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Author Topic: Inverted L Balun  (Read 2316 times)
KC2NYU
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Posts: 140




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« on: July 24, 2012, 06:37:06 PM »

Have RG213 running from shack to base of tree where I am going to run the vertical leg of an Inverted L. Antenna wire is 14 gauge, single stranded insulated THHN
and I am using above ground radials.
I plan to use a 1:1 balun between the coax and antenna/radials.
This may seem like a dumb question but want to be certain...  here goes. I would hook the antenna wire to one side of balun and then hook the radials to the other side of the balun???

Tnx and 73
Paul
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KF6ABU
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« Reply #1 on: July 24, 2012, 06:56:26 PM »

yep!
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WX7G
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« Reply #2 on: July 25, 2012, 08:03:56 AM »

The balun, or current choke, has an input (unbalanced end) and an isolated end. The feedline connects at the input end and the inverted-L wire and elevated radials connect at the other end.
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K3VAT
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« Reply #3 on: July 25, 2012, 08:18:47 AM »

Have RG213 running from shack to base of tree where I am going to run the vertical leg of an Inverted L. Antenna wire is 14 gauge, single stranded insulated THHN and I am using above ground radials.
I plan to use a 1:1 balun between the coax and antenna/radials.  Tnx and 73  Paul

Hi Paul,
I'm interested in your setup.  Is this a single band inverted L ... and for what band(s)?  How many above-ground radials are you considering with this?  Finally, what is the approx height of the feedpoint?

thanks, 73, Rich, K3VAT
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AA4PB
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« Reply #4 on: July 25, 2012, 08:37:17 AM »

The coax feed is unbalanced. The inverted-L is unbalanced. What does a 1:1 balun accomplish? A choke balun might keep RF off the outside of the coax feedline if your radials aren't providing an effective RF ground - but that means you have loss in the ground system.
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WB6BYU
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« Reply #5 on: July 25, 2012, 09:01:46 AM »

Quote from: AA4PB

The coax feed is unbalanced. The inverted-L is unbalanced. What does a 1:1 balun accomplish? A choke balun might keep RF off the outside of the coax feedline if your radials aren't providing an effective RF ground - but that means you have loss in the ground system.



You can still have common mode current on the feedline even when the ground system
has insignificant loss:  an elevated ground plane for VHF, for example, has very little loss
in the radials, but they still may not be sufficient to keep the outside of the coax from
acting like one of the radials.

So a 1 : 1 current balun ( = choke balun ) may help to reduce the receive noise level by
providing better decoupling of the feedline in some cases.  A voltage balun, however,
would be a poor choice in this application because both the feedline and the load are
unbalanced:  impressing equal voltages on ground and the antenna probably will
force common mode currents on the coax.
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N3JBH
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« Reply #6 on: July 25, 2012, 10:24:12 AM »

I like to check the continuity of the input SO-235 with the output studs. When i find the stud where it has continuity  with the center conductor i use that one to feed the antenna radiating element and the shield side for the ground/ radial's.  Of course i am referring to using a 1:1 current balun here. Whether my approach is right or not i am sure other will chime in on. Also i admit i am slightly anal about the way i make my antenna's. Just have this thought it work better this way.

Jeff
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W5DXP
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« Reply #7 on: July 25, 2012, 10:42:04 AM »

So a 1 : 1 current balun ( = choke balun ) may help to reduce the receive noise level by providing better decoupling of the feedline in some cases.

Might it be better to call such a device a UNUN (a la Sevick) i.e. an UNbalanced to UNbalanced device?
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