'Smart' VHF tripod antenna for mobile missions

HF tripod antenna

[DESIGN DIMENSIONS AND MORE PHOTOS TO BE ADDED SHORTLY. MY APOLOGIES FOR THE DELAY, BUT WE ALSO HAVE A FULL TIME JOB TO KEEP OURSELVES GOING…]

This article demonstrates the construction of a VHF monopole over a tripod-like ground plane, based on the concept introduced on this post: “Special Tripod Antena…”

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As stated in previous post this antenna possesses several attractive characteristics:

 

  • Only 3 drill holes are required! (one for each radial). So you don’t spend much time with tools.
  • Cheap to construct, only 5 aluminium tubes (see text for details), a star supporter, 3 screws and a short PVC pipe are needed to make this antenna!
  • Portable and foldable: The antenna can be folded by simply unscrewing and then lifting up the elements.
  • Extremely quick to assemble and disassemble at any place and location.
  • Stable design. If you do it properly you can make a rock-solid design.
  • Light, easy to carry around.
  • Easy to install: just open up the radials and fix them down to the ground or any other surface or alternatively insert it on a vertical PVC pipe.
  • Vertical element tunable: The vertical element can be adjusted by shifting it up or down to fine tune the frequency.
  • Radials’ angle tunable: simply unscrew, adjust, screw again and you’re ready! This will help you adjust input resistance and match it to your conditions, in addition to the tuning of the vertical element!
  • No tools required for installation, operation or tuning. Everything is done by hand!
  • Ideal radiation pattern for omnidirectional coverage from all directions.
  • Small in size when packed. So you can enjoy it when you’re around on vocations and travelling.

Some friends have asked me to patent this design. I am against this idea as most patents end up being unused and instead of promoting a technology they restrict its use because of this. More advancements are achieved when more people participate on a open-hardware, instead of ‘locking’ something around the boring rules of the patent process. I speak from personal experience, as I have filled a patent in the past myself, but I realised that the cost of retaining its validity overtook the potential economic advantages that a simple patent might bring. So, I would rather share this here on my blog for people to use it freely and without restrictions. Do what ever you like with this antenna, to put it this way, it’s all yours!

This VHF antenna has worked successfully on all of my contacts. I’ve even managed to contact someone who was 125km away: Me with 5W and this antenna operating with a Yaesu 8900 from my car, the other side with 10W and a simple vertical antenna. Not bad I believe!

Don’t hesitate to email me for any questions/clarifications/improvements around this design through my contact form on this blog. Enjoy!

More photos:

Details of how to make the vertical element become tunable in simple steps: Please, not that these photos were taken when I was designing a tunable UHF dipole, so ignore the dimensions shown by the ruler. I am just showing the concept of how you can make an element with tunable characteristics. Cut your VHF elements accordingly and follow similar steps to achieve the result. In this case, I decided to use 2 aluminium tubes, one with 14mm diameter and another with 12mm diameter inserted one inside the other.

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