T2FD Calculator

I love a good T2FD antenna and have built a good few. There’s a few variations but they all work well and are easy to construct. I’ve been asked a few time about the length and spacing so I made a small Excel sheet to work it all out and provide data for the 3 most popular variations.

Free free to download and use. The sheet is protected to prevent the formulas from getting messed up but if you would like to experiment with alternative formulas then please just contact me for the password. All I require is for my original credit to remain on any derivative works.

M0LMK T2FD Calculator

15 Replies to “T2FD Calculator”

  1. When I click on Frequency, I get a message,
    “Protected Cells cannot be modified”
    What do I do to make that work.
    I’m using OpenOffice.

  2. Hi Mike. I don’t know if it will work in Open Office. I use Excel. If you send me an email via my contact form then I’ll send you an unprotected sheet over to see if that works.

  3. I tried to ask from your comments page but somehow it didn’t send. Could you kindly send me a password for the file?

  4. The contact form should be fixed. Please try sending me a message again or email me direct matt@.co.uk and I’ll send a copy over to you.

  5. Hi Mike, thanks for your work, I’ve often wished for a T2FD calculator.
    Maybe I’m missing something but there’s nothing appearing (other than a row of Xs )under the ‘Feeding’ section; no info about the resistor or the impedance transformer.

  6. This is what it should say:

    Modern: Feed in the centre on the bottom with 50 Ohm coax to a 16:1 BalUn (you can also try a 16:1 UnUn with a 1:1 BalUn after if you can’t find or build a good 16: BalUn).Use a 820 Ohm non inductive resistor rated to at least 1/3 of your total power (I prefer to use a rating of at least 1/2 on the shorter 1/2 wave model) in the centre at the top.

    Traditional: Feed in the centre with 300 Ohm twin feed (any length). Terminate the twin feed in a 4:1 BalUn and run 50 Ohm coax to the radio. Use a 300 Ohm non inductive resistor rated to at least 1/3 of your total power (I prefer to use a rating of at least 1/2 on the shorter 1/2 wave model) in the centre at the top.

    I hope that helps.


  7. First of all, thank you for this, I’m starting a build on the 1/3 wave now. I have a pre-built 1/4 wave T2FD already up and I’m pleased with the performance, but you know, always reaching for more. My intention is strictly for only shortwave listening, using an SDR radio. I have a little challenge in that I have nothing to support the center, so I need what is airborne to be as light as possible. So, I am going with the traditional type with ladder line to a balun on a post where the ladder line would drop down. That said, I have some questions:

    1. 300 ohm ladder line seems to be only available as copper-clad rather than solid copper wire. I’m reading copper clad has more loss than solid copper wire. For a 20 foot drop, is this even an issue?

    2. On the balun, 4:1 voltage baluns are readily available, but 4:1 current baluns are hard to find. Do you have a preference for an SWL application?

    3. It seems to me like the antenna is presenting 300 ohms impedance, and a 4:1 balun converts it to 75 ohm. This makes me wonder if I would be better off using 75 ohm coax to the radio, but then again, the radio has a 50 ohm antenna port. The coax run will be about 25 feet. So, I am thinking about using 75 ohm coax instead, mainly due to cost, if the difference is negligible. Any thoughts on this?

    4. I can do this as a flat-top or a sloper, and not to get into too much detail, but as a flat-top I could have it at about 20′ height. As a sloper, I could make the higher end around 30′. All other things, time, effort material being equal, which would you go for sheer receiving performance?

    I appreciate your time, and I know these are a lot of questions. If you want to email me back, that would be fine too.

    Thank you so much!

    ~Phil KD0SCJ

  8. Hi Phil.

    I’m always happy to help where I can. I don’t consider myself a T2FD expert but I have probably built more than your average Ham and I have used them in commercial settings. Here are my thoughts for your application:

    1. I suggest that the difference in loss between solid and copper clad on HF with a 20′ run would be negligible. I would use whatever you can get easily.
    2. A current BalUn is the best option but you can work around it. They are pretty simple to build and I would look for the 4:1 Guanella style. You can use a 4:1 voltage BalUn and then add a 1:1 choke right next to it (Element wires -> 4:1 Voltage UnUn -> 1:1 Choke -> Coax to radio). It’s not ideal but it will do the job.
    3. For RX only, take 75 Ohm coax back to the radio and don’t worry about the small mismatch. You won’t notice any performance loss.
    4. I would always suggest going for the tilted, sloper configuration. It will offer better omnidirectional performance that a “flat top”.

    Come back and let us know how your experimenting goes!


  9. I’m back! Here is the final configuration, at least for this year:

    1/3 wave size with default measurements from the spreadsheet, and traditional style feed to minimize airborne weight and wind profile. Hoisted North/South with heights of 30 feet and 8 feet respectively to form a sloper. 300 Ohm twinfeed to a MFJ DXE-LLSP surge/static protector, then a 4:1 current balun, and finally, a 60 foot run of 75 Ohm coax to an RSPdx SDR radio.

    As I was building this, I received an MFJ-1886 ADF loop antenna, which is one of the better loops available for SWL, but pricey at $320 USD. The RSPdx SDR has multiple antenna ports, so it is easy to compare the T2FD to a modern ADF loop.

    Results: The T2FD and the Loop have very similar performance, and I do go back and forth between the two for the better reception. The T2FD brings higher signal levels with only a slightly higher noise floor. In some cases, there is just a lot more noise on the bands due to lightning or a nearby power transmission line and both do a good job with noise rejection.

    The Loop, which is only rated to 30MHz does indeed start to fall off at higher frequencies, where the T2FD just keeps going strong, all the way up into our public service frequencies around 860MHz, almost equaling a discone VHF/UHF antenna built just for those frequencies.

    It’s really hard to find a fault overall with the T2FD, it performs, it is economical, and easy to build. It seems to be the prefect antenna for those with enough room to put one up.

    I have very early plans for next year, to beef the T2FD up to transmitting standards and use it as my first HAM radio transmitting antenna.

    Matt – Thank you for this website, the calculator and your comments, they were key to my success.

    ~Phil, KD0SCJ

  10. Excellent work, thanks.
    I’ve been kicking around the idea of a T2FD for a while, but the space availiable is just a bit tight – this calc shows I can get it done.
    I had this working in Libre Office, but kept getting a pop-up which eventually just wouldn’t go away, regarding “exporting not allowed for one element of this document”, so it’s likely a glitch with LO compared to MS.
    Looks like I need a password or an unprotected version, if you could be so kind.

  11. Hi Dave. I’ll see if I can find the original and email it over. PLease share your Libre Office version with me once you have it working so I can update this page with it.

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