Thursday, November 9, 2023

Sand in my shoes

How wonderful it is to get sand in my shoes putting up vertical antennas on the beach of a salt-water shoreline.




That's where I was lately testing the VDA (Vertical Dipole Array) antennas I made for Rob N7QT just prior to his departure for the Solomon Islands (H44) this week.

The job (the ask) was to help Rob out with fabrication of two VDA that were designed to operate DX-style on a salt-water shoreline at H44.    The VDA concept is ideal for this application -- Low take-off angle, utilize the salt-water nearby to replace the typical ground-plane and use a Director element (or Reflector if needs want).  But most likely, the setup with these VDA on H44 will be Driven element to a Director.

The gain differential is awesome for these VDA.  8-9 dB gain in the direction of choice.  That's amazing.

Making these antennas though was a challenge because the material I needed wasn't readily available in the local Seattle area and it required some hard-core work to just figure out how to get the parts to work.  Had there been time I could have ordered the right sized (wall thickness) to make all of the sections slide as-is into each other (making the job easier and faster).. But I had to do a bit of machine work at the lathe to get the 15 meter VDA to integrate per the design.

The 10 meter VDA utilized some spare aluminum I got from Rob N7QT which luckily had the right wall-thickness to make the telescoping effect much easier to achieve without a lot of machine work.

The insulators between top/lower half of the elements was specifically chosen Delrin (Acetal Round Rod Delrin Homopolymer) -- which is both easy to machine and strong as you wouldn't believe.  Even down to narrow diameters, the Delrin should stand up to the battle against the elements/wind on Solomon Islands.  I made extra parts just in case there is a problem.

These antennas were the first generation version.   We're going to revise things -- improve things and after H44 we will collect data about their operation and use that knowledge to improve the design for the next batch.

In short -- if you need a DX antenna for your operation, you might consider these.   20 meters through 10 meters and there is even a route to making a 6 meter version, but that is still on the drawing board.   VDA's like these have a special application -- near the beach, near salt-water.   Ping me if you want one.

The box was checked:  "Sand in my shoes putting up vertical antennas near salt-water for a DX'p"   Maybe not a full check since we weren't on an island, but a bit closer to that goal now!

Here's the fun we had testing out the VDA's for 15 meters and 10 meters.   Looking forward to working H44 once they arrive and are activated.

(L to R:  Justin "Jay" K5EM, Robert "Rob" N7QT and Jeff W7BRS)



(Photo credit: Justin, K5EM)




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