FlightAware Discussions

DIY Vertical Halfwave

I have been using a 440-900 Mhz antenna from my Handheld radio. Worked but not getting a lot of tracks. I made a home made vertical half wave antenna and hung it in my porch window facing south.
Much better ! now to move it out doors and see if it gets more tracks and longer distance.

Link https://youtu.be/ViodMxV77eM


Half-wave antennas need to be fed from the middle. For the setup like in the picture, more appropriate is quarter wave.

The dipole leg goes down on the other side :stuck_out_tongue:

Anyhow … those legs look far too long for 1090 MHz.

For 1090 Mhz, the two legs put togather should be about 13.6 cm (5.3 inches), i.e.about the size of a hand

My 1090 Mhz 1/2 Wavelength Dipole With Satellite in-line Amplifier.

Click on image to see larger size
Click again to see full size


Oh dear.

Half wave dipole antennae do not need to be centre fed.

It is very common to feed a haflwave dipole antenna from the end.

It is frequently used in a ground independent vertical antenna for both base station and mobile use.

It is a high impedance unbalanced feed.

There have been numerous thread here about J-pole antenna which is an end fed halfwave.


If you feed a 1/2 wave long wire from an end, then it is a 1/2 wave monopole whip, not a dipole. If you have provided a ground plane also, then it is still a half wave monopole, but acts like a full wave dipole.

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I don’t want to just edit my post so take out the word dipole and therefore remove the discussion about dipoles and monopoles as it is irrelevant.

I will simply restate

I also mentioned a ground independent antenna which implied that there was no ground plane.

i.e. an half wave radiating element in free space.

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Could you please clarify this.
Do you mean:

  • a 1/2 wave - long wire
  • a 1/2 wave long - wire

Yes it’s a half wave.


By “a 1/2 wave long wire”, I mean:
A wire whose length is 1/2 wavelength

On mobile use, the ground connection is done mostly trough human body capacitance.

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Well in my haste to make my antenna I used CM instead of MM. I have now cut the elements to the correct length.


For what frequency?
At 1090 Mhz half wave is only 5.3 inches / 13.8 cm, while you antena in the video seems much longer than this.