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Hi Gregg:
I would be concerned about two things - 1, the continuity and how to =
keep a "loose" piece of coax feeding a tribander and a rotator cable at =
tower potential. 2, the electrical length even if continuity and =
cables are ignored. With the elements floating above the boom, the =
electrical length of the whole thing may be only 80 or 90 feet, which =
will be fine for 80 as a 3/8 wave electrically, but will be quite short =
for 160. =20
As an alternative, consider a piece of non-metalic rope on the mast, =
just below the tribander supporting an inverted L arrangement about 5 =
feet out from the crank-up tower. One can put an 80 meter trap in the =
wire at about 66 feet and have a good antenna on both bands. Being =
resonant on 160, you only have to have an UnUn or L-network to get the =
impedance up to 50 ohms. The latter can be done at the radio, as the =
SWR at resonance will probably be 2 or 3:1 depending on geometry and =
ground losses. On 80, the SWR should be 1.5:1 or less, unless a nearly =
perfect ground exists.
73 Good luck George K8GG
-----Original Message-----
From: W6IZT@aol.com <W6IZT@aol.com>
To: topband@contesting.com <topband@contesting.com>
To: <topband@contesting.com>
Date: Tuesday, October 16, 2001 5:27 PM
Subject: Topband: shunt feeding a crank-up tower
=20
=20
I am in the process of planning my antennas for a new qth. There is =
a 55 ft crank-up already in place with a Force12 C31 xr at 60 ft. I am =
hoping to shunt feed this tower for 160 and 80.=20
=20
I'm sure this has been done before, but I am concerned about feeding =
the tower and the potential for less than perfect electrical continuity. =
As an alternative I have considered running a parallel conductor from =
the top of the tower and grounding it at the base.=20
=20
If you have tried this arrangement, please share your experiences. =
Any feedback is greatly appreciated.=20
=20
73s and see you in the pile-ups=20
Gregg=20
W6IZT=20
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<BODY bgColor=3D#ffffff>
<DIV><FONT color=3D#000000 size=3D2>Hi Gregg:</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>I would be concerned about two things - 1, the =
continuity and=20
how to keep a "loose" piece of coax feeding a tribander and a =
rotator=20
cable at tower potential. 2, the electrical length even if=20
continuity and cables are ignored. With the elements floating =
above the=20
boom, the electrical length of the whole thing may be only 80 or 90 =
feet, which=20
will be fine for 80 as a 3/8 wave electrically, but will be quite short =
for=20
160. </FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>As an alternative, consider a piece of non-metalic =
rope on the=20
mast, just below the tribander supporting an inverted L arrangement =
about 5 feet=20
out from the crank-up tower. One can put an 80 meter trap in the =
wire at=20
about 66 feet and have a good antenna on both bands. Being =
resonant on=20
160, you only have to have an UnUn or L-network to get the impedance up =
to 50=20
ohms. The latter can be done at the radio, as the SWR at resonance =
will=20
probably be 2 or 3:1 depending on geometry and ground losses. On =
80, the=20
SWR should be 1.5:1 or less, unless a nearly perfect ground =
exists.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>73 Good=20
luck George =20
K8GG</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 solid 2px; MARGIN-LEFT: 5px; PADDING-LEFT: =
5px">
<DIV><FONT face=3DArial size=3D2><B>-----Original =
Message-----</B><BR><B>From:=20
</B><A href=3D"mailto:W6IZT@aol.com";>W6IZT@aol.com</A> <<A=20
href=3D"mailto:W6IZT@aol.com";>W6IZT@aol.com</A>><BR><B>To: </B><A =
href=3D"mailto:topband@contesting.com";>topband@contesting.com</A> =
<<A=20
=
href=3D"mailto:topband@contesting.com";>topband@contesting.com</A>><BR>=
To: <topband@contesting.com>
<B>Date:=20
</B>Tuesday, October 16, 2001 5:27 PM<BR><B>Subject: </B>Topband: =
shunt=20
feeding a crank-up tower<BR><BR></DIV></FONT><FONT=20
face=3Darial,helvetica><FONT size=3D2>I am in the process of =
planning my=20
antennas for a new qth. There is a 55 ft crank-up already in place =
with a=20
Force12 C31 xr at 60 ft. I am hoping to shunt feed this tower for =
160 and=20
80. <BR><BR>I'm sure this has been done before, but I am concerned =
about=20
feeding the tower and the potential for less than perfect electrical =
continuity. As an alternative I have considered running a parallel =
conductor=20
from the top of the tower and grounding it at the base. <BR><BR>If =
you have=20
tried this arrangement, please share your experiences. Any feedback =
is=20
greatly appreciated. <BR><BR>73s and see you in the pile-ups =
<BR>Gregg=20
<BR>W6IZT</FONT> </FONT></BLOCKQUOTE></BODY></HTML>
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