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

James

Half-wave antennas need to be fed from the middle. For the setup like in the picture, more appropriate is quarter wave.
https://www.tutorialspoint.com/antenna_theory/antenna_theory_half_wave_dipole.htm

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

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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.

S.

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.

James

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.

James

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.