450 ohm feedline to a multiband vertical
 

I sometimes use a 33 foot vertical with 16 25 foot radials laying on the
ground. I feed this with 450 ohm window line and use it multiband. It is
an excellent performer for me. I want to understand what is happening at
the feedpoint on 20 meters and 40 meters on both conductors of the
feedline.

--
Bob Kimbrell W7KU Kansas City, MO

http://kimbrell.freeshell.org/
SDF Public Access UNIX System - http://sdf.lonestar.org

450 ohm feedline to a multiband vertical
 

On Wed, 7 Nov 2007 17:35:10 +0000 (UTC), "Robert M. Kimbrell"
wrote:

I sometimes use a 33 foot vertical with 16 25 foot radials laying on the
ground. I feed this with 450 ohm window line and use it multiband. It is
an excellent performer for me. I want to understand what is happening at
the feedpoint on 20 meters and 40 meters on both conductors of the
feedline.

Hi Bob,

At least one feedline conductor is a miserable horizontal radiator.
However, with this excellent performer, don't look for cavities in the
oral opening of an Equine.

73's
Richard Clark, KB7QHC

450 ohm feedline to a multiband vertical
 

Robert M. Kimbrell wrote:
I sometimes use a 33 foot vertical with 16 25 foot radials laying on the
ground. I feed this with 450 ohm window line and use it multiband. It is
an excellent performer for me. I want to understand what is happening at
the feedpoint on 20 meters and 40 meters on both conductors of the
feedline.

Assuming the feedpoint impedance on 40m is somewhere
around 35 ohms, the 40m SWR on the 450 ohm line would
be around 13:1. Assuming the feedpoint impedance on
20m is around 1200 ohms, the 20m SWR on the 450 ohm
line would be around 3:1. You probably should make
the ladder-line somewhere around an integer number of
1/2 wavelengths long on 40m and your tuner should be
able to handle the rest. You will have some common
mode current in the system that could cause some
radiation and losses from the ladder-line.
--
73, Cecil http://www.w5dxp.com

450 ohm feedline to a multiband vertical
 

An old answer for multiband the easy way was a 22 foot vertical with
22 foot radials and open wire feed... I like yours better because your
vertical is taller...

denny / k8do

450 ohm feedline to a multiband vertical
 

Denny wrote:

An old answer for multiband the easy way was a 22 foot vertical with
22 foot radials and open wire feed... I like yours better because your
vertical is taller...

Which makes it fairly useless on 10m. 22 ft is just
about the maximum monopole height for good low
angle radiation on 10m. 17m is just about the
highest useful frequency for a 33 ft. monopole.

I had very good performance on 40m-10m feeding the
22 foot system with an SG-230.
--
73, Cecil http://www.w5dxp.com

450 ohm feedline to a multiband vertical
 

Cecil Moore wrote:

: Assuming the feedpoint impedance on 40m is somewhere
: around 35 ohms, the 40m SWR on the 450 ohm line would
: be around 13:1. Assuming the feedpoint impedance on
: 20m is around 1200 ohms, the 20m SWR on the 450 ohm
: line would be around 3:1.

What I am trying to understand is the current on each conductor of the 450
ohm line. Are the radials a high impedance on 20 meters with a 33 foot
radiator? I can disconnect the radials and have an endfed zep and it
works ok. Connecting the radials makes the antenna perform better and the
tuning is different on the tuner in the shack.

--
Bob Kimbrell W7KU Kansas City, MO

http://kimbrell.freeshell.org/
SDF Public Access UNIX System - http://sdf.lonestar.org

450 ohm feedline to a multiband vertical
 

Robert M. Kimbrell wrote:
Are the radials a high impedance on 20 meters with a 33 foot
radiator?

No, 25 foot radials laying on the ground are not a
high impedance on 20m. One side of the feedline sees
about 1200 ohms, the other side sees an impedance
probably much lower than 1200 ohms.

I can disconnect the radials and have an endfed zep and it
works ok.

With an unbalance of the currents. One side sees about
1200 ohms, the other side sees an open-circuit. An endfed
Zepp requires 1/4WL of feedline. Is your feedline an
odd multiple of 1/4WLs on 20m? Probably not unless you
designed it that way.

Connecting the radials makes the antenna perform better and the
tuning is different on the tuner in the shack.

Either way, you have common-mode currents on the feedline.
The radial configuration doesn't require 1/4WL of feedline
and may just be more efficient.
--
73, Cecil http://www.w5dxp.com

450 ohm feedline to a multiband vertical
 

Which makes it fairly useless on 10m. 22 ft is just
about the maximum monopole height for good low
angle radiation on 10m. 17m is just about the
highest useful frequency for a 33 ft. monopole.


I get a nose bleed when the radio tunes that high....

denny / k8do