Matching Issue ........... I think!
 

On Wed, 31 Jan 2007 20:42:51 -1000, wrote:

so whats the solution to making it work on 40? a tuner?
some kind of tuned piece of coax?????????????

Read Owen's reply.

73's
Richard Clark, KB7QHC

Matching Issue ........... I think!
 

wrote:
maybe I should have asked does my coax tune my antenna???????

When the load impedance is not 50 ohms and the
target impedance is 50 ohms, 50 ohm coax cannot
tune your antenna system to a 50 ohm match. In fact,
using 50 ohm coax with an SWR not equal to 1:1 is
one way of guaranteeing that the transmitter will
*never* see 50 ohms without some help from a
tuner or other matching method. (Extensive losses
will also bring the SWR closer to 1:1).

If the target impedance is 50 ohms, only a
characteristic impedance different from 50 ohms
can transform the non-50 ohm impedance to 50
ohms. And that can only be done when the SWR is
not 1:1. Note that in Owen's 1/4WL matching
equation, only if the load and source are both 50
ohms does the equation result in Z0 = 50 ohms.
Such a system is called a "flat" system with a
trivial default SWR of 1:1.

An autotuner at the feedpoint will solve the
problem or a parallel feedline with a Z0 of
300-600 ohms will solve the problem. I have
solved the problem at my QTH with a 148 foot
dipole and 90 feet of 450 ohm ladder-line.
That antenna system is simultaneously resonant
at my QTH on both 7.15 MHz and 3.8 MHz at the
same time. And it is also close to resonance on
17m.
--
73, Cecil http://www.w5dxp.com

Matching Issue ........... I think!
 

wrote:
so whats the solution to making it work on 40? a tuner?
some kind of tuned piece of coax?????????????

A better description would help. That looks more
like a ground plane antenna than it does a dipole.
Please describe the antenna in more detail.
--
73, Cecil http://www.w5dxp.com

Matching Issue ........... I think!
 

Hmmm, I can't make much of this diagram and the group has decided to
use passive aggressive behavior to "teach you"... You are asking for
help and getting didactics thrown in your face... Shame on them!

I doubt you can feed this antenna on 40 with coax... You will need to
either put a tuner at the feed point, or resort to open wire line and
a tuner at the radio...

My first impulse would be to turn this into a top loaded vertical with
an elevated counterpoise, the vertical self resonant on 40 and loaded
for 80...
Feed it at the bottom of the vertical section with the braid going to
the 17 foot horizontals (some tuning needed)... Use a loading coil
about half way up the vertical for 80 and short it out for 40... The
counterpoise (the 17 foot horizontals as best I can make out) would be
coil loaded at at the center connection of the 2 "radials" so they
are resonant on 80 with a shroting clip for 40... A relay will select
for you, or you can walk out and manually move the clips...

Go to the library there and get an interloan copy of Moxon's "HF
Antennas for all locations"... He has an excellent discussion of
loaded radials/counterpoises, etc... With his help you should see how
to make your antenna play... Any problems drop me an email through
and I will give you a fax number where you can shoot me
a diagram of your antenna and we can discuss it...

cheers ... denny / k8do

Matching Issue ........... I think!
 

wrote in
:


its half wave


I would not have guessed that from the meagre information you supplied.

Owen

Matching Issue ........... I think!
 

Cecil Moore wrote:

wrote:
maybe I should have asked does my coax tune my antenna???????

When the load impedance is not 50 ohms and the
target impedance is 50 ohms, 50 ohm coax cannot
tune your antenna system to a 50 ohm match. In fact,
using 50 ohm coax with an SWR not equal to 1:1 is
one way of guaranteeing that the transmitter will
*never* see 50 ohms without some help from a
tuner or other matching method. (Extensive losses
will also bring the SWR closer to 1:1).

If the target impedance is 50 ohms, only a
characteristic impedance different from 50 ohms
can transform the non-50 ohm impedance to 50
ohms. And that can only be done when the SWR is
not 1:1. Note that in Owen's 1/4WL matching
equation, only if the load and source are both 50
ohms does the equation result in Z0 = 50 ohms.
Such a system is called a "flat" system with a
trivial default SWR of 1:1.

An autotuner at the feedpoint will solve the
problem or a parallel feedline with a Z0 of
300-600 ohms will solve the problem. I have
solved the problem at my QTH with a 148 foot
dipole and 90 feet of 450 ohm ladder-line.
That antenna system is simultaneously resonant
at my QTH on both 7.15 MHz and 3.8 MHz at the
same time. And it is also close to resonance on
17m.

can this be done with one feedline?

--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!

Matching Issue ........... I think!
 

Denny wrote:

Hmmm, I can't make much of this diagram and the group has decided to
use passive aggressive behavior to "teach you"... You are asking for
help and getting didactics thrown in your face... Shame on them!

I doubt you can feed this antenna on 40 with coax... You will need to
either put a tuner at the feed point, or resort to open wire line and
a tuner at the radio...

My first impulse would be to turn this into a top loaded vertical with
an elevated counterpoise, the vertical self resonant on 40 and loaded
for 80...
Feed it at the bottom of the vertical section with the braid going to
the 17 foot horizontals (some tuning needed)... Use a loading coil
about half way up the vertical for 80 and short it out for 40... The
counterpoise (the 17 foot horizontals as best I can make out) would be
coil loaded at at the center connection of the 2 "radials" so they
are resonant on 80 with a shroting clip for 40... A relay will select
for you, or you can walk out and manually move the clips...

Go to the library there and get an interloan copy of Moxon's "HF
Antennas for all locations"... He has an excellent discussion of
loaded radials/counterpoises, etc... With his help you should see how
to make your antenna play... Any problems drop me an email through
and I will give you a fax number where you can shoot me
a diagram of your antenna and we can discuss it...

cheers ... denny / k8do


the physical antenna stays as is and works extremely well on 75.
What has me asking the questions is that I was told a 1/4 wave piece of coax
would get it to work on 40.

Maybe I need to run it thru some modeling software and see what actually
does need to happen to get 40 to work.


--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!

Matching Issue ........... I think!
 

Cecil Moore wrote:

wrote:
so whats the solution to making it work on 40? a tuner?
some kind of tuned piece of coax?????????????

A better description would help. That looks more
like a ground plane antenna than it does a dipole.
Please describe the antenna in more detail.

go to Force 12 website and check out the sigma 80

this is similar in that instead of having horizontal elements on the top its
straight vertical.

signal reports on 80 have been very impressive.


--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!

Matching Issue ........... I think!
 

On Thu, 01 Feb 2007 19:32:05 -1000, wrote:

signal reports on 80 have been very impressive.

You sound like a very good customer prospect weighed against the
testimonials offered to a German inventor of a 9 foot tall 160M
radiator.

Signal reports on 80 still doesn't make it work on 40M however. The
reasons have been explained for your difficulties, and solutions
offered. Are you looking for something different?

73's
Richard Clark, KB7QHC

Matching Issue ........... I think!
 

wrote:
I have
solved the problem at my QTH with a 148 foot
dipole and 90 feet of 450 ohm ladder-line.
That antenna system is simultaneously resonant
at my QTH on both 7.15 MHz and 3.8 MHz at the
same time. And it is also close to resonance on
17m.

can this be done with one feedline?

Yes, I have done it with one feedline and written
an article for "Worldradio" about it.
--
73, Cecil http://www.w5dxp.com