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Author Topic: The age old ladder line to coax balun question!  (Read 1364 times)
NZ0T
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Posts: 74




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« on: April 05, 2009, 07:33:09 PM »

I just got the Wireman 832 balun kit and it looks to be a fun project.  I am planning to use this on a 160 meter doublet cut for 1.947 Mhz and fed with 450 ohm ladder line to a short piece of coax.  I have been using a cheap 4:1 balun between the LL and coax and an MFJ 949C manual tuner.  This has worked fine on all bands 160 - 10 meters with the ability to get a good 1:1 match.  I recently acquired an LDG Z-100 automatic tuner as part of a rig trade and I thought it would be nice to use it with this antenna.  I works OK but struggles to find a match (1.5:1 or less) on 80 and 160 that will allow my Icom IC-706 to put out full output.  I ordered the kit thinking that a 1:1 balun might be better than the 4:1 I currently have.  Does everyone agree or should I make another (and much better) 4:1 balun from the kit?  I know I'm asking a lot of the little LDG and it may not be possible to match such a wide range of frequencies and impedance but I though I would pick the forums collective brain to see which balun would give me the best chance.

Thanks and 73,

Bill NZ0T
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K4SAV
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Posts: 1816




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« Reply #1 on: April 05, 2009, 11:02:19 PM »

Depends on the length of your feedlines.  Likely the impedance at the rig end has a low resistive part and a high reactive part which is always difficult to match especially on 160.  A 4 to1 balun would make that worse.

Jerry, K4SAV
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WX7G
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Posts: 5919




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« Reply #2 on: April 06, 2009, 07:24:17 AM »

The balun paper at DX Engineering, authored by Tom, W8JI, makes a good case for a 1:1 current balun in your situation. My limited analysis confirms this.

All of this addresses the balun itself and does not say whether your tuner will work better or worse.

One change you might make is to connect the ladder line to two lengths of coax configured as differential line. At the tuner place the 1:1 balun.

The coax is connected like so: Inner conductor of each coax to the balun. TX end of shields to tuner GND. Ladder line end of coax shields tied together and not connected to anything.

With this arrangement we end up with half the voltage on each coaxial cable as compared to the single coax case.

I can run an EZNEC simulation to see what if any advantage this affords you.
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NZ0T
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Posts: 74




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« Reply #3 on: April 06, 2009, 12:39:45 PM »

Do the 2 lengths of coax have to be separated like the ladder line?  If not I could do that - the coax enters the shack through a length of 1.5" PVC pipe.  
I really appreciate the help.
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