Step 1: Adjust the driven element length to center the SWR across your
desired bandwidth. I.E. adjust to make the SWR the same at the bottom and
top of your desired bandwidth.
Step 2: Adjust the harpin length to minimize the SWR at the midpoint
frequency of your desired bandwidth.
Step 3: Recheck the SWR across the desired bandwidth but it should be good
to go. Tweak if required.
Also be sure to note that the lengths in the BV204CA file are from the
centerline of the boom. The element bracket length in the BV204CA file is
2.95 whereas the actual bracket lengths are longer - so be sure to correct
your measurements relative to the centerline of the boom. Also, BV204CA
file shows DIR 1 at 157" which conflicts with the boom joining bracket.
Position needs to be shifted forward to clear the bracket which will change
the element length somewhat.
Hope this info helps & GL.
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Yuri
Sent: Friday, September 6, 2024 1:22 PM
To: towertalk@contesting.com
Subject: [TowerTalk] HyGain 204BA mod
Hello,
I recently modified my old 204BA using the BV204CA file (YW, Yagi for
Windows by N6BV) from the ARRL Antenna Book.
I moved Driven Element and Director 1, changed the element tip lengths where
necessary and changed Hairpin match length according calculations.
According to the computer model the calculated SWR is 1.09:1 on the resonant
frequency of 14175, and 1.40:1 on the edges: 14000 and 14350 at the 80'
height.
Hairpin spacing that used is 12 inches (different from the original one,
which was 6 inches).
In reality, I have SWR of 1.05:1 on 14090, which appears to be my new
resonant FREQ now, and 1.6:1 on 14000 with 2.6 on 14350.
Why is it so narrow?
What am I doing wrong? Should I use original hairpin rod spacing of 6"?
Old variant of this antenna was wider (better broadband) Any advise would be
greatly appreciated.
--
73, Yuri VE3DZ
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