Oh, by the way, the modeling I did was over real earth.
---- Dennis <radioart@charter.net> wrote:
> Hi Chuck,
>
> At the minimum you would want to use a high power balun to interface the
> unballanced coax with the ballanced 450 ohm line. As to why type or
> impediance of balun, that would be determined by the impediance of the 450
> ohm line at the operating frequency you intend to operate. I ran some
> numbers using EZNEC +5.0 for a 135' inverted V dipole 40' high at the center
> and 10' high at each end. I modeled the 90' of 450 ohm line you said you
> could use. Here is what I got:
>
> Freq. R J
> 3.8 46 -59
> 7.2 31 -71
> 14.2 170 +677
> 21.3 159 -486
> 28.5 130 +254
>
> AS you can see the R ohms would work for a 1:1 balun on 80m and 40m but a 2
> or 3:1 balun would work better on 20m, 15m and 10m. The J ohms are reactance
> caused by the length of the antenna not being exact multipuls of the
> frequencies I used on my calculations. For this reason, at home, I bring
> the 450 ohm line in through the window and use a Johnson KW matchbox to
> provide an EXACT match to the 50 ohm line at any frequency. You could adjust
> the antenna length to give a lower J at the operating frequencies if you are
> not able to use a good ballance antennal tuner.
>
> I do not know what stress you would place on the balun if you tried to use
> one size to fit all but ,what the heck, its only a hobby....
>
> Hope this helps,
>
> Dennis ,k0eoo
>
>
>
> ---- KI9A@aol.com wrote:
> > Gang-
> >
> > After some serious tree trimming, I now have room to fit a full sized wire
> > antenna where my G5RV is right now. I am thinking about a 135' open wire
> > fed
> > dipole, as multi bands are needed.
> >
> > Question is this- there is now way I can get 450 ohm feedline into the
> > shack. The best I can do is about 30' of RG213, then the rest 450 ohm (
> > maybe
> > 90'). Is this going to be a waste of my time, or is it worth it? I'd
> > obviously
> > use a balun to change over to 50 ohm feedline.
> >
> > 73- Chuck KI9A
> >
> >
> >
> > **************It's only a deal if it's where you want to go. Find your
> > travel
> > deal here.
> > (http://information.travel.aol.com/deals?ncid=aoltrv00050000000047)
> > _______________________________________________
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