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Like info on number of wraps needed to make "Ugly Balun" using 8x Coax

Mudduckmobile

Mudduckmobile

Well-Known Member
Oct 5, 2015
639
339
73
S.W. Washington Coast
I would like to build....wrap up a Balun (ugly) using 8x coax to put under a 108in s.s. whip mobile antenna.
Need to know outside diameter of PVC pipe to use, and number of wraps with coax.
Thank you.
Oh this is for the 11 meter band.
73
 

choke_impedances.png
 
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Mudduckmobile said:
I would like to build....wrap up a Balun (ugly) using 8x coax to put under a 108in s.s. whip mobile antenna.
Need to know outside diameter of PVC pipe to use, and number of wraps with coax.
Thank you.
Oh this is for the 11 meter band.
73
Click to expand...
Why a Balun??? A balun is basically for balancing an UN-balanced line. Hence the name BAL-UN. They are also used for transforming different impedance's like converting a 450 ohm feed line to 50 ohms. etc.

What you need here I believe is a matching device since you probably discovered a 108 whip isn't 50 ohms.

Get some 14 gauge enameled wire and wrap 7 to 9 turns around a spark plug thread to form a nice coil. Solder some ring terminals on each end and attach it to your antenna on the HOT side and the Ground side to form a shunt. Use an antenna analyzer and either stretch the coil or compress it to get it to 50 ohms. You may have to take a coil turn or 2 out to get there but an antenna analyzer will show you which way to go.

If it common mode you are tying to control, it's far easier on a mobile setup and works well to wrap 7 turns of RG 8x coax about 5 inches or so in diameter and clamp on one 3/4 inch mix 31 ferrite bead on it and be done with it. You can get the proper mix 31 ferrite beads at DX engineering.

Doing this will de-tune your antenna some, but that's what the shunt coil at the antenna feed point will compensate for.

coaxchoke.jpg
 
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Don't forget to take the diameter of the coax itself into consideration. Check the specification for the type. RG-8, RG-213 and other cables with an OD of ~0.405 inches usually requires around 8 inches in diameter (diameter = twice the radius).

RG-8X is usually right at 0.25 inches OD, so I'd figure 5" diameter for a coil.
 
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if you are running legal.. forget about all that...
get an analyzer and start trimming that 108" down...
you will wind up some where around 102" for the 11 meter band...if you are playing games, then follow the advice fourstringburn gave you... an analyzer and a field strength meter are your friends... The ugly balun (choke actually) in this case will not do you much good...except for common mode current feedback if you are running power...
 
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Obed said:
if you are playing games,
Click to expand...

What do you mean by playing games? Learning how to match impedance's is a valuable lesson may be you should learn too.

Trimming down the antenna will not bring this antenna feed point impedance to 50 ohms. Depending on where he want's the resonant point at, he may have to do so anyway.

Will it make a difference? not so much but the point is to get your hands dirty and learn something in the process.
 
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fourstringburn said:
What do you mean by playing games? Learning how to match impedance's is a valuable lesson may be you should learn too.

Trimming down the antenna will not bring this antenna feed point impedance to 50 ohms. Depending on where he want's the resonant point at, he may have to do so anyway.

Will it make a difference? not so much but the point is to get your hands dirty and learn something in the process.
Click to expand...
I do know what you mean. In the past, I would just put some antenna on my car/truck, set the swr best I could,a nd not even think about the "why I 'm I doing this" or what does this mean, when I was reading my antenna analyzer. You know I just put the antenna up as high and clear of things I could. I bonded EVERYTHING top to bottom. Now I am doing it all RIGHT as I can from what I have learned here, and from all the good write ups on K0BG (s) page. In the pasted I have been lucky...ignorance WAS bliss....and no gear was fried... I thank you all for the help, Now I work with it.
73
 

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