Free! Excel Worksheet for Building Any 1/2 Wave Dipole (Center-Fed, OCF, Windom, New Carolina Windom)

Here is a spreadsheet I designed in Microsoft Excel for calculating the first cut and the final cut (after testing) of a 1/2 wave dipole, whether center-fed, classic off-center-fed, Windom, or New Carolina Windom. If you use it for a plain ol’ center-fed dipole, just ignore the references to “long leg” and “short leg” — the numbers will still be right. Anyhow, you’re welcome to use it, pass it around, whatever:

DipoleWorksheet.xls (Microsoft Excel)

I’d enjoy hearing from any of you who end up using this spreadsheet to build an antenna!

If you find any bugs in this spreadsheet, please let me know. Note that it is protected for your convenience, but you can unprotect it anytime you like to see the formulas in each cell (there is no password).



Filed under Antennas, New Carolina Windom

11 responses to “Free! Excel Worksheet for Building Any 1/2 Wave Dipole (Center-Fed, OCF, Windom, New Carolina Windom)

  1. Bill Taylor

    LibreOffice 3.3 opens it just fine using Calac. Much faster than Microsoft sir. thank you very much for the program. I have to modify my antenna and rehang it soon so this will help me out greatly

  2. Todd Mitchell

    Dear Bill,

    You’re welcome!

    This really came in handy for me when I made my final adjustment to the New Carolina Windom yesterday afternoon. It turns out that I didn’t have quite enough spare wire up there to lengthen it perfectly, so I had to use the option at the bottom of the spreadsheet for arbitrary adjustments.

    Once I figured out how much spare wire I had to work with on the long leg, I called down to my son and he punched in the figure for an arbitrary adjustment to that leg. Then he called up to me and told me how much to remove from the short leg. That sure beat trying to do algebra while sitting on the peak of a steep roof — and eliminated the chance that I would make an irreversible mistake in the process. (By the way, even though I came up a few inches short it still works great!)

    I’d enjoy hearing back from you after you use the spreadsheet for your antenna. Let me know how it works for you!



  3. Pingback: Free! Excel Worksheet for Building Any 1/2 Wave Dipole (Center-Fed, OCF, Windom, New Carolina Windom) | Elmering « Ad5vj's Blog

  4. Chad

    I realize that this is somewhat an older posting here. I love the calculator xls this is a huge helper for me! Thank you so much. Do you happen to know where I can find information on building a Balun to go with such a build assuming I will be feeding with 50ohm coax?

    • Todd Mitchell

      You’re welcome, Chad. The answer depends upon what kind of antenna are you building and what kind of feedline are you using. For instance, are you building a center-fed dipole, off-center-fed dipole, or New Carolina Windom? Are you feeding it with coax or ladder-line?

      For my New Carolina Windom I built a 4:1 voltage balun. (Read about it here.) But for most antennas you would use a current balun, not a voltage balun. After reading my article on baluns, let me know if you have any questions and I’ll try to answer them if I can.

      Thanks for dropping by!


      Todd, NØIP

  5. Chad

    In the selection process of your balun how do you determine which type of balun to use 1:1 or 4:1 voltage or current. What I have is an RCI-2950 that was converted to the Chicken Band and after putting it back to a 10m radio and a little tuning I am going to use it while camping for my 10m rig. Using your XLS file I was able to determine the length of the wire needed for the 10m band here is what I came up with: 10.25 x 6.23 long and short legs respectively. Then feeding the entire setup with 100′ of RG-8X. I would have thought from my reading on the internet I would need a 4:1 current using the OCF Dipole.

    You talk about the “New Carolina Windom” and the “Windom” what is the difference between the two? As far as I can see there was only instructions for 3 different dipoles in your calculator. Windom, OFC and Center Fed is there another calculation point the for “New Carolina Windom”?

    I will be sure to follow all your posts from now on! Thank you…

    • Todd Mitchell

      Yes, you would use a 4:1 current balun when feeding an OCF Dipole with 50 ohm RG-8X. But if I were cutting an antenna just for 10 meters I would go with a center-fed dipole, myself. The advantage of an OCF dipole is that it gives you multi-band performance — it works on the band you’re cutting it for, and for some bands above it as well. Since 10 meters is already the top HF band, this isn’t an advantage for you. That’s why I would use a center-fed dipole in your situation. But if you’re already cut your antenna as an OCF dipole, no sweat — it should still work well for you.

      There are really two main questions to answer when choosing a balun — what your balun’s ratio should be, and whether it should be a voltage or a current balun.

      First, the question about ratio. Whether you choose 1:1, 4:1, or some other ratio depends on the impedance of the antenna at the feedpoint and the impedance of your feedline. If the impedance of the antenna at the feedpoint is four times the impedance of the feedline, e.g. 200 ohms vs. 50 ohm RG-8X, then you would use a 4:1 balun. If on the other hand the impedance of the antenna at the feedpoint is the same as the impedance of the feedline, e.g. 50 ohms vs. 50 ohm RG-8X, then you would use a 1:1 balun — if choose to use a balun at all in that instance.

      Now, the question about current vs. voltage baluns. The design of the antenna dictates which balun (voltage or current) to use. If you want to choke off as much common-mode current as possible from running down the feedline, then you want to use a current balun. This is usually the case (like with your OCF Dipole). If on the other hand you want to deliberately let that RF stand on your feedline, then you would use a voltage balun, since it isn’t as effective as the current balun in choking off common-mode current. This is not normally desirable, but in the case of the New Carolina Windom (which is really the same as a Carolina Windom, but since that name is trademarked some of us call the homebrewed version the “New” Carolina Windom) you do let a section of the feedline radiate below the feedpoint — and then you add an RF choke at the point where you want it to stop radiating. If you want to read more of what I’ve written about this antenna, go to the right-hand side of this blog and select “New Carolina Windom” from the drop-down box called “Categories.”

      The biggest differences between the Windom and the New Carolina Windom are 1) the original Windom had a single-wire feedline, not a coax 2) the single-wire feedline of the Windom carried common-mode current all the way back to the shack (unless you put a choke on it somewhere), whereas the New Carolina Windom is more precise in designating a portion of the coaxial feedline to carry common-mode current. By the way, here’s a good discussion you may enjoy.

      In my spreadsheet I suggest a proportion of .378 for the Windom (including the New Carolina Windom) and .333 for an OCFD (Off-Center-Fed-Dipole). However, there is debate over which proportion is best for either of these types of antennas.

      • Chad

        Your information is very thorough and I appreciate you and your willingness to help me out. Not a lot of folks that are willing to go the extra mile like you did in your explanations. I think I actually have a nice grasp on the concept of using Baluns and the ideas behind different dipole antennas now. Your explanations, further reading on the internet etc. no one has explained it quite like you did and it really brought it all together for me. So thank you for that!!

        I will report back with the findings on my build as soon as I finish up. Thanks again and 73’s…

      • Todd Mitchell

        You are quite welcome, Chad. I am glad to be of some help to you. I look forward to hearing how your antenna project goes.


        Todd, NØIP

  6. Rick

    Hi Tod
    I just built an OCFD to add to my collection of wire. I got a decent SWR when I first hung it but I wanted a lil more information on tuning this fine antenna.
    What a pleasant surprise it was to find your spreadsheet !!
    Thank You, Thank You, Thank You

  7. Fantastic! Great for us math challenged. Use it to do all my Windom OCF antennas. Second cut is almost perfect.

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