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Hi-VHF 5-El Yagi Optimized by K6STI
K6STI's Hi-VHF 5-Element Yagi with Rearward Swept Driver Element analyzed using 4nec2.
4nec2 files are included in *.doc format, providing all dimensions.  Save as *.txt format then rename as *.nec.
4nec2 files can also be imported into EZNEC and other antenna simulation programs.

Brian Beezley, K6STI, used his AO 8.06 Antenna Optimizer to find a configuration that minimized response to the rear.
On 19Jun he replaced Original with slightly revised RevA, which has improved SWR and Gain:
http://www.ham-radio.com/k6sti/vhftv.htm
K6STI's Optimized Yagi design is only 31.4-inches long and 32.4-inches wide, but provides good coverage across all Hi-VHF
channels (Ch7-13) with excellent Front-to-Rear (F/R) and Front-to-Back (F/B) Ratios and moderate (7.4-9.3 dBi) Net Gain.
Although slightly longer, performance differences between versions are very small, mostly reflecting fine tuning.

In 4nec2 analyzes, F/R is the ratio of gain towards the front (azimuth = 90-deg) to gain towards the rear (azimuth = 180-deg).
And F/B is ratio of gain exactly towards the front to gain towards the rear with an included angle of (my choice) +/- 45-deg.
This is different than the worst side-lobe level calculated by K6STI.  Note that 4nec2 calculated SWR is slightly higher than K6STI's.

I also investigated a Folded Dipole variant which has a Characteristic Impedance of 300 ohms (vice 75-ohm for above).
After optimizing Folded Dipole Element separation, SWR was further reduced to under 1.4 with up to 0.25 dB more gain on
Ch13 than K6STI's Yagi RevA, with small increase in F/R and F/B (except Ch12-13 decreased some).  [Further optimization is possible.]

DIYers can consider whether the small mis-match loss of a 1:1 Coax Balun (or direct connect) is smaller (or greater)
than the small (0.5 dB) loss in Hi-VHF band for a low-loss 4:1 Balun, as discussed HERE:
http://www.avsforum.com/avs-vb/showthread.php?p=15851345
http://www.ham-radio.com/k6sti/balun.htm
http://homepage.mac.com/kenwetzel/Low_Loss_Balun.htm

Gain, F/B and F/R are compared to 4-El K7MEM Yagis (only 2-3 channels), 8-El K7MEM Yagis (only 3 channels),
as well as fol. full band antennas: 14-Element ZS6BTE LPDA, 14-El Wedge Zig-Zag LPA and 14-El Stacked Zig-Zag LPA.

All of the 8-El and 14-El antennas are much longer (about 100 inches), with higher gain.

An open challenge is to design a compact HIGH GAIN Hi-VHF antenna with FULL-BAND coverage....

EDIT (20Jun2009 @ 08:10am): Updated charts to reflect comparison of RevA to Original.

EDIT (19Sep2010): Added FORWARD Gain and SWR (75-ohm) charts for UHF Band...although it might pick up strong signals,
it does NOT provide good performance in the UHF Band.
Date(s): June 20, 2009. Album by holl_ands. 1 - 29 of 29 Total. 16021 Visits.
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Hi-VHF 5-El K6STI Yagi with Swept Back Driver
RevA - 3D View

Red circle at center of swept element identifies
a short "simulated SOURCE wire".


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Hi-VHF 5-El K6STI Yagi RevA - Top View
[One small box = 0.5 inch]

Click on image to see hi-rez.


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Hi-VHF 5-El K6STI Yagi RevA - Side View

[One small box = 0.5 inch]

Click on image to see hi-rez.


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Hi-VHF 5-El K6STI Yagi - Compare Raw & Net Gains

Top: Folded Dipole (300-ohm) variant.
Middle: RevA K6STI design.
Bottom: Original K6STI design.
For All: Gain = 7.5 to 8.5 (+/- 0.25) dB


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Hi-VHF 5-El K6STI Yagi - Compare SWR

Note K6STI's calculated SWR was lower than 4nec2,
but still showed increase on Ch13


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Hi-VHF 5-El K6STI Yagi - Compare F/R and F/B Ratios
Excellent suppression of signals coming from the rear.

"Rear" is very narrow angle towards the rear.
"Back" includes response +/- 45-deg from "Rear".


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Compare 5-El K6STI Yagi RevA to 4-El K7MEM Yagis

K7MEM (DL6WU equations) provides higher gain
but only for two adjacent channels.


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Net Gain Comparison:
8-El K7MEM Yagis (Ch8-10 and Ch11-13)
14-El ZS6BTE LPDA (Log Periodic Dipole Array)
14-El Wedge Zig-Zag LPA (Log Periodic Array)
14-El Stacked Zig-Zag LPA (Log Periodic Array)
5-El K6STI Yagi RevA


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F/R and F/B Ratio Comparison:
14-El ZS6BTE LPDA (Log Periodic Dipole Array)
5-El K6STI Yagi RevA
8-El K7MEM Yagis (Ch8-10 and Ch11-13)


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Hi-VHF 5-El K6STI Yagi - Original
Gain, F/R & F/B


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Hi-VHF 5-El K6STI Yagi - Original
SWR


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Hi-VHF 5-El K6STI Yagi - Original
Impedance


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Hi-VHF 5-El K6STI Yagi RevA - Gain, F/R & F/B

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Hi-VHF 5-El K6STI Yagi RevA - SWR

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Hi-VHF 5-El K6STI Yagi RevA - Impedance

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Hi-VHF 5-El Swept Folded Dipole Yagi
Segmentation and Colorized Horizontal Gain Pattern.


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Hi-VHF 5-El Swept Folded Dipole Yagi
3D View


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Hi-VHF 5-El Swept Folded Dipole Yagi
Top View
[1 small box = 0.5 inch]


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Hi-VHF 5-El Swept Folded Yagi - Gain, F/R & F/B

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Hi-VHF 5-El Swept Folded Yagi - SWR

Note Characteristic Impedance = 300-ohm
[K6STI Swept Driver Yagis above are 75-ohm]


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Hi-VHF 5-El Swept Folded Yagi - Impedance

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Hi-VHF 5-El Swept Folded Yagi - Front View

[1 small box = 0.5 inch]


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Hi-VHF 5-El Swept Folded Yagi - Side View

[1 small box = 0.5 inch]


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Hi-VHF 5-El K6STI Yagi RevA - AvgGainTest = 1.0
Verifies 4nec2 results are accurate.


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DOC25
Hi-VHF 5-El K6STI Swept Driver Yagi - Original
[Characteristic Impedance = 75-ohm]

4nec2 file - download, save as *.txt
then rename as *.nec


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DOC26
Hi-VHF 5-El K6STI Yagi RevA: Better SWR & Gain
[Characteristic Impedance = 75-ohm]

4nec2 file - download, save as *.txt
then rename as *.nec


Enlarge Microsoft Word Document 27
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DOC27
Hi-VHF 5-El Swept Folded Dipole Yagi Variant.
[Characteristic Impedance = 300-ohm]

4nec2 file - download, save as *.txt
then rename as *.nec


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Hi-VHF 5-El K6STI Yagi RevA - UHF FORWARD Gain

Very poor on lowest and highest UHF channels.


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Hi-VHF 5-El K6STI Yagi RevA - UHF SWR (75-ohm)

EXCESSIVE, except for a narrow range of channels.


 
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BestEloise | https://CleverJerry.blogspot.com, Tue, 10 Sep 2019 2:18AM
Thanks for all the info.  My nearest HDTV stations are about 90Kms due north and I'm looking for a way to "cut the cable"!!
 - 
Gregory Andracke, Mon, 18 Aug 2014 7:43AM
Nice resource of ideas
 - 
Damon Hill, Sat, 29 Sep 2012 7:58PM