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<font face="Verdana">Hiya Geoff,<br>
<br>
Apparently I qualify as being 'of a certain age'. ;-) I def.
remember 'rabbit ears' and the gyrations folks went through to
pick up those 2 or 3 channels.<br>
<br>
I did those separate measurements to validate that the DE was even
close to right before I proceeded with the rest of the build.
Based on the various replies I've read the director spacing is
likely a bit off as well as the fact that I can not feed it
directly with 50m coax and expect a 1:1 match.<br>
<br>
I'm going to try it with, and without, the director this wkend to
see if it makes a significant difference. I'll leave the match to
the rig's built in ATU for now.<br>
<br>
I'll put the nanoVNA back on it later and check the match across
the band. I was focusing on the FT8 section when doing initial
tests.<br>
<br>
So far, without the director the performance is less than grand on
FT8. I've got it about 10ft above ground on a mast strapped to my
deck railing. ;-)<br>
<br>
73,<br>
<br>
Tim - KC1RET<br>
</font><br>
<div class="moz-cite-prefix">On 9/10/2022 10:10, Geoffrey Feldman
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:004901d8c51f$0a6f1620$1f4d4260$@comcast.net">
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<div class="WordSection1">
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">People
of a certain age might remember Rabbit ears. Folks would
do all kinds of weird things to get the station we wanted.
Lengthening, shortening, adding bits of aluminum foil.
Almost nobody understood antenna resonance but they had some
idea of changing the antenna made it better or worse. The
other humorous factor is that stepping away from the
antenna, might make it worse again. Often friends and
relatives were forced to stand next to the antenna, unable
to see the screen so the rest of us could see whatever.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Impedance
depends on frequency. That depends on what else is nearby
the antenna. The director and reflector, as is everything
around, part of the SWR. Measuring the driven element
alone or measuring it with the reflector, then adding the
director is a waste of time in a Yagi. Put the antenna
together as designed for the band you want, then measure.
Also make your measurements with the antenna at the height
and in the environment you anticipate. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">It
would be interesting to know if the 2.5:1 is true for all 6m
frequencies. The impedance will not be the same at all
frequencies either. That’s also not a horrible SWR, not
great but not horrible. A tuner can compensate for the
rest. Isn’t there a function in the nano to chart impedance
/ SWR across an entire band? If someone has a rig-expert
that can do it for sure.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">-73-<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">W1GCF<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Geoff<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">
bars [<a class="moz-txt-link-freetext" href="mailto:bars-bounces@w1hh.org">mailto:bars-bounces@w1hh.org</a>] <b>On Behalf Of </b>Tim
KC1RET<br>
<b>Sent:</b> Saturday, September 10, 2022 9:54 AM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:bars@w1hh.org">bars@w1hh.org</a><br>
<b>Subject:</b> [bars] Impedance of yagi<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<div>
<p class="MsoNormal">So I'm trying to throw together a 3el
6m yagi for the VHF contest this weekend. I built one
based on a design for a wire + PVC beam I found on da
Google (<a href="http://ehpes.com/n6mw/WireYagi2.pdf"
moz-do-not-send="true" class="moz-txt-link-freetext">http://ehpes.com/n6mw/WireYagi2.pdf</a>).
Mine has a bit less duck tape. ;-)<br>
<br>
<br>
<o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">I tested only the driven element with
my nanoVNA, spot on 1.1 at my target of 50.2 (FT8). I
added the reflector - still 1.1. (All measurements taken
at about 10ft. elevation). I added the director - the
lowest SWR is now 2.5:1 at the same freq. (the SWR low
point did not change).<br>
<br>
<br>
<o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">The measured impedance dropped from
50.2 to around 30 after adding the director. I took the
wire off the director element support (aka PVC pipe) and
the SWR went back to 1.1:1. I did check that the
elements were parallel (as best as can be accomplished
with PVC tubing and bits of cutting board).<br>
<br>
<br>
<o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">What variables in the director
(length, spacing from DE, etc.) would cause this?<br>
<br>
73<br>
<br>
Tim - KC1RET<br>
<br>
<o:p></o:p></p>
</div>
</div>
</div>
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