Dave,
This is what I get running the numbers you provided for the modified tips
(all of them 53 inches and with 2.145 for the center of each element except
the driven element which is 1.25. Did you mean to increase the diameter of
the center section of the driven element also? This is for 14.000 - 14.350
every 50 khz.and the R set to 33 ohms.
32.41 -30.70 2.478 7.87 0 20.36 20.36
32.96 -27.66 2.261 7.88 0 21.93 21.93
33.42 -24.60 2.065 7.89 0 23.30 23.30
33.79 -21.49 1.884 7.91 0 24.17 24.17
34.07 -18.38 1.720 7.92 0 24.26 24.26
34.29 -15.23 1.569 7.94 0 23.64 23.64
34.44 -12.03 1.430 7.96 0 22.62 22.62
34.53 -8.77 1.301 7.99 0 21.46 21.46
This is the wire table:
Reflector
0.000 -3.125 50.000 0.000 3.125 50.000 2.145 3
0.000 -3.125 50.000 0.000 -45.000 50.000 1.250 11
0.000 3.125 50.000 0.000 45.000 50.000 1.250 11
0.000 -45.000 50.000 0.000 -91.000 50.000 1.125 13
0.000 45.000 50.000 0.000 91.000 50.000 1.125 13
0.000 -91.000 50.000 0.000 -141.500 50.000 0.875 13
0.000 91.000 50.000 0.000 141.500 50.000 0.875 13
0.000 -141.500 50.000 0.000 -165.500 50.000 0.625 7
0.000 141.500 50.000 0.000 165.500 50.000 0.625 7
0.000 -165.500 50.000 0.000 -218.500 50.000 0.438 13
0.000 165.500 50.000 0.000 218.500 50.000 0.438 13
Driven element
122.875 -30.000 50.000 122.875 30.000 50.000 1.250 15
122.875 -30.000 50.000 122.875 -76.000 50.000 1.125 13
122.875 30.000 50.000 122.875 76.000 50.000 1.125 13
122.875 -76.000 50.000 122.875 -126.500 50.000 0.875 13
122.875 76.000 50.000 122.875 126.500 50.000 0.875 13
122.875 -126.500 50.000 122.875 -150.500 50.000 0.625 7
122.875 126.500 50.000 122.875 150.500 50.000 0.625 7
122.875 -150.500 50.000 122.875 -203.000 50.000 0.438 13
122.875 150.500 50.000 122.875 203.000 50.000 0.438 13
D1
211.625 -3.125 50.000 211.625 3.125 50.000 2.145 3
211.625 -3.125 50.000 211.625 -21.500 50.000 1.250 5
211.625 3.125 50.000 211.625 21.500 50.000 1.250 5
211.625 -21.500 50.000 211.625 -67.500 50.000 1.125 13
211.625 21.500 50.000 211.625 67.500 50.000 1.125 13
211.625 -67.500 50.000 211.625 -118.000 50.000 0.875 13
211.625 67.500 50.000 211.625 118.000 50.000 0.875 13
211.625 -118.000 50.000 211.625 -132.000 50.000 0.625 5
211.625 118.000 50.000 211.625 132.000 50.000 0.625 5
211.625 -132.000 50.000 211.625 -185.000 50.000 0.438 13
211.625 132.000 50.000 211.625 185.000 50.000 0.438 13
D2
307.250 -3.125 50.000 307.250 3.125 50.000 2.145 3
307.250 -3.125 50.000 307.250 -17.250 50.000 1.250 5
307.250 3.125 50.000 307.250 17.250 50.000 1.250 5
307.250 -17.250 50.000 307.250 -63.250 50.000 1.125 13
307.250 17.250 50.000 307.250 63.250 50.000 1.125 13
307.250 -63.250 50.000 307.250 -113.750 50.000 0.875 13
307.250 63.250 50.000 307.250 113.750 50.000 0.875 13
307.250 -113.750 50.000 307.250 -137.750 50.000 0.625 7
307.250 113.750 50.000 307.250 137.750 50.000 0.625 7
307.250 -137.750 50.000 307.250 -180.750 50.000 0.438 11
307.250 137.750 50.000 307.250 180.750 50.000 0.438 11
If I change the driven element to have the tip length of he DE at 56.625
and leave everything else the same I get
34.97 -12.03 1.429 7.87 0 19.96 19.96
35.58 -8.92 1.310 7.88 0 21.47 21.47
36.09 -5.80 1.210 7.89 0 22.80 22.80
36.51 -2.63 1.134 7.91 0 23.71 23.71
36.83 0.55 1.117 7.92 0 23.93 23.93
37.08 3.78 1.172 7.94 0 23.48 23.48
37.26 7.06 1.264 7.96 0 22.58 22.58
37.38 10.40 1.377 7.99 0 21.51 21.51
I think there is definitely an adjustment to compensate for the capacitance
between the element and the plate for the driven element, increasing the
length?
If I leave the 56.125 for DE tip and change all elements to have the center
section at 1.25" diameter I get
35.11 -12.14 1.434 7.87 0 20.53 20.53
35.69 -9.04 1.315 7.88 0 22.01 22.01
36.16 -5.92 1.214 7.89 0 23.22 23.22
36.54 -2.75 1.138 7.90 0 23.90 23.90
36.84 0.44 1.117 7.92 0 23.86 23.86
37.06 3.68 1.169 7.94 0 23.21 23.21
37.22 6.97 1.261 7.96 0 22.21 22.21
37.31 10.33 1.374 7.99 0 21.11 21.11
In all cases the R was set to 33 ohms. This was all done with AutoEZ and
200 segments per wavelength. If I run the setup for the last table above
using NEC2 instead of NEC4 I get
33.99 -18.00 1.702 7.73 0 18.04 18.04
34.83 -14.81 1.547 7.74 0 19.57 19.57
35.56 -11.64 1.414 7.74 0 21.05 21.05
36.18 -8.48 1.299 7.74 0 22.33 22.33
36.69 -5.31 1.204 7.75 0 23.18 23.18
37.10 -2.12 1.141 7.76 0 23.40 23.40
37.42 1.11 1.139 7.77 0 22.99 22.99
37.67 4.38 1.199 7.78 0 22.18 22.18
The difference between NEC-4 and NEC-2 is significant in terms of SWR. In
the case of the numbers from NEC-4, I am happy. In the case of NEC-2, not
so much. Some of these SS amplifiers do not like 1.7-1.
This is a lot to look at and I may be doing something wrong. I would
certainly like to learn from it if so, but what I "think" I can definitely
say is that for a 20m Yagi the increased diameter in the center for a
Hygain clamp makes close to absolutely no difference.
Back to setting up the station on Cayman Brac for Multi-Multi instead of
staring at the computer :-).
Thanks & 73...Stan, K5GO/ZF9CW
On Wed, Nov 5, 2025 at 2:37 PM Stan Stockton <wa5rtg@gmail.com> wrote:
> Dave,
>
> Thanks.
>
> Was I correct in my assumptions outlined in second paragraph of my last
> message regarding lengths to use for the larger equivalent diameter?
>
> Stan
>
> Sent from my iPhone
>
> > On Nov 5, 2025, at 2:14 PM, Leeson <leeson@earthlink.net> wrote:
> >
> > Here's the model from the 1990s that I've used in YO for the 204BA,
> with the tip dimensions for CW:
> >
> > Hy-Gain 204BA
> > 14.000 14.175 14.350 MHz
> > 4 elements, inches
> >
> > 2.1448 1.2500 1.1250 0.8750 0.6250 0.4375
> > 0.0000 3.1250 41.8750 46.0000 50.5000 24.0000 53.0000
> > 122.8750 0.0000 30.5000 46.0000 50.5000 24.0000 53.0000
> > 211.6250 3.1250 18.3750 46.0000 50.5000 24.0000 53.0000
> > 307.2500 3.1250 14.1250 46.0000 50.5000 24.0000 53.0000
> >
> > Match: 2 0.2500 8.0000 18.0000 4.0000 26.5 50.0
> > Bracket: 1 3.2500 7.2500 2.0000 0.2500
> >
> > I used a modified set of tip dimensions that improved the SWR bandwidth
> over the whole band without much gain or F/B penalty:
> >
> > Phone CW Mod.
> > Refl 50" 53" 53"
> > Driven 50" 53" 50.75"
> > Dir 1 51" 53" 49.5"
> > Dir 2 51" 53" 49.5"
> >
> > Other dimensions including Beta match are as standard per the manual.
> The gain, F/B and SWR comparison YO calculation is as follows:
> >
> > MHz 14.0 14.175 14.35
> > 204BA Gain 8.18 8.33 8.49
> > F/B 23.6 22.3 16.8
> > SWR 1.3 1.3 2.2
> >
> > 204BA Mod Gain 7.98 8.08 8.20
> > F/B 19.7 26.0 21.0
> > SWR 1.5 1.0 1.5
> >
> > As part of design efforts for my home setup, our former HC8 M/M station
> and others, I've played around with many modifications of the basic 204BA
> elements, including direct feed with closer first director for wide SWR
> bandwidth. For construction convenience, I've tried to change only the
> first director location, leaving the rest of the elements in the original
> positions. Modern modeling software can produce useful designs.
> >
> > One last thing I've looked into more recently is the tip adjustment
> necessary to account for the effect of wire lead length from a balun to the
> driven element. In the case of direct feed, I've found that the tip
> dimension as calculated needs to be reduced by a factor of 1.5-1.7x the
> lead length, rather than the 1:1 I had expected. I use a wider frequency
> range to help with the broadbanding calculations.
> >
> > Here's an example of that process, using 1/2" tips:
> >
> > Hy-Gain 204BA 50 Ohm
> > 13.950 14.175 14.400 MHz
> > 4 elements, inches
> >
> > 0.0510 2.1450 1.2500 1.1250 0.8750 0.6250 0.5000
> > 0.0000 0.0000 3.1250 41.8750 46.0000 50.5000 21.5000 56.5000
> > 122.8750 5.0000 0.0000 30.5000 46.0000 50.5000 21.5000 58.5000
> > 162.5000 0.0000 3.1250 24.8750 46.0000 50.5000 21.5000 58.0000
> > 307.2500 0.0000 3.1250 18.3750 46.0000 50.5000 21.5000 54.1250
> >
> > Match: 1 0.0000 0.0000 0.0000 0.0000 26.5 50.0
> > Bracket: 1 3.2500 7.2500 2.0000 0.2500
> >
> > MHz 14.0 14.175 14.35
> > 204BA 50 Gain 8.15 8.29 8.41
> > F/B 25.5 21.0 17.5
> > SWR 1.04 1.03 1.03
> >
> > The Hy-Gain 204BA seems still to be the standard of comparison in short
> monobanders for 20m. Some folks have suggested extending the boom, but
> making the 204BA longer runs you into the weird behavior of antennas that
> are near 1/2 wave boom length (you either get gain or F/B, but not both).
> This happens for 20m boom lengths from 30-36 feet. It takes a 40' boom to
> begin to get clear of the near-half-wave boom area, and 42' to 45' to have
> real design freedom.
> >
> > For my location here on a ridge, our high winds dictate strengthening
> elements per the techniques outlined in my Yagi book. One caution is not to
> allow any holes near the inner end of reinforcing tubes, as this can be a
> site of eventual fatigue failures. Caribbean experience supports the HyGain
> technique of ropes inside element tips.
> >
> > Hope this is useful. As my grandkids always note, "Grampa, TMI!"
> >
> > Dave, W6NL/HC8L
> >
> >
> >> On 11/5/25 5:19 AM, Stan Stockton wrote:
> >> Thanks, Dave! I had forgotten all about the great book you wrote 30+
> >> years ago. Also, my wife and I are watching a series on TV that we
> >> watched 10 years ago and it's almost like we had never watched
> >> it.😀
> >> So in the chart it shows the equivalent diameter as 2.14" and the
> >> length as 2.925". I am assuming from what I read that the half
> >> length of the clam shell clamp that extends out from the edge of the
> >> boom is 2-5/8" with an overall length of 7.25" (5.25" + 2") and that
> >> the length of 2.925 is derived by adding .3" for half the electrical
> >> length of the boom diameter? Hope that makes sense and is correct?
> >> Thank you so much for reminding me of the book. A lot of it is way
> >> over my head but it's full of practical information as well.
> >> 73...Stan, K5GO/ZF9CW
> >> On Wed, Nov 5, 2025 at 12:52 AM Leeson <leeson@earthlink.net <mailto:
> leeson@earthlink.net>> wrote:
> >> Modeling of the HyGain element clamp is derived in Chapter 9 of my
> >> 1992 book, "Physical Design of Yagi Antennas,"
> https://www.dropbox.com/s/hmhkeofz0igrg1e/Physical%20Design%20Of%20Yagi%20Antennas%20D%20B%20Leeson%20V2.pdf?dl=0
> >> <
> https://www.dropbox.com/s/hmhkeofz0igrg1e/Physical%20Design%20Of%20Yagi%20Antennas%20D%20B%20Leeson%20V2.pdf?dl=0
> >
> >>
> >> From page 9.3, the equivalent diameter of the HG204BA clamp is 2.14
> inches. This clamp model is used in K6STI's YO and other Yagi
> >> software.
> >> Dave, W6NL/HC8L
>
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