5
$\begingroup$

I am building the antenna for the first time and I have choosen to start with 40m inverted-v. I am almost done with the center insulator made of PVC piping elements, three eye hooks and SO 239 connector at the bottom.

Now I am getting ready to measure and attach legs and I have a bit of a question here.

I found an online calculator and according to it, for 40m Inverted-V with 22 degrees angle from horizontal, each leg should be around 31ft 10inch. Now I am trying to figure is that the distance between the eye hook on center insulator and end insulator or that is the total length of wire that should be used. I am working on the theory that I will need around 10 inches of wire to tie it to both ends so if I were to use the exact length of wire, the distance between the center point and end insulator would be a bit shorter?

Is my dipole leg length the actual length of wire used or the distance between the center point and end insulator.

$\endgroup$
  • $\begingroup$ Thanks a bunch for all the answers. Can anyone recommend balun? I know that there are 4:1 and 1:1 but I am not sure which one should I be using. I will use about 50ft of RG8X coax. Also, I was thinking about building balun myself but then I watched a few video tutorials and it seems like a big project for me at this time. if you know of some simpler solution please share it with me. $\endgroup$ – Bogdan YU2DBC Apr 19 at 4:16
  • $\begingroup$ Hello Bogdan, Unlike a typical chat-style forum site, our goal is to create a database of high-quality answers to questions. Unfortunately, this does not answer the question at the top. However, you are most welcome to ask your question in a new post here, as explained in the Tour and Help sections. I have moved your question to a comment for now. $\endgroup$ – Mike Waters Apr 19 at 16:16
  • 1
    $\begingroup$ Hi Mike. I was in doubt and I was not sure if I should comment or even open a new thread. Thank you for explaining it to me and moving my answer to the comments. $\endgroup$ – Bogdan YU2DBC Apr 20 at 16:46
  • $\begingroup$ Sorry, I meant your question, not answer. Yes, you probably should ask this in a new question. Before you do, try searching for balun and see if there is already a thread that answers your balun question. $\endgroup$ – Mike Waters Apr 20 at 16:59
  • 1
    $\begingroup$ I will do so :) $\endgroup$ – Bogdan YU2DBC Apr 20 at 17:10
5
$\begingroup$

If I were making an antenna like that, I would add the extra 10" (25cm) first anyway, because when you come to tune it it's much easier to trim the wire than it is to add wire to it later.

Also, because the antenna is an inverted V (a kind of dipole - a balanced antenna) and you are using coaxial cable to feed it, you should consider using a balun at the feedpoint. This will effectively stop the outside of the coax from carrying unwanted (common-mode) currents and being part of the antenna, and will help keep RF out of the shack.

EDIT: To answer the question, it is my understanding that it's basically the length of the wire between the centre and the tip of each leg, and any additional wire you use to tie it off or to wrap around an anchor does not count in the length calculation.

$\endgroup$
3
$\begingroup$

The length is measured between the center and the end insulator.

I'd further add: don't overthink it. Common practice is to cut the wire a bit long, then iteratively make it shorter until you get a good match at your target frequency. Things like proximity to ground or other conductive objects can cause some deviation from the idealized conditions used by generic calculators, so an iterative empirical approach is often best.

$\endgroup$
1
$\begingroup$

The formula for calculating the end-to-end length of a half-wavelength center-fed dipole is

  • in feet: 468÷f
  • in meters: 143÷f

where f=frequency in MHz. That is measured "from loop to loop"; that is, after the extra wire you allow for the wire loops inside the end insulators is twisted back on itself and soldered.

Between the center of the center insulator to each end is 1/2 of this dimension, the "leg" as you asked.

Using that has always got me very close to resonance, if not right on. However, as others have stated, you may want to leave extra. But I never have.

$\endgroup$
  • 1
    $\begingroup$ There are 3.28 feet in a meter, 468 / 3.28 = 143. $\endgroup$ – Phil Frost - W8II Apr 18 at 18:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.