Make a simple whip antenna for 5.8Ghz- linear polorized FPV video

It’s always been advised to use circular polarized antenna for FPV, such as skew planar (four-leaf) or cloverleaf antenna (three-leaf). Although they do allow better range and reception, there are situations where you are better off using simple linear polarized antenna.

Linear polarized antenna can be made very small and light weight, especially useful for weight-critical application, such as on a micro quadcopter.

It’s funny everybody talks about how to make CP antenna, theory how the length are calculated etc, but rarely mention the basic 5.8Gghz video transmission antenna like whip or dipole. Hope I I got this right here and actually help someone who wants to DIY this. I am using this antenna on my DIY 5.8Ghz FPV combo with good result.

What’s inside a whip antenna

If you open a whip antenna that comes with every 5.8Ghz video transmitter or receiver, you will find it’s just a simple Coaxial Cable inside.

linear-polarized-antenna-5.8ghz-dipole-fpv-inside-length

dipole-antenna-inside-fpv-video-transmitter-5-8ghz

But what we really need to know is, the length of the exposed wire affects the signal frequency that it receives. If the wire is 12.92mm then it’s tuned for 5.8Ghz, but only a little shorter e.g. 12.70mm, and it’s now tuned to 5.9Ghz.

For example this one is not very well made for 5.8Ghz, could be a little longer. For 2.4Ghz system, it’s the same such as radio receiver.

dipole-antenna-fpv-video-transmitter-length-5-8ghz

Calculation of wire length for antenna

If the antenna is a quarter wave monopole antenna, then its length should be a quarter of the signal wavelength.

Length (m) = c / frequency / 4

Where c is the speed of light.

The more precise wire length is, the better signal you should get ideally. If you are using Coaxial Cable, it doesn’t matter how long the shell is, all that matter is the exposed wire (the part that is without the shielding). Alternatively if you are using a wire like copper wire, just cut it to the calculated length.

tx5823-5-8ghz-200mw-video-transmitter-antenna-wire-cable

Further reading: 5.8Ghz Frequency Bands For different FPV brands.

16 thoughts on “Make a simple whip antenna for 5.8Ghz- linear polorized FPV video

  1. Jimmy

    hello.
    I fly on 5733 mhz . Speedof light is 299792458 m/s .
    299792458/5733/4= 13.073,105616605
    my wire length is 13.073 mm ??

    Reply
  2. Kirk

    Hey Oscar !!!

    Thanks for this I love the simplicity of the single copper antenna on my whoop. Yesterday I broke my vx1100 cloverleaf and cut one of the leafs down to 12.92mm and soldered it back on to the center pin of where the other one was and voila !!! reception… cant really tell but I think its better than before. don’t really expect much from the 10mw cam but it works well enough for cruzin’ around the house and I didn’t have to buy another !!!

    is 12.92 the magic number for 5.8 or is there another resource I should refer to as I fall down this rabbit hole ???

    Thanks again and Cheers !!!

    ~Kirk

    Reply
  3. Jos G.

    The Taranis and the others you mentioned are for 2.4Ghz. Oscar’s blog post is right on the money for a 5.8ghz antenna. The picture shown is a sleeved dipole not a regular dipole. The sleeved dipole has a ground plance “bullet” of the same length as the exposed wire. I’ve had really good results with a basic dipole – exposed wire around 12.9mm length. The speed of signal is slower in the wire than in the air hence the very small discrepancy in the calculated 1/4 wavelength and the length of the wire.

    So to recap – 2.4Ghz uses a long wire for 1/4 wavelength based on the frequency calculation.
    For 5.8Ghz video the exposed wire length = ~12.9mm

    Reply
  4. Michael Nørgaard

    The simple cobber antenna in your picture. What lenght is that. I find it hard to understand the way you explain “bare” wire lenght og a whip antenna. There is no bare exept at the very bottom where antenna ond two negative wires stick out. The simple splutioon with jus one cobber cable seems more easy and if it works as godd I’ll use it. Building a H8 mikro indoor surprise for the son. Like this one: youtube.com/watch?v=DREHnDY1WVk

    Reply
    1. Oscar Post author

      Please search for “length” in the article you will find the number. “bare” is basically the exposed wire without shielding.

      Reply
  5. David

    The bullet shaped piece is not plastic, it’s metal and serves as a counterpoise. It and the exposed center conductor together make a dipole antenna.

    Reply
  6. Pilotgeek

    The antenna is shorter on some due to the velocity factor of the coax cable. 11.71 is likely correct when tuned to match the cable.

    Reply
  7. Albert

    If I search the web for 5.8 linear antenna length I get very different results. You saying here the correct length should be 12.92 mm. On rcgroups some folks are saying 2.3 and 2.7mm. wtf? So what is the right length?

    Reply
    1. Oscar Post author

      everywhere I have seen suggests around 13mm, and I have been using that in my DIY antenna and getting decent results..
      if you measure any existing commercial antenna you should also they use this length…
      lastly, i would really appreciate it if you could join the forum: http://intoFPV.com … I don’t want to miss your comment, because I only check my blog comments only once a week, but I use the forum daily!

      Reply
  8. Casper

    I guess it’s better to calculate the wavelangth as ”Length (m) = (c / frequency ) / (4 x 0.93)”
    The velocity of electricity in copper will effect the lengt of the antenna.

    (Sry for my english)

    Reply
    1. FAERRY

      i’ve been searching everywhere for this! wouldn’t that make it slightly shorter? i’m trying to figure out why the taranis and other 3rd party replacement antennas i’ve bought are around 32.5mm instead of 31.2mm?

      Reply

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