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Building a 2 and 6 Meter Coaxial Yagi
Using the velocity factor of coaxial cable to reduce the size!

by Daniel Weismann W6HJ

These Yagi antenna projects are based on ideas and projects by
K4MMG, STEVE and N0KHQ, JOHN
(See references at end of article)

Reduce the size of your 2 and 6 meter Yagi antennas
by using these simple and effective ideas!

 

Steve, k4mmg asked me to share my design of two coaxial Yagi antennas I made for use on 6 and 2 meters. Steve's design included using pvc pipe for his 2 element, 6 meter beam, and his 3 element, two meter beam. John's design, a 17 meter Moxon, was built and tested with good results using this same technique.

I changed the design somewhat from Steve's design, in that I used 1.5" square, fiberglass tubing, with 3/16" fiberglass rod for element support instead of the pvc pipe method; having some concerns about strength in high winds, and am, in general, a lousy plumber. I also made the 6 meter yagi a 3 element, and the 2 meter, a 4 element.
I cemented the elements with good-grade, long setting, two-part epoxy. Follow the instructions for best results.

I secured the coax onto the element support fiberglass rod with wire ties, then used heat shrink tubing to cover it all. All ends were sealed with epoxy resin, then silicon for good measure and then painted the entire antenna with good exterior spray enamel. I tuned the antennas with my antenna analyzer to the low end of the band where I do most of my work.

I calculated the lengths from the formulas given in the articles mentioned above:

234/your frequency x (.66 for RG58 ) or the velocity factor of your coax = 1/2 of dipole...  but added an inch to the length before trying to see the resonant frequency with the analyzer. It is easier to subtract length than add it. (If you only have an swr meter, then just use the formula above and tune as needed).

Drawings NOT to scale!


6 Meter 3 Element Yagi

Active Element (coax) and spacing lengths for 6 meter version: (low end of band)
Looking from left to right in drawing above.

Reflector = 59 inches
Driven     = 56 inches
Director   = 54.32 inches
Spacing   - Reflector to driven 31.25 inches
                  Driven to director   24.75 inches
Total boom length = 56.50 inches

Support length for coax elements as needed in your construction. Your final lengths for elements may be slightly different due to your construction. Tune as needed for lowest swr.



2 Meter 4 Element Yagi

Active Element (coax) and spacing lengths for 2 meter version: (low end of band)
Looking from left to right in drawing above.

Reflector   = 24.75 inches
Driven       = 23.50 inches
Director 1  = 23.75 inches
Director 2  = 22.02 inches

Spacing   - Reflector to driven  = 17.25 inches
                  Driven to director 1 =  13.25 inches
                  Director 1 to end director = 10.20 inches
Total boom length = 42.00 inches

Support length for coax elements as needed in your construction. Your final lengths for elements may be slightly different due to your construction. Tune as needed for lowest swr.



Coax feed connection detail



Up in the air! 2 meter Yagi on top, 6 meter Yagi on bottom.

At this time, I have not done any formal and organized readings with other folks on the frequencies, but find their performance - great!

Both antennas are supported on a 1 1/2" OD tubing, supported on a framework on my house, and turned easily by an old Radio Shack TV rotator.
I would also recommend the addition of ferrite chokes on the coax at the feed point and possibly one on the radio end of the feed line.
Radio Shack Catalog #'s 273-105 or 273-069. Use the one that will fit your coax.

They work great, are very broad banded and am very satisfied with their performance.

Daniel Weismann email earlgreywdj at gmail.com

(Do not use the QRZ.com address. It is not working)

W6HJ
References:
K4MMG 2 and 6 Meter Antennas
N0KHQ 17 Meter Moxon

Disclaimer From the Editor: All information on this page represents the author's opinion, experiences or results, based on his background, or experience with the particular subject in good faith. This does not imply that the provided information has been substantiated by actual theory if needed, depending on the article content, and in no way intended to discredit actual theory. It should only be regarded as an outlet for him to publish his desire to share his thoughts, experience, methods, results, performance, or his ideas with you for your information if you choose to use it for reference. This and other articles referenced on this page should be considered experimental!




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