433MHz Half-wave dipole for LRS

How to make a simple half-wave dipole useful for 433MHz LRS.

You need:

  • SMA Pigtail with your desired coax length, the cable I used is RG316
  • Plastic antenna tube (found some made by Reely here in Germany, 380mm long)
  • Two pieces of wire each 200mm long, I used AWG28
  • Hotglue

Required parts

Mark the center on the antenna tube and use a solder iron to make a small hole in the tube right at the center. Do not cut the tube in half, this will give a better mechanical stability.
Prepare the open end of the SMA pigtail. Keep the feedpoint cap as short as possible.

Prepare open end and antenna tube

Solder the two pieces of wire to the coax open end. Be sure the center wire will not touch the outer shielding.

Soldered wires

Pull the wires through the antenna tube and the coax open end into the tube hole.
Then apply some good amount of hotglue to strengthen this point.

Dipole feedpointDipoleFeedpoint fix

Cut the antenna tube including the wires inside to an overall length of 300mm. Each half of the tube to 150mm.

Overall length 300mmEach half 150mmReturn loss

On my EZ* I sticked the dipole through the wing. On the lower end, the antenna tube (and only the tube!) was cut and put back together using silicon fuel tube (from nitro engines). This way it´s flexible and will not break in case of ground contact during landing.

Dipole on Easystar wing

28 thoughts on “433MHz Half-wave dipole for LRS

  1. Hello Michaels..
    i like your projects very much.
    I have an pair of openLRS but not have the antennas. I will make first test with your design.

    BTW, do you know where i can find a conventional design for a transmitter antenna ?

  2. Hi Michael. Thanks for posting your designs. About the lenght of 433 antenna, I was curious as to why the lenght is 15 cm. Are you calculationg a velocity factor of 0.88?

    Untill I found your page, I was more in the range of 0.95. Your Rohde & Schwartz prooves me all the way wrong I guess?

    At last is there a way to calculate this factor?

    Thanks a lot,

    • The plastic tubes used to stabilize the antenna wires have an influence on the velocity factor, hence on the length of the wires.

  3. Question! if i were to use piano wire instead of just regular wire and just put heat shrink over it would you say that combination would probably be best at your same lengths or otherwise? also for this freq. the tx and rx antennas dnt have to match as long as they are both matching in polarization correct? (ie. monopole or inverted V on the tx and a dipole on the rx)

    • Piano wire and heat shrink will work, but due to different dielectric constants the length maybe differ. But I think the effect is negligible.

      Antenna types on both ends of the link don´t have to much as long as the polarization equals.

  4. Thanks for sharing your knowledge!

    If I configure the rx-tx system to work on 435Mhz, what is the better lenght of wire? Can you give us the formula to calculate the lenght wire?


  5. Hello,

    Great post here.
    You mentioned “SMA Pigtail with your desired coax length, the cable I used is RG316”

    So what should be the desired length ? It does not matter at all reception-wise ? Or does it ?

    Thank you

  6. Hi. If someone needs a decent antenna but don´t need 11KM of range and has limited space (20x20cm aircraft xD) can you suggest an alternative?

  7. great info Michael, tell me… what antenna did you use in the transmitter for the 11kms endurance, did you use one like this as well ? thanks

  8. Hi Michael,

    I came across your project when trying to make a 445mhz antenna for my openLRS. Could you tell me the measurements for 445? I don´t have a fancy SWR meter – wish I did though! Thanks.

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