Topband: Impedance of inv l?

[k8gg at voyager.net]

Hi All,

Frank is correct.  We originally designed the Battle Creek Special to use
16 radials 1/4 wavelength long on 160 (about 135 ft each) and then found
that 32 radials 1/8 wavelength long (about 70 ft each) were much better
for 160, 80 and 40 meter radiation.

With 50 feet of mast and an 80 meter trap on top and the top loading wire,
the feed point impedance on 160 is about 25 ohms, of which almost half is
ground losses as determined by a DXpedition on a Pacific island that found
a 13 ohm feed point on a beach over salt water.

GL, 73,  George,  K8GG





>
> Hi Jamie,
>
>
> I use my AA-54 frequently in exactly the manner you're using your
> AA-23, I've never had any reason to be suspicious of any of its
> readings. I'm lucky to have no AM broadcast stations within ten
> miles.
>
>
> Your AA-230 is telling you that at least half of your power is being
> lost to ground resistance and need to at least double the number of
> radials to significantly reduce your resistive losses.
>
>
> The 2000 feet of wire in your radial system likely would have produced
> much better results with twice as many radials of half the radial length
> you used. Quarter wavelength radials aren't cost effective until many
> more than 60 radials are used.
>
>
> www.w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html
>
>
> 73
> Frank
> W3LPL
>
>
>
>
> ----- Original Message -----
>
> From: "Jamie WW3S" <ww3s at zoominternet.net>
> To: "Topband" <topband at contesting.com>
> Sent: Sunday, November 18, 2018 10:33:13 PM
> Subject: Re: Topband: Impedance of inv l?
>
> several have asked how I am measuring the impedance.....I'm using an
> AA-230,
> and am all the ALL PARAMS setting.....the 230 defaults to a series model,
> is
> that what I want, don’t see how to change it to parallel. I think the
> symbol
> for impedance is |Z|, correct?
>
> -----Original Message-----
> From: F Z_Bruce
> Sent: Sunday, November 18, 2018 3:20 PM
> To: wes_n7ws at triconet.org ; Topband
> Subject: Re: Topband: Impedance of inv l?
>
>
> The far end is high impedance voltage, and has minimum  horizontal
> current radiation.  The inverted L is a good trade off signal vs
> available height.  Not an expensive antenna to build. 
>
> 73
> Bruce-k1fz 
>  
> On Sun, 18 Nov 2018 12:31:38 -0700, Wes Stewart wrote:
>
> That also drives up the current in the horizontal wire with attendant
> increased
> horizontal radiation.
>
> I chose for a couple of reason to do the opposite; shorten the wire to
> make
> the
> feedpoint capacitive and use a shunt inductor to get a 50-ohm match. 
> This
> really doesn't improve the 2:1 VSWR, that I consider acceptable, however.
>
> Wes  N7WS
>
> On 11/18/2018 8:55 AM, F Z_Bruce wrote:
> > That sounds about right. As you put a good ground system under it,
> that
> value will come down, and the efficiency will come up.
> >
> > Many add extra antenna wire that pushes the current up the wire, this
> also raises  the impedance, hopefully to near 50 ohms with the right
> length.
> > A capacitor (variable, then fixed) in series at the feed point can
> cancel the added inductance.
> >
> > 73
> > Bruce-k1fz
> > https://www.qsl.net/k1fz/beverage_antenna.html
> >
> >  
> > On Sun, 18 Nov 2018 10:41:36 -0500, WW3S wrote:
> >
> > What should the Z be for a 1/4 wave inv l, with the radials attached
> to
> a radial plate? Mine seems to be 60 ohms or so....
> >
> > Sent from my iPad
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