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<TD style="FONT-FAMILY: " bgColor=#ffffff width=650 colSpan=3
align=middle><SPAN style="FONT-FAMILY: " class=ObjectCopyRed><B
style="FONT-FAMILY: "><FONT face=Arial><FONT style="FONT-SIZE: 9pt"
color=#ff0000>A 4:1 Air-wound Balun</FONT></FONT></B></SPAN><BR><BR><IMG
border=0 alt=""
src="http://combotec.com/projects/balun14/images/Balun14.jpg" width=400
height=157></TD></TR>
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<TD style="FONT-FAMILY: " class=ObjectCopy vAlign=top colSpan=3>
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<FONT face=Arial><FONT color=#111111><FONT style="FONT-SIZE: 9pt">Since
some time I have been using the Diamond CP6 multiband vertical for my HF
activities. While this antenna performs well on 6m, 10m, 15m and 20m and
also does a reasonable job (for it's length) on 40m, it does not work at
all - for me anyway - on 30m and 17m. The latter is one of my more
favourite bands to listen on, so it was time to do something about it.
Even though my LDG AT-100Pro automatic tuner keeps the IC-7000 happy while
transmitting on 17m, the signal does not really get out and reception is
poor.</FONT><SPAN class=Apple-converted-space><FONT
style="FONT-SIZE: 9pt"> </FONT></SPAN></FONT></FONT><BR><BR></TD></TR>
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<TD style="FONT-FAMILY: " vAlign=center width=165><IMG border=0 hspace=40
alt="LDG AT-100Pro"
src="http://combotec.com/projects/balun14/images/at100pro_thumb.jpg"
width=165 height=56></TD>
<TD style="FONT-FAMILY: " class=ObjectCopy vAlign=top colSpan=2><FONT
face=Arial><FONT color=#111111><FONT style="FONT-SIZE: 9pt">My home has an
attic and that was big enough to string some wire up. I decided to have a
play around with a 17m long deltaloop fed with openwire feeder. The feeder
was salvaged of an old G5RV given to me by a friend (thanks Hennie).
Theoretical calculations show the impedance of a deltaloop cut at its
fundamental frequency to be 150 Ohms when fed from the side. So using this
setup, I was in need of a 4:1 balun to present the AT-100Pro with a more
reasonable load and at the same time transform the balanced line back to
unbalanced.</FONT><SPAN class=Apple-converted-space><FONT
style="FONT-SIZE: 9pt"> </FONT></SPAN></FONT></FONT><BR><BR></TD></TR>
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<FONT face=Arial><SPAN style="FONT-FAMILY: " class=ObjectCopyRed><B
style="FONT-FAMILY: "><FONT color=#ff0000><FONT
style="FONT-SIZE: 9pt">Definition :</FONT></FONT></B></SPAN><FONT
style="FONT-SIZE: 9pt"><SPAN
class=Apple-converted-space> </SPAN></FONT><SPAN
style="FONT-FAMILY: " class=ObjectCopy><I><FONT style="FONT-SIZE: 9pt"
color=#111111>A balun is a device that joins a balanced line (one that has
two conductors, with equal currents in opposite directions, such as a
twisted pair cable) to an unbalanced line (one that has just one conductor
and a ground, such as a coaxial cable). A balun is a type of transformer:
it's used to convert an unbalanced signal to a balanced one or vice versa.
Baluns isolate a transmission line and provide a balanced
output.</FONT></I></SPAN></FONT>
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</TD></TR>
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<TD style="FONT-FAMILY: " vAlign=top width=211><BR><IMG border=0 alt=""
src="http://combotec.com/projects/balun14/images/balun14s1.jpg" width=211
height=113></TD>
<TD style="FONT-FAMILY: " with="10"><FONT face=Arial><FONT
style="FONT-SIZE: 9pt"> </FONT></FONT></TD>
<TD style="FONT-FAMILY: " class=ObjectCopy vAlign=top width=450><BR><FONT
face=Arial><FONT style="FONT-SIZE: 9pt" color=#111111>Quite often toroids
are used to make baluns with. Even a ferrite rod from an old AM radio can
be used. I however have something against using ferrite materials in
baluns. If you are not carefull, the ferrite can get saturated and heat
up. You won't be the first blowing up a balun when using QRO. So instead
of ferrite, I went with an air-wound balun.</FONT></FONT></TD></TR>
<TR>
<TD style="FONT-FAMILY: " vAlign=top colSpan=3><SPAN style="FONT-FAMILY: "
class=ObjectCopy><BR><FONT face=Arial><FONT style="FONT-SIZE: 9pt"
color=#111111>This air-core balun is wound using the following components
:</FONT></FONT>
<UL>
<LI><SPAN style="FONT-FAMILY: " class=ObjectCopy><FONT face=Arial><FONT
style="FONT-SIZE: 9pt" color=#111111>40mm diameter grey PVC pipe with a
length of 9.5cm</FONT></FONT></SPAN>
<LI><SPAN style="FONT-FAMILY: " class=ObjectCopy><FONT face=Arial><FONT
style="FONT-SIZE: 9pt" color=#111111>2 endcaps 40mm
PVC</FONT></FONT></SPAN>
<LI><SPAN style="FONT-FAMILY: " class=ObjectCopy><FONT face=Arial><FONT
style="FONT-SIZE: 9pt" color=#111111>Simple zip cord (multi-stranded
core insulated wire)</FONT></FONT></SPAN>
<LI><SPAN style="FONT-FAMILY: " class=ObjectCopy><FONT face=Arial><FONT
style="FONT-SIZE: 9pt" color=#111111>8 turns bifilar
wound</FONT></FONT></SPAN>
<LI><SPAN style="FONT-FAMILY: " class=ObjectCopy><FONT face=Arial><FONT
style="FONT-SIZE: 9pt" color=#111111>2 banana type chassis
connectors</FONT></FONT></SPAN>
<LI><SPAN style="FONT-FAMILY: " class=ObjectCopy><FONT face=Arial><FONT
style="FONT-SIZE: 9pt" color=#111111>1 SO239
socket</FONT></FONT></SPAN></LI></UL></SPAN></TD></TR>
<TR>
<TD style="FONT-FAMILY: " class=ObjectCopy vAlign=top colSpan=3><FONT
face=Arial><FONT style="FONT-SIZE: 9pt" color=#111111>When fed with the 50
Ohm coax from the AT-100, the balun transforms this impedance to 200 Ohms
which is close to matching 150 Ohms. The image below shows how to wire the
balun :<SPAN class=Apple-converted-space> </SPAN><BR><BR><IMG
border=0 alt=""
src="http://combotec.com/projects/balun14/images/balun14-construction.jpg"
width=387 height=376><SPAN
class=Apple-converted-space> </SPAN><BR><BR>Terminals B and C are
wired to the banana chassis connectors for hooking up the feedline. The
SO239 terminal center pin is wired to C and it's shield to D. Make sure to
connect D and A together. As can be seen on the image at the top of this
page, the wiring enters the PVC pipe and all connections are made
internally. In my case - since I am using the balun inside - I did not
glue the endcaps to the pipe but used a couple little screws instead. This
way the balun is easy to service should the need arise.<SPAN
class=Apple-converted-space> </SPAN><BR><BR>Good luck constructing
yours !</FONT></FONT></TD></TR></TBODY></TABLE>
<DIV></SPAN></SPAN> </DIV>
<DIV><A href="http://combotec.com/projects/balun14/balun14.html"><FONT
face="Times New Roman">http://combotec.com/projects/balun14/balun14.html</FONT></A><FONT
face="Times New Roman"> <FONT face=Calibri><BR><BR>73’s.<BR>Carlos,
CT1GFQ<BR></FONT></FONT></DIV></DIV></DIV></BODY></HTML>