Minimal Reactance Antenna

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Minimal Reactance Antenna

Postby wb4ene » 13 Jan 2005, 23:36

Ken WB4ENE -
This is a revolutionary new antenna. I call it the MRA (Minimal Reactance Antenna). It gets its name from the network analyzer plot from 1.6 - 30 Mhz. The reactance curve crosses the real line only once, at 6.89 MHz, where this 8ft tall antenna is resonant. The antenna works on 160m through 10m. It is a top-loaded monopole. I don't think there has EVER been a top-loaded monopole with as much top-loaded capacitance as this MRA. Its mast is a 6 inch cylinder pipe, 6 feet long, that is surrounded by the 6 foot diameter octagonal group of panels of aluminum sheet. The metal conductivity is optimum and every scrap of efficiency is gotten from how it is put together.

I match the antenna with a remote LC network made by John Bliss. The "trampoline" base is 18 feet in diameter and is connected to the shield side of the feed-line through the tuner. Only 15 uH of inductance is needed to make a 50 ohm match.

The design is scalable, from 250 feet (for 40kHz submarine broadcast) to nanometer arrays etched on silicon wafers. A beer-can + pie-pan can be used for a 2 meter version.

Long radials are not required. I have NO radials.

On the recent 160 meter contest I worked 265 contacts; 40 US states and 14 countries in 12 hours. If you would like a schedule to hear the antenna, contact me at wb4ene @ bellsouth net (delete spaces, add .)
http://ken.crawley.org
qrz.com WB4ENE

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Last edited by wb4ene on 01 Mar 2005, 21:19, edited 7 times in total.
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Minimal Reactance Antenna?

Postby rusty » 13 Jan 2005, 23:54

Very interesting!

However, I am curious about the 'Minimal Reactance Antenna' name. I would expect considerable reactance change with frequency. Is there some reason that doesn't happen?

How long have you used it? What do you know about the performance?

Rusty
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Postby Guest » 14 Jan 2005, 00:31

Rusty,
I am currently on 75m in the DX window... breaking pileups.
The original reason for the minimal reactance name long since passed, but when you look at the network analyzer plot of the antenna from 1.6 - 30 MHz, you see an absolutely smooth semi-circle plot, with self-resonance at 6.89MHz, 5 ohms real, and no reactance. So, think of the Minimal part as that there is no particular frequency range where the reactance does not wander around. It looks like a piece of feed-line.

Ken WB4ENE.
You can contact me on AOL IM KenCrawleySC. I'm in Saint George, South Carolina.
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Top open or loaded?

Postby jlong » 14 Jan 2005, 07:27

Ken,

Is the top of the six foot center mast open or loaded by one or more capacitors connected to the top of the octagonal panels?

jlong
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Feed line

Postby rusty » 14 Jan 2005, 13:55

Is the coax feed line burried? If not, how high and long is it?

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Postby wb4ene » 15 Jan 2005, 14:19

75 feet of coax goes from the antenna to the shack. The coax is laying on the ground. Moving the coax around does not affect the impedance plot on the network analyzer, nor does connecting wires to the antenna tuner ground. This implies the antenna is not being tuned by nearby conductive objects. There are no discrete capacitors connected to the antenna.

I will be replacing the feed-line in March with a new lightning cloaking technology called LRC (lightning retardant cable) that will be applied on the top of heliax. This technology will make it not necessary to bury the feed-line. http://www.lrccable.com http://www.cabletraxinc.com

Ken Wb4ene
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Plots of the MRA

Postby wb4ene » 01 Mar 2005, 21:05

I wonder if the horizontal wires that I attached to my MRA (minimal reactance antenna) could be considered a Windom, because they are not the same length. Here is the VSWR plot:

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