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Author Topic: Hexagonal beam balun?  (Read 1347 times)
W1JKA
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Posts: 1674




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« on: October 12, 2012, 01:25:10 PM »

  Knowledge needed: Just finished making a 20m homebrew hexagonal beam  from a a patio table umbrella frame and as I only operate qrp 5w or less is a balun needed? If so I will make one with 7 turns of coax on a Folgers plastic coffee can.Thanks for any input.  Jim
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N3JBH
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« Reply #1 on: October 12, 2012, 02:18:58 PM »

I doubt 7 turns of coax is going to offer you much to be honest at that frequency.  maybe 15 turns of RG-58 over a 4" piece of pvc would.
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WB6BYU
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« Reply #2 on: October 12, 2012, 03:15:09 PM »

Whether or not you need to use a balun depends on how consistent you want the
pattern and performance to be with changes in feedline length, etc.

If it doesn't matter that sometimes radiation from the coax shifts the pattern and
fills in nulls, or that noise from your house might get picked up on the feedline,
then you don't need one.

If you do decide to use one, G3TXQ has some excellent advice about the effectiveness
of various types of coax chokes here:

http://www.karinya.net/g3txq/chokes/
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G3TXQ
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« Reply #3 on: October 13, 2012, 01:48:46 AM »

Even using low power, common-mode current can still cause problems: pattern distortion, and increased noise pick-up on Rx.

Coiled-coax chokes are quite narrowband, and their "centre frequency" shifts significantly with different implementations; so a broadband ferrite-cored choke is the safe option. But, if you're determined to go with the coiled-coax option, 7 turns is not enough; as N3JBH said, 15 turns of RG58 on a 4" form is about optimum for 20m use.

Congratulations on the hexbeam build!

73,
Steve G3TXQ
« Last Edit: October 13, 2012, 01:52:39 AM by G3TXQ » Logged
W1JKA
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« Reply #4 on: October 13, 2012, 08:19:36 AM »

    Thank you gentlemen for your timely expert advice.Since this is another one of my no cost antenna projects from on hand and scrounged parts I will make the 15 turn on 4 in.pipe balun that you all mentioned and see how that goes.I am building this from your website plans Steve,thanks for providing them.My (tower) is a 10 ft. aluminum extension ladder with a 10 ft. tv antenna mast for an extension  that I got free at the local landfill set aside pile,it will give me about 28 ft. height ,rotator is an armstrong model with a pipewrench controler that I also found at the dump HI.  73  Jim
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K8AC
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« Reply #5 on: October 13, 2012, 08:33:11 AM »

Quote
rotator is an armstrong model with a pipewrench controler that I also found at the dump

Good for you, Jim!  That brings back memories of my first beam, a three element 10 meter job made out of steel electrical conduit and rotated with - a pipe wrench.

73, Floyd - K8AC
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WB6BYU
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« Reply #6 on: October 13, 2012, 09:49:15 AM »

I didn't even have a pipe wrench for a rotator - I stepped out the front door and
put on a pair of leather gloves.
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