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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