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The Three L-Antennas

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ANTENTOP- 01- 2017, # 021

The Three L-Antennas

 

 

If a second horizontal arm is added at 180 opposite and both are tuned by length to the desired frequency, the radiation field balances. The radiation pattern becomes circular and the antenna becomes a tall ground plane vertical.

The MFJ-1790 10 meter antenna (Reference 7) is an example. It has an 11-foot vertical and two 6-foot radials to give Low Radiation Angle for outstanding DX.

 

 

 

 

Figure 5

Tall L-Dipole

 

 

The Wide L-Antenna

 When the vertical arm is short, the length of a 90 side arm can be adjusted to resonate the antenna to the desired frequency. The SWR match can be better than the Equal-L Antenna. Depending on elevation, ground and diameter of the wires or tubes used, there will some ratio between the length of the vertical and horizontal arms that will give a nearly perfect match to a 50 ohm coaxial cable.

 This Wide-L configuration has the characteristic of being shorter than a halfwave dipole with nearly the same gain.

 

Having both horizontal and vertical polarization, it is less effected by undulations in DX skip reflections (QSB) than a conventional dipole.

  Antenna modeling software can optimize a vertical dipole for the best wide OFC ratio at 1/2-wavelength feedpoint elevation over ground. Using that capability, Figure 6 below shows what happens with a 2/3-1/3 ratio as the longer lower arm is swung upwards in 15 increments.

 Note that the best SWR and Gain combination occurs at around 105, or 15 above horizontal.

This compares favorably with the gain of a center-fed dipole using the same wire and fed at the same elevation over the same ground.

 

 

 

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Last Updated:

March 23, 2017 23:05

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