[Antennas] Simple Dipole Question

[Jerry Flanders]

At 18:14 10/24/02 -0500, Kelley Shaddrick wrote:
>Thanks to all for the replies, a whole host of information.
>
>After some fiddling around with it, the antenna is now down to about 1.3:1
>or so at about 14.1 MHz going to 2.5 at 14.35 MHz. I shortened the ladder
>line and lengthened the antenna a bit to get it there. Seems very narrow
>banded.

It appears narrow banded because of the effect of the ladder line. As the=20
wavelength changes, the effective electrical length of the LL changes. The=
=20
greater the length of the LL (in half-wavelengths), the greater the effect.

See w5dxp's discussion at his "W5DXP's No-Tuner All-HF-Band Antenna"
  page link from http://www.qsl.net/w5dxp for the reason lengthening the=20
antenna along with shortening the LL worked.

You might be interested in knowing that you can find combinations of dipole=
=20
length and LL length that allow the system to work simultaneously on=20
several bands at a time. I have a LL-fed 85 foot dipole that works at low=20
SWR with no tuner on 10, 15, and 20. w5dxp has a program at the above link=
=20
that helps to show just what lengths of antenna and LL are needed. I=20
fine-tuned mine with an antenna analyzer after getting the basic design=20
from w5dxp's site.

The demo EZNEC program would also show this - use the TL-fed dipole example=
=20
and play with the dimensions while running a wide frequency sweep.

Jerry W4UK
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

>Anyway, why didn't I use coax? I didn't have any and there's no place
>locally to get any. I used what I had, a few feet of RG-8X and some ladder
>line. Sorry, no antenna anaylzer either in this end, maybe some day.
>
>I'll probably rehang the antenna with coax, but it was an interesting
>experiment.
>
>Thanks to all,
>
>Kelley -- W=D8RK
>
>----- Original Message -----
>From: "Kelley Shaddrick" <kshaddri@xtratyme.com>
>To: <antennas@mailman.qth.net>
>Sent: Thursday, October 24, 2002 2:24 PM
>Subject: [Antennas] Simple Dipole Question
>
>
> > Today, with nothing better to do, I stuck up a dipole cut for 20m (14.2
>MHz)
> > using 468/frequency. It's strung between two trees at about 50 feet in=
 the
> > air. I fed it with ladder line (450 ohm) to the house (about 100 feet)=
 to
>a
> > 1:1 balun and some RG-8X (about 20 feet) into the 2nd floor shack. The
> > initial swr reading is infinite across the band, no dip anywhere, not=
 even
>a
> > little. I suppose since I'm using ladder line, or window line, I need to
>cut
> > things different. Any thoughts?
> >
> > Thanks,
> >
> > Kelley -- W=D8RK
> >
> > - - -
> >