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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:

February 24, 2018 22:50

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