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Author Topic: J-Pole antenna design  (Read 1461 times)
KV9U
Member

Posts: 166




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« on: October 11, 2006, 03:16:03 PM »

I have been making a few types of J-Pole half wave verticals, mostly from twin lead and 450 ohm open wire which seemed to work the best for me and was easier to work with due to the wide spacing.

Has anyone ever actually compared the standard J-Pole design to the Slim Jim version of the J? I know that theoretically some (e.g., W4RNL), have suggested that the Slim Jim might actually have slightly lower gain based upon modeling.

Considering that it is usually more work to build and tune a Slim Jim is there anyone who has found a true benefit?

Also, N0IMW's Arrow Antenna Company has a J design which appears exceptionally well made and avoids the issue of finding the 50 ohm point on the matching section. He uses both matching rods for both 2 meters and 440.

Has anyone physically compared this design to a conventional J and found any difference?

Has anyone ever physically compared the 5/4 wave J that  was designed to directly connect to coax? This antenna is likely to have high angle radiation.

http://www.rason.org/Projects/ant54/ant54.htm

73,

Rick, KV9U
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N8CUI
Member

Posts: 18




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« Reply #1 on: October 13, 2006, 10:46:17 AM »

Rick,

I can only offer my perceptions on these designs.

I own a 300 ohm twinlead rollup J Pole, a 450 ohm twinlead J pole encased in PVC, the Arrow antenna, and the RASON 5/4 wave antenna. I live in northeast Ohio on a slight hill. I prefer a flatter radiation angle that a 1/2 wave antenna offers to that of 1/4 wave.

I rarely use 440 so all of my experience with these antennas are on 2 meters.

The RASON 5/4 wave was built as described on their website. It is mounted about 15 feet above the ground next to my deck. I can best describe the pattern as fragmented and unpredictable. Some lobes can really reach out, though. I rarely use it. Antenna articles say not to exceed 1/2 or 5/8 waves lengths. I recall not being able to hit a repeater 10 miles away at one time. SWR was great and it is an open-stub design that the ARRL antenna book described as better for unbalanced feedline.

The two twin lead 1/2 wave J poles work fine for me, although the rollup usually hangs too close to walls, etc. and probably couples with the surroundings. The 450 ohm antenna in PVC is a trooper and goes with me into the field. I made it from the July 1995 QST article "Build a Weatherproof PVC J-Pole Antenna" by Dennis Blanchard, K1YPP. I can push it up 15 feet on a mast and easily hit repeaters 20 miles away using 25 watts. I am certain these antennas perform no different than what most operators experience with them. They are cheap and effective. The downside is the time and patience necessary to get them tuned.

The Arrow J pole antenna design is just plain awesome. I have mine mounted over the garage at about 25 feet. It has been up over 5 years and has gone through 55 mph gusts, ice storms, and heavy hail. It is still standing straight as the day I put it up. The only sign of age is the red plastic caps have faded into white. I use 45 watts and hit repeaters several counties away. There is a graphic at the Arrow website that shows the radiation pattern. I can believe it based on my own experience.

My order of preference of 1/2 wave 2 meter antennas is 1. Arrow J pole, 2. 450 ohm twin lead J pole, 3. 300 ohm twin lead j pole, and last, the 5/4 wave RASON antenna. I have other 1/2 wave antennas that would fit in here, too. But none would surpass the Arrow antenna.

I am curious about what you may find on the Slim Jim design. Internet searches seem to indicate it is more popular in Europe than in North America.

73
N8CUI - Jim
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