[TowerTalk] Adding 15 meters to a 204BA

Wed Nov 5 14:37:35 EST 2025

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 at 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 at earthlink.net <mailto:leeson at 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