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Wednesday, August 28, 2013

A 5/8 wavelength vertical for 10 meters. Post #224

How would you like to build a 10 meter vertical with some gain and a lower radiation angle than the usual quarterwave vertical?  You can realize this goal by building and using a 5/8 wavelength vertical antenna on the popular 10 meter amateur radio band.

If you use 50-ohm coaxial cable as your feed line, you'll need a matching device at the base of the antenna to make the antenna work correctly.  However, you can simplify the matching problem by using 450-ohm ladder line, a 4:1 balun, and a short piece of 50-ohm coaxial cable connected to the antenna terminal of your antenna transmatch.  The 5/8 wavelength vertical also requires a ground radial system to realize its full potential.  The radial system needn't be an extensive affair buried in the ground.  I used six elevated 5/8 wavelength radials for my antenna.  Thanks to the ladder line, the 5/8 wavelength vertical also is usable on 20 and 15 meters.

Faced with a more complicated construction project than the usual quarterwave vertical, why devote more time to build a 5/8 wavelength version of an already proven vertical design?

There are two reasons:

Gain.  Even at a level of 1 foot/0.30 meters above ground, the 5/8 wavelength vertical shows a 1.5 dB improvement over a dipole at the same height.  Properly constructed, the 5/8 wavelength vertical will show a gain of slightly more than 3dB over a dipole.

Lower angle of radiation.  According to some antenna experts, the 5/8 wavelength shows a low vertical angle of 16 degrees to the horizon.  Even a half-wave vertical antenna will exhibit a low vertical angle of at least 20 degrees to the horizon. Both antennas have better DX potential than a quarterwave vertical.

I built this highly modified 5/8 wavelength vertical antenna on Sunday, 26 August 2013, and was pleasantly surprised by its performance, considering the generally poor conditions on 10 meters.  I was able to get decent contacts on 15 and 20 meters as well.  Again, thanks to the ladder line, balun, and transmatch.

MATERIALS:

One 33 foot/10.06 meters  MFJ telescoping fiberglass mast.

One 5-foot/1.52 meters wood post to support the mast.

Six, 10-foot/3.04 meters pvc pipes and six, 3-foot/0.91 meters wooden stakes to support the pvc stakes. These posts would support the elevated radial system.  The radials would droop very slightly from the base of the antenna to the support stakes.

Six ceramic insulators to isolate the elevated radials from the support stakes.  One ceramic insulator was attached to the tip of the mast.  This insulator would support the vertical element of the antenna.

Sufficient #14 AWG housewire for the elevated radial system and the main radiating element.

One W9INN 4:1 balun, 50 feet/15.24 meters of 450-ohm ladder line, 25 feet/7.62 meters of RG-8X coaxial cable with UHF connectors, transceiver, dummy load, patch cords, low pass filter, antenna transmatch, and various tools.

ASSEMBLY:

The antenna was assembled on the ground.

Using the general formula for a 5/8 wavelength vertical antenna, 585/f (MHz)=L (ft)/178.308/f (MHz)=L (meters) and a chosen frequency of 28.4 MHz, I cut seven pieces of #14 AWG wire to a length of 20.59 feet/6.28 meters.  Six wires would be used for the elevated radial system.  One wire would be used for the main vertical element.  According to some antenna experts, the formula is about 2 feet/0.60 meters short of resonance.  So, you may want to cut your element lengths closer to 22 feet/6.70 meters.  I chose to leave the length at 20.59 feet/6.28 meters.

The vertical element was attached to the top ceramic insulator,which was secured to the tip of the mast with nylon ties and vinyl electrical tape.

The vertical wire was secured to the mast with nylon ties and run down to a point 12.41 feet/3.78 meters above the ground.

The six radial wires were attached to their pvc posts.

The 450-ohm feed line was attached to the base of the antenna (12.41 feet/3.78 meters above ground).  One wire of the feed line was soldered to the vertical element and the other wire of the feed line was soldered to the elevated radials coming from their support posts.  All connections were wrapped in several layers of vinyl plastic tape.

I hoisted the fiberglass mast onto its support stake, adjusted the elevated radials so they would be symetrical. and led the feed line, which was now about 12 feet/3.65 meters above ground level, to the garage wall where I had previously attached the W9INN 4:1 balun.  Twenty-five feet/7.62 meters of RG-8X coax with UHF connectors were attached to the balun.  The cable was led into the shack through a homemade patch panel in the shack window and then onto the Drake MN-4 antenna transmatch.  Small coax patch cords connected the Drake MN-4 to the Swan 100 MX transceiver, the dummy load, and the low pass filter.

INITIAL RESULTS:

As mentioned previously, there was a slight droop of the radials between the mast and the 10-foot/3.04 meters pvc support stakes.  The elevated radials were generally about 10-feet/3.04 meters above ground level.

With the help of the Drake MN-4, the W9INN 4:1 balun, and the 450-ohm feed line, I was able to get  a SWR of 1.3 to 1 on 20, 15, and 10 meters.  Tuning on 15 meters was a bit touchy.  Although I got some contacts on 10 meters (539 to 559 on Cw and 52 to 54 on SSB), the band was generally in poor condition at my Hawaii Island location.  Contacts on 20 and 15 meters were more consistent and stronger, with CW reports ranging from 569 to 599 and SSB results falling between 55 and 57 on 20 meters.  Fifteen meters picked up a bit by late afternoon with reports of 559 to 579 for CW and 55 to 57 for SSB.  The old Swan 100 MX was running around 25 watts.

I'll keep this antenna up for awhile and see what develops on 10 meters.

REFERENCES:

http://www.dx-antennas.com/5-8wavevertical.htm.

http://www.dxzone.com/dx20212/5-8-wave-vertical-antenna-calculator.html.

http://qsl.net/co8tw/vertical.htm.

Noll, Edward M.(W3FQJ).  "73 Vertical, Beam, and Triangle Antennas."  Editors and Engineers.  Seventh Printing. 1979.  Indianapolis, IN, 46268.

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Thanks for dropping by!

Aloha es 73 de Russ (KH6JRM).

BK29jx15--along the beautiful Hamakua Coastline of Hawaii Island.