Low Q Yagis - G4CQM - 2017

Segment Density...

The following assessment of two 144MHz yagi designs has been carried out using K6STI's Antenna Optimizer Professional version software. Screenshots of AOP results tell the story, both examples below converge at 22 segments per λ/2...

Until a software user is familiar with the segmentation necessary for various types of yagi models, it's important to test convergence by increasing segmentation density until results no longer change significantly. Note that in the two examples shown, convergence starts to occur with a lower segment density in the Low Q design!

When comparing 4nec2 and AOP, results will differ slightly. This is because AOP uses an enhanced version of the MININEC antenna-analysis program whilst 4nec2 uses NEC-2/4! The popular VE7BQH tables uses 25 segments per λ/2 with NEC software (EZNEC & 4nec2) for analysis.

Warning: Ham antenna designers regularly use 25 segments per λ/2 no matter what! This is dangerous when it comes to the higher bands (432MHz and up), particularly so if large element diameters are present. As an example >1/2 Inch (12.7mm) OD... AOP warns when segments shorter than the wire diameter are present. Under these circumstances segmentation has to be reduced until the warning goes... Failure to comply can give unreliable results!

segments shorter than the wire diameter are present

WAXX8S Low Q YagiPA819 High Q Yagi
WAXX8S Low Q YagiPA819 High Q Yagi
5 Segments per λ/25 Segments per λ/2
WAXX8S Low Q YagiPA819 High Q Yagi
10 Segments per λ/210 Segments per λ/2
WAXX8S Low Q YagiPA819 High Q Yagi
20 Segments per λ/220 Segments per λ/2
WAXX8S Low Q YagiPA819 High Q Yagi
22 Segments per λ/222 Segments per λ/2
WAXX8S Low Q YagiPA819 High Q Yagi
25 Segments per λ/225 Segments per λ/2
WAXX8S Low Q YagiPA819 High Q Yagi

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