<html><head></head><body><div class="yahoo-style-wrap" style="font-family:times new roman, new york, times, serif;font-size:16px;"><div dir="ltr" data-setdir="false"><div><p class="ydp55647da7MsoNormal">I like OCF dipoles because they offer the ability to be
multiband installations which can be fed with a single piece of 50-ohm
coax.<span> </span>I have a one-acre suburban lot, so
I have room for an 80M OCF dipole.<span> </span>The
half wavelength for 80M is about 126 feet, so you need a straight run of that
length.<span> </span>The objective of this
installation was to have as many resonant ham bands as possible with a single
antenna and a single coax feed line.<span> </span>The
OCF is usually cut in a length ratio of 2 to 1.<span>
</span>For 80 meters those lengths are 84 feet and 42 feet.<span> </span>Here are some of the experimental results for
installation of my OCF.</p>
<p class="ydp55647da7MsoListParagraphCxSpFirst"><!--[if !supportLists]--><span style="font-family:Symbol;mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol"><span>·<span style="font-style: normal; font-weight: normal; font-stretch: normal; font-size: 7pt; line-height: normal; font-family: "Times New Roman";">
</span></span></span><!--[endif]-->Make the dipole for the low end of the 80M band.<span> </span>Cut for 3.6 MHz one gets resonances for 7.2Mhz,
14.4MHz and 28.8MHz.<span> </span>It also works on
18.1MHz.<span> </span>These bands can be worked
without an antenna tuner.<span> </span>Most other
bands can be used with an antenna tuner.</p>
<p class="ydp55647da7MsoListParagraphCxSpMiddle"><!--[if !supportLists]--><span style="font-family:Symbol;mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol"><span>·<span style="font-style: normal; font-weight: normal; font-stretch: normal; font-size: 7pt; line-height: normal; font-family: "Times New Roman";">
</span></span></span><!--[endif]-->4:1 baluns are commercially available and are
suitable for a 200 ohm feed point.<span> </span>The
impedance of an OCF is about 150 ohms which indicates a 3:1 balun which is not
generally available.</p>
<p class="ydp55647da7MsoListParagraphCxSpMiddle"><!--[if !supportLists]--><span style="font-family:Symbol;mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol"><span>·<span style="font-style: normal; font-weight: normal; font-stretch: normal; font-size: 7pt; line-height: normal; font-family: "Times New Roman";">
</span></span></span><!--[endif]-->Using a 4:1 balun means you must find the 200
ohm feed point on the 126 foot wire.<span>
</span>Finding the correct lengths for the shorter and longer sections involves
experimentation.<span> </span>My final lengths were
40 feet and 88 feet.</p>
<p class="ydp55647da7MsoListParagraphCxSpLast"><!--[if !supportLists]--><span style="font-family:Symbol;mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol"><span>·<span style="font-style: normal; font-weight: normal; font-stretch: normal; font-size: 7pt; line-height: normal; font-family: "Times New Roman";">
</span></span></span><!--[endif]-->A current balun is required immediately after
the 4:1 balun.<span> </span>The OCF is not a
symmetrical antenna, so there will be rf current trying to go down the shield
portion of the feed line.</p>
<p class="ydp55647da7MsoNormal">If you want a good multipurpose antenna for the principal
ham bands this is a good starting point.<span>
</span>If you only have 66 feet of distance on your property, dividing the
numbers shown above by 2 will give you a 40M OCF.</p>
<p class="ydp55647da7MsoNormal">Thanks to Steve for starting this conversation.<span> </span>His was an interesting and in-depth analysis
of OCF dipoles.<span> </span>It got me to thinking
about my 80M OCF and how I needed to make the theory work at the K1VK qth.</p>
<p class="ydp55647da7MsoNormal">73 de K1VK</p>
<p class="ydp55647da7MsoNormal"><span> </span></p></div><br></div></div></body></html>