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2 element 6 meter beam

Jul 21st 2012, 12:12

KD2AAG

Joined: Sep 28th 2010, 15:05
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Total Posts: 0
hello everyone i am wanting to build a 2 element 6 meter beam, the thing is i am going to use 2inch pvc for the boom i have all the tubing for the radials but every construction plans show use of metal boom . i realize that the pvc i not the ideal matterial, now if the antenna works the way i want i will make a better more rigid antenna. my question is with the boom not being conductive will this affected the the antenna performance thank you 73s kd2aag
Sep 18th 2012, 09:56

W8ARR

Joined: Apr 4th 1998, 00:00
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This is a good article for what you are looking for
http://www.hamuniverse.com/K4mmg2and6meter.html

73 W8ARR
Sep 18th 2012, 17:23

W1VT

Joined: Apr 4th 1998, 00:00
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Aug 1982 - QST (Pg. 34)
Go For The Gain, NBS Style
Author: Lusis, Dennis, W1LJ
http://p1k.arrl.org/pubs_archive/75186

This article describes how the boom correction factor is calculated.
A metal boom requires longer elements to compensate--you could calculate the correction factor and appropriately shorten the elements.

Alternately, I'd suggest, for 6M antennas, to shorten the element lengths by 60% of the metal boom diameter.

Zack Lau W1VT
ARRL Senior Lab Engineer


Jan 21st 2013, 22:46

K5TEN

Joined: Nov 11th 2010, 21:20
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I noticed in that 1982 QST article that the authoir used a 180 degree phasing harness. I have been looking into homebrewing a couple of yagis for 6m and 2m and noticed that some of the plans called for 50 ohm coax direct feed...no balun, phasing harness, gamma feed or even hairpin matching. I also am finding it hard to find baluns for VHF. Is it that VHF antennas no longer need baluns or special matching? While I live on a mountain and all the neighbors have CATV I still do not need RFI/TVI problems. What am I missing? Am I trying to build VHF antennas with an HF mentality?
Jan 22nd 2013, 02:31

W1VT

Joined: Apr 4th 1998, 00:00
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Total Posts: 0

A very simple feed that doesn't use a balun fashions the element into a J, so that you can attach the shield to a low impedance point--the center of the longer element. Not as good as having a balun, but when you are trying to design homebrew antennas that can be built in 3rd world countries, simpler is better.

But, if you try to direct feed a Yagi, splitting the element and running the shield to one side and the center conductor to the other side, you have the outside of the shield providing a convenient path for RF back to he radio. Worst case, you end up with something that looks more like a tri-pole feed than a dipole feed.

Zack Lau W1VT
ARRL Senior Engineer
Jan 27th 2013, 01:13

K5TEN

Joined: Nov 11th 2010, 21:20
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Thank you Mr Lau!

Then riddle me this: I am (finally) finding VHF current baluns for my project but now am wondering if a matching section AND balun are both required? I am starting to get my head wraped around the gamma match concept but need to know if BOTH are required? Can a 75 Ohm 1/4 wave coax matching stub suffice? (In addition to a 1:1 current balun?) Thank you!!
Jan 27th 2013, 12:43

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

It depends. You only need a matching section if the impedance is other than 50 ohms--it is certainly possible to design a Yagi for 50ohms impedance, though this often isn't done because it usually means sacrificing something else. Similarly, a balun is often omitted with J and Gamma feeds because the feed itself provides the balanced to unbalanced conversion. A good design provides a good performance to cost ratio--best isn't a good choice if you can't afford it.

Zack Lau W1VT
ARRL Senior Lab Engineer

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