20
chokes were installed</FONT></DIV>
<DIV><FONT size=3D2>from the base to ground and from the radials to =
ground to keep=20
the system drained</FONT></DIV>
<DIV><FONT size=3D2>from static build-up. Spark-gap type arrestors are =
installed=20
accross the three base insulators.</FONT></DIV>
<DIV><FONT size=3D2>If you utilize radials of 45 or 120 electrical =
degrees, the=20
current will be equal on</FONT></DIV>
<DIV><FONT size=3D2>all the radials and will not change as you QSY =
around the=20
band. This is not true if</FONT></DIV>
<DIV><FONT size=3D2>one uses quarter wave radials Many have =
suggested that=20
three elevated radials are</FONT></DIV>
<DIV><FONT size=3D2>not enough, but there is less than 0.3 db difference =
between 3=20
and 32 elevated radials.</FONT></DIV>
<DIV><FONT size=3D2>I am concentratig my efforts into a ground screen =
under the=20
three radials to eliminate</FONT></DIV>
<DIV><FONT size=3D2>all the ground losses I can.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Again, thanks to all who helped, especially L.B. =
Cebik, who=20
solved my problem in</FONT></DIV>
<DIV><FONT size=3D2>one short note!</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>(((73)))</FONT></DIV>
<DIV><FONT size=3D2>Phil, K5PC</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2> </FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>I hope this is helpful to those of you who have =
expressed=20
interest in this project.</FONT></DIV>
<DIV><FONT size=3D2>Experience is a very good teacher! =
</FONT></DIV></BODY></HTML>
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