I put on my safari hat and lots of bug repellent and took a trip out to my
closest 160M and 80M inverted coaxial Ls.
The base plates of these antennas are next to each other.
The SWR on the 160M feedpoint went from 1.1 at 1.800 to 1.9 at 2.000. (7 large
diamater radials)
The SWR on the 80M feedpoint went from 1.8 at 3.500 down to 1.1 at 3.79 and
back to 2.0 at 4.000 (30 radials, of
which 10 are large diameter).
Large diamater radials are scrap coax (cable tv, RG8, RG8x, etc). Normal
radials vary from #10 to #20. All radials
were cut according to the data (239.2/F) from the original CQ article. In the
case of radials that cross the lawn. I
use aluminum fence staples (They were in pristine condition after 10 years in
the ground in Iowa) and if the lawn
mower does not cut any radials, then it is time to install another group.
This is a new installation, so the number of radials will increase considerably
over the next couple of months. My
goal is 60 radials on each inverted L.
I always place results over theory. These antennas are 'heard' consistently
and hear pretty decently (I hope to start
experimenting with a beverage for 160M this winter. I usually run 500 watts
out at the most; usually less.
73
Bruce
On 14 Jul 2006 at 9:03, hasan schiers wrote:
> Inverted L's have similar bandwidth to a 1/4 wave vertical...and it isn't
> "real broad" without excessive return loss. All measurements need to be made
> at the feedpoint. I've done radial studies on my Inverted L and as radial
> numbers increase, vswr bandwidth DECREASES, exactly as it should. I made
> measurements of feedpoint Z at resonance and 2:1 vswr bandwidth with the
> following number of radials:
>
> 0,2,4,6,8,12,16,26
>
> VSWR bandwidth was best with 0 radials (DUH...lots of resistive loss!)
> Feedpoint Z dropped from 79 ohms with 0 radials to 29 ohms with 26 radials.
> The predicted Rrad is 25.4 ohms
>
> 73,
>
> ...hasan, N0AN
> ----- Original Message -----
> From: "Robert Chudek - K0RC" <k0rc@citlink.net>
> To: <towertalk@contesting.com>
> Sent: Thursday, July 13, 2006 5:50 PM
> Subject: Re: [TowerTalk] Question on Multiple Inverted L Antennas
>
>
> > Gentlemen...
> >
> > Here we go again... so which is it? Inverted L's have plenty of bandwidth
> > or Inverted L's little bandwidth???
> >
> > First, let me say if you are not taking your measurements AT THE
> > FEEDPOINT, you are not seeing the true story. Second, a large bandwidth is
> > not necessarily a good thing. The longer and more lossy your transmission
> > line, the better your antenna is going to look from the shack.
> >
> > Here's an example of what I'm talking about... I have a low 160m inverted
> > vee which I plotted VSWR graphs at the feedpoint and again at the end of
> > 230 feet of rg8x coax. I made absolutely no antenna changes between these
> > two measurements. I posted the superimposed VSWR and RETURN LOSS curves on
> > my website, here: http://tinyurl.com/oh87y The two PDF files are 72-KB
> > each and can be downloaded and viewed using Adobe Acrobat Reader.
> >
> > In this specific example, measuring at the end of the coax leads you to
> > believe you have 35% better bandwidth than in reality.
> >
> > 73 de Bob - K0RC
> >
> >
> >
> >> On 13 Jul 2006 13:20 WA3AFS wrote:
> >>
> >> Please be aware that the bandwidth for a coaxial inverted L is very
> >> broad. My SWR at 1.800 is 1.3 and slowly rises to 1.7 at 2.000Mhz.
> >>
> >
> > But then on 13 Jul 2006 at 13:11, K4SAV wrote:
> >
> >>> The biggest problem you have with low band multiple L antennas is
> >>> matching and bandwidth. To start with, a 160 meter L will not have a lot
> >>> of bandwidth...
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
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> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
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