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Author Topic: Using RG58 as Balanced Ladder Line /M  (Read 3526 times)
M0MCX
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« on: October 07, 2013, 12:58:43 PM »

Hi, I have an SG230 ATU connected to a Kenwood TS-2000 (with remote head) for mobile use.

I am making up 2 x 5 foot lengths of RG58 as balanced feeder for a miniature loaded doublet on the roof of my Merc (16 feet, copper wire, mildly helically wound carbon-fibre sail-board mast). Thye feeding principle is similar to this article: http://k9zw.wordpress.com/2008/08/02/ladder-line-building-pass-through-with-twin-coax-rg-8/

Question, should I connect the earth strap across the two coax lines to a) my car ground (negative earth), b) the ground lug on the SG230 or c) Leave it floating?

Thanks for your consideration.

Callum, M0MCX
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WB6BYU
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« Reply #1 on: October 07, 2013, 01:19:05 PM »

It probably doesn't make a lot of difference.  I'd ground it to the coax shield at the
input to the balun (assuming that is how you are driving the balanced line from the
autotuner) but you can try it either way and see if you hear a difference on receive.
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W5DXP
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« Reply #2 on: October 08, 2013, 04:58:16 AM »

I am making up 2 x 5 foot lengths of RG58 as balanced feeder for a miniature loaded doublet ...

If you tie the coax braids to the SG-230 ground terminal, zero RF current will flow in the center conductor of the coax connected to the ground terminal, i.e. the feedline is not balanced. You might as well just use one piece of coax with the braid connected to that ground terminal and a 1:1 choke at the dipole feedpoint. Note that the SG-230 is capable of developing voltages that will cause coax to arc.
« Last Edit: October 08, 2013, 05:03:01 AM by W5DXP » Logged
WX7G
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« Reply #3 on: October 08, 2013, 01:45:16 PM »

1) The correct connection at the TX end is the shield to the automobile/tuner chassis and each coax inner conductor to the balun output.
2) The shield at the dipole antenna end can be connected to the automobile body (make this connections short) or it can be left floating.

An equally effective way to feed the dipole is to run coax from the unbalanced tuner to a balun at the antenna.
« Last Edit: October 08, 2013, 01:47:44 PM by WX7G » Logged
K5LXP
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« Reply #4 on: October 08, 2013, 02:31:16 PM »

I'm trying to figure out what this thing looks like.

This is a 10ft vertical pole with 16 feet of helically wound wire, fed in the center 5 feet up with twin coax?


Mark K5LXP
Albuquerque, NM
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W5DXP
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« Reply #5 on: October 08, 2013, 04:49:51 PM »

1) The correct connection at the TX end is the shield to the automobile/tuner chassis and each coax inner conductor to the balun output.

I'm not sure a balun exists in the original description. My SG-230 manual recommends against connecting transmission lines to the output terminals.
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