[Antennas] Balanced line optimum conductor spacing?

Sat, 5 Jan 2002 15:54:31 -0800

Appreciate the discussion this seems to have kicked off. It has been
(mostly) interesting and informative, but it still hasn't quite gotten at
what I was wondering.

I guess I knew there was a formula for calculating the impedance of a
parallel conductor balanced transmission line given the wire diameter and
spacing (perhaps ignoring a few other minor parameters), though I didn't
have it at my fingertips. If that were all that mattered, we would use very
wide spaced lines to reduce losses. The other half of this question is how
to balance this against the desire to maintain canceling radiated fields
from our transmission line. When the spacing gets too wide with respect to
wavelength, our transmission line begins to be more antenna than
transmission line. What I'm looking for is some practical guideline limits
to this.

Again, what would be useful would be a rule of thumb along the lines of
"conductor spacing should be between something like 0.1% of wavelength and
0.5% of wavelength". This is going to be somewhat subjective in terms of how
much radiation we can tolerate vs how much loss we can tolerate, but it
seems to me we should be able to come up with some sort of useful
guidelines.

- Tom Scott, Field Applications Engineering
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-----Original Message-----
From:	[email protected] [mailto:[email protected]]
On Behalf Of Dan Richardson
Sent:	Saturday, January 05, 2002 3:28 PM
To:	[email protected]
Subject:	Re: [Antennas] Balanced line optimum conductor spacing?

My apologies Chris I thought of that after I clicked the send button. Here
it is in a little easier format:

Z = 2.718283 * [D/d]

Where D = The center to center distance of the conductors
            d = The diameter of the conductors

Actually if you want to be *really* fussy a better figure to use would be
2.718281828459 - The decimal string is endless.

The above is more accurate that the formula give in the ARRL hand book   Z
= 276log [2D/d]

Again sorry and hopes this helps.

Danny, K6MHE

  At 02:22 PM 1/5/2002 -0800, you wrote:
>I donot intend to be critical but
>The last time I heard about hyperbolic trinometric functions was when I
>was trying to teach an engineer some physics.  That may be the correct
>formula but I am sure there exits a number of simple formulas that will
>give good results for an amateur radio hobbist.
>It is a little bit like when a frosh and a freshette are intruduced and
>close the distance between them by one half every 3
>minutes.  Theoretically they will never meet but (nomatter how for the
>first distance was) in a very short time  it doesnot matter.
>
>Chris opr VE7HCB

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