Author Topic: Inpedance matching for Collapsible Yagis (for field use)  (Read 4901 times)

Offline Greekman

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Inpedance matching for Collapsible Yagis (for field use)
« on: November 20, 2015, 09:02:42 AM »
hi all!
I am moving slooooowly forward with a VHF Yagi antenna that it will be able to be diassambled and stored within half its boom.
I have sorted out all issues but the impedance match one.

I consider using DK7ZB 4-element Yagi design and one of his impedance chokes
http://www.qsl.net/dk7zb/dk7zb-match.htm
scroll down half way where you can see this pic.

Questions.
1- will this choke work?
2- boom outside diameter is 1and1/4 inch. I rather have it inside the beam if applicable
3- anything else I am missing?

Offline armymars

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #1 on: November 20, 2015, 06:01:39 PM »
  I use to have a friend who use to match J Poles with a telescoping hair pin match. This aloud him to match his antenna for it's environment and frequency. He moved around the plant a lot and what steel was around him made a differences.

Offline Carl

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #2 on: November 20, 2015, 07:49:16 PM »
The HAIRPIN MATCH is by far easier to use as done with this antenna....

http://w8jxn.com/files/Download/2m_df_antenna.pdf

Offline Greekman

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #3 on: November 21, 2015, 02:21:31 AM »
thanks...

But here comes another question.
Assuming I cut the elements to design specs and the hairpin match too.
And i see aconsiderable SWR on my meter. How do i know it is the match or the elements that are out of spec?

Offline Carl

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #4 on: November 21, 2015, 06:09:20 AM »
thanks...

But here comes another question.
Assuming I cut the elements to design specs and the hairpin match too.
And i see aconsiderable SWR on my meter. How do i know it is the match or the elements that are out of spec?

You are correct,How will you know that even your SWR METER is working correctly?


Enough antennas and hairpin matches have been made to accept that when correctly cut and constructed that
'something else' must be wrong when impedance is not acceptable.

Offline Greekman

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #5 on: January 05, 2016, 02:27:57 AM »
New question.....

The assembly of the feed point and match etc, is becoming intricate, especially in the way it integrates in the boom...
At this point I need a proof of concept before going further into construction.

So, is it possible to asssemble on a piece of wood only the driven elements without the reflector and directors and take meaningful SWR measurents?

I *think* it is as the driven elements would work like a dipole, and i think both this and a Yagi are about 70ohms of

Offline Carl

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #6 on: January 05, 2016, 06:42:26 AM »
The driven element can be tested alone,but is effected when additional elements are added or even located closer/farther from the driven element.

Offline Greekman

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #7 on: January 05, 2016, 06:53:02 AM »
you mean its tuning...it figures

Offline armymars

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #8 on: January 05, 2016, 03:53:20 PM »
  As you add more elements it will often lower the impedance of the antenna. Many 3 element beams have a impedance of 23 ohms or so. The hair pin match helps take care of this. Adjust the hair pin match first for the lowest SWR, then go up and down the band to see where the antenna likes to be. If it's not where you want it then adjust the driven element length. You might have to adjust the hair pin to fine tune it.

Offline Greekman

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Re: Inpedance matching for Collapsible Yagis (for field use)
« Reply #9 on: January 06, 2016, 02:16:43 AM »
thanks!