<div dir="ltr"><font size="4">Thanks for replies.</font><div><font size="4"><br></font></div><div><font size="4">Something I wanted to mention in my discussion but left it omitted was:<br></font><div><font size="4"><br></font></div><div><font size="4">If a 200 ohm feed point impedance is targeted, then i</font><span style="font-size:large">t seems a single 1:4 current balun could be used, instead of the method that MFJ uses and the method I sa</span><font size="4">w employed in one of A</font><span style="font-size:large">RRL Antenna Books where two devices are employed in series, the first being a 1:1 current balun, followed by a 1:n or 1:4 transformer.</span></div><div><span style="font-size:large"><br></span></div><div><span style="font-size:large">It has been a while since I studied Sevick's work, but baluns with ratios between 1:1 and 1:4 are discussed in his work. I can try to locate an example.</span></div><div><span style="font-size:large"><br></span></div><div><span style="font-size:large">The simple, easy to build baluns will have turns ratios of 1:n where n is an integer, 1, 2, 3, ... . Thus you see commercially available baluns with impedance ratios of 1:1, 1:4, 1:9 which are: 50 ohm : 50 ohm, 50 ohm : 200 ohm, 50 ohm : 450 ohm.</span></div><div><span style="font-size:large"><br></span></div><div><span style="font-size:large">Paul, K1VK, talks about a feed point impedance of 150 ohms and as he said this is a ratio of 1:3. I will try to locate an example of a balun which is in that range. I think these are not commercially available, and this is why hams live with the 1:4 balun. A question I have is: If a 1:4 balun is used, is it best to find the 200 ohm feed point on the dipole, rather than the customary 1/3, 2/3 split?</span></div><div><span style="font-size:large"><br></span></div><div><span style="font-size:large">In my second example in my discussion, the impedance transformation is 50 ohm to 139 ohm, which is a ratio of 1:2.8.</span></div><div><span style="font-size:large">I am wondering if the method which employs two devices in series is favored by comercial antenna manufacturers for some reason. Maybe the reason is that it is easier from a manufacturing standpoint to do it this way, rather than manufacturing a 1:n balun, where n is not an integer. </span><span style="font-size:large">You see this in the third example I gave in my discussion, the OCF vertical dipoles by Cushcraft and Hy-Gain. </span></div><div><span style="font-size:large"><br></span></div><div><font size="4">73's</font></div><div><font size="4">Steve</font></div><div><font size="4">AC1EX</font></div><table cellpadding="0" class="gmail-cf gmail-gJ" style="border-collapse:collapse;margin-top:0px;width:auto;font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:14px;letter-spacing:0.2px;display:block"></table><div><span style="font-size:large"><br><br></span></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Dec 6, 2020 at 11:11 AM <<a href="mailto:apizer@comcast.net">apizer@comcast.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Google n1iw ocfd presentation<br>He taught a class on this and also Balun construction at bars we built them as a class project<br>Sadly mike is now sk and and left us way to soon<br>RIP om mike<br><br>Art<br>Nf1a<br><br><br><br>Sent from Xfinity Connect App<br><br><br><br>------ Original Message ------<br><br>From: Paul Pellegrini via bars<br>To: W1hh<br>Sent: December 6, 2020 at 10:33 AM<br>Subject: [bars] Construction of an 80M OCF antenna<br><br><div><div style="font-family:"times new roman","new york",times,serif;font-size:16px"><div dir="ltr"><div><p>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><span style="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>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><span style="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>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><span style="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>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><span style="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>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>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>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>73 de K1VK</p>
<p><span> </span></p></div><br></div></div></div>_______________________________________________
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