Tuesday, January 31, 2017

5/8 Wave Vertical Antenna Calculator. Post #1029.

5/8 Wave Vertical Antenna Calculator
Accessed on 01 February 2017, 04:50 hrs, UTC.
Author:  W4SAT.
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You can design, build, and operate your own 5.8 wavelength vertical antenna by using this simple javascript antenna calculator. An antenna matching device, such a wire-wound coil, must be added between the vertical antenna element and the coaxial cable feedline so that the antenna can match the impedance of the coax feedline.  The addition of 3 to 4 quarter wavelength radials will make the antenna more efficient and easier to adjust.

As you can guess, the 5/8 wave antenna is a bit more complex to build than the simple ground plane antenna using a 1/4 wavelength vertical element.  So, why go to all the trouble of building the 5/8 wavelength vertical antenna?  W4SAT gives us several reasons to build this larger vertical antenna:

"So why would anyone use a 5/8 wave antenna if they have to go through all that extra work? After all, a ground plane antenna provides a nicer match. There are a couple of answers. The first is GAIN. The computer shows that the antenna (mounted 1 foot above ground) has a gain of about 1.5 dBd higher than a dipole's gain (also mounted 1 foot above ground.) 

The second reason you may want to use the 5/8 wave vertical is to obtain a lower angle of radiation. A half wave antenna's radiation peak angle is 20 degrees. You'll find that the 5/8 wave antenna's angle of radiation is just 16 degrees making it an even better dx antenna."

Supportable 5/8 wavelength wire antennas can be built for any amateur radio band, but using this antenna on bands between 20 meters and 70 cm seems to be the most practical from a standpoint of space and materials.

In this post, an experimental 5/8 wavelength wire antenna was built using a chosen frequency of 28.5 MHz, with the vertical element measuring 22.5 feet/6.85 meters.

To use the 5/8 wavelength formula, just plug in your chosen frequency and select meters or feet as your preferred measurement.  The formula is based on the common expression of 585/f (feet)/178.307/f (meters)=length.

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