G4CQM 50Ω Direct Feed Low Q Low Noise Yagis


Dipoles Explored...

Split DipoleFolded DipoleLFA LoopV Split Dipole
Split DipoleFolded DipoleLFA LoopV Split Dipole

Updated 22-02-2018... G4CQM's Dipoles Explored blows a hole wide open in myths propagated on the Internet concerning the pros and cons of particular driven elements!

To create a level playing field the following analysis has been carried out in K6STI's Antenna Optimizer Professional (AOP) version software. AOP is perfect for analysis of loops and bent elements! Each dipole has been tuned for minimum reactance at 144MHz. Segmentation has been set at 25 segments per λ/2 in all examples. The Split Dipole, Folded Dipole and LFA Loop all exhibit their own respective intrinsic impedance...

Meanwhile the V Split Dipole can easily be adjusted to 50Ω by simply changing the swept back angle and tuning out reactance by altering length!

Note that the LFA Loop and V Split Dipole exhibit some pattern distortion (not symmetrical) which has an impact on the final overall pattern when located in a yagi build, LFA Loop being worst of all!

Integration and the working of each of these different dipole types into a yagi build is complex. Mutual coupling occuring between elements and subsequent loading effects will impact on resultant intrinsic feed impedance in a positive or negative way! This is dependent on the tuning regime of all the parasitic elements along with the driven element which also determine the polar pattern in both E & H planes, and over the desired operational bandwidth.

Radio Amateurs may be seduced by marketing speak into the benefits of a particular system. However, the reality is that all of the different feed systems are in one way or another a compromise, no one system is perfect, so don't be taken in by boastful claims!

At the end of the day it may well come down to ease of construction!

Also see:


Split Dipole

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Split Dipole
Split Dipole

 

Split Dipole in AOPAntenna File - Symbolic Dimensions
Split Dipole in AOPAntenna File - Symbolic Dimensions
AzimuthElevation
AzimuthElevation

 

Split Dipole - Average Q-factor = 4.9
Average Q-factor

 

Split Dipole - SWR
SWR

 


Folded Dipole

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Folded Dipole
Folded Dipole

 

Folded Dipole in AOPAntenna File - Symbolic Dimensions
Folded Dipole in AOPAntenna File - Symbolic Dimensions
AzimuthElevation
AzimuthElevation

 

Folded Dipole - Average Q-factor = 3.2
Average Q-factor

 

Folded Dipole - SWR
SWR

 


LFA Loop

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LFA Loop
LFA Loop

 

LFA Loop in AOPAntenna File - Symbolic Dimensions
LFA Loop in AOPAntenna File - Symbolic Dimensions
AzimuthElevation
AzimuthElevation

 

LFA Loop - Average Q-factor = 2.5
Average Q-factor

 

LFA Loop - SWR
SWR

 


V Split Dipole

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V Split Dipole
V Split Dipole

 

V Split Dipole in AOPAntenna File - Symbolic Dimensions
LFA Loop in AOPAntenna File - Symbolic Dimensions
AzimuthElevation
AzimuthElevation

 

V Split Dipole - Average Q-factor = 7.1
Average Q-factor

 

V Split Dipole - SWR
SWR

 



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