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[TowerTalk] Re: Question on Spacing for Ladder Line--and Match Box Tuner

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Subject: [TowerTalk] Re: Question on Spacing for Ladder Line--and Match Box Tuners
From: W8JI@contesting.com (Tom Rauch)
Date: Tue, 1 May 2001 06:02:31 -0400
> >  My question is what is the ideal width for the spacers ??
> >            tnx  Steve
>  I wonder if Steve ever got his question answered, about the IDEAL
>  WIDTH ?

It depends on many things, but any changes affecting loss can be 
tossed out because overall the loss is so low it doesn't matter.

The biggest problems are mechanical and how the impedance fits 
into your system. 

Mechanically, you want a wider spacing because the line is easier 
to build. 

Electrically, you want the closest spacing possible. It makes the 
line less critical to surrounding objects, it also makes the 
impedances presented at the end of the line more moderate on 
most bands when you feed unmatched antennas...like a 80 meter 
dipole fed with open wire to work all bands. Close spacing also 
minimizes radiation.

I use about 3 inches and solid bare copper wire. 

I have a 1500 foot long line using #8 solid copper wire spaced 2.75 
inches, and the measured loss in 1500 feet of length  (when 
matched) is about the same as 100 feet of RG-213 except on ten 
meters and above, where radiation starts to be a problem.

By the way, avoid feeding 1/2 wave dipoles with lines near an odd-
quarter wave long or multiple of an odd-quarter wave. You'll get real 
high impedances on a few bands, especially if the line impedance 
is high. For example, with a 600 ohm ohm line you'll get maybe 
6000 ohms on the lowest band...and a similar impedance on the 
next band up when the feeder is 1/2 wl long on the lowest band.

Use a 1/8th wavelength or 3/8th wavelength (etc, odd-1/8th wave) 
feeder on the lowest band, and the impedance is moderate on both 
bands.

The Match Box won't handle wide impedance ranges like a T 
network will.




  







73, Tom W8JI
W8JI@contesting.com 

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