[Top] [All Lists]

Re: [TowerTalk] Coaxial Moxon

To: Brian Machesney <>
Subject: Re: [TowerTalk] Coaxial Moxon
From: "David J. Sourdis" <>
Date: Tue, 5 Aug 2008 01:31:14 -0500
List-post: <">>
Thank you all for the response. I made one dipole for 10m band with RG8 type, 
vf=.66, formula dictated about 1.75m for each half of the dipole. I started 
with 1.80m per side, and hung it about 2 meters above the floor, it was already 
dark and wasn't an optimal location, I will try today to install it somewhere 
else. The thing resonated at 23.5 Mhz, sure that in a higher and clear location 
it would get a little higher resonant frecuency. According to the Antenna Book, 
bent dipoles have a 0.55 frecuency factor, this would fall around 21,7 MHz for 
the lenght I am using. This factor is for a bent wire, not a for coax with 
dielectric and its specific geometry.

My initial conclusion is that it behaves like a dipole with each half bent so 
the tips get close to the center of the antena without touching each other, 
just like a folded dipole but opened at the center. So, IMHO, it is like a bent 
dipole that is 3,60m long on each half (the lenght of the center conductor plus 
the lenght of the shield added together). If it is so, the center half of the 
dipole with the most current area would be enclosed by the rest of the lenght 
which has the smaller current area. Forgetting about supposed shorter length 
advantage given by the velocity factor  and seeing it like a bent dipole, would 
be better to connect the shield to the feed line instead of the center 
conductor so the lenght with the least current is enclosed by the one with the 
greater current portion, more Watts transferred to the air.

Please anyone correct me if I am wrong, I am just an antenna aficionado, not a 
pro on the subject. 


> Date: Mon, 4 Aug 2008 09:07:38 -0400
> From:
> To:
> Subject: Re: [TowerTalk] Coaxial Moxon
> CC:
> David,
> I don't see any connection to the shield of the coax used in the
> driven element or the reflector (see drawing, "Center Conductor only
> is attached to feedline on both ends!"). It looks to me as though coax
> is being used as wire with a very thick dielectric coating. Since EM
> waves travel more slowly in any (known) medium other than free space,
> placing the wire in the dielectric causes it to look electrically
> longer.
> As far as I know, all dielectric coatings also have more loss than
> free space, so that may need to be accounted for in any analysis.
> Brian K1LI
> On 8/3/08, David J. Sourdis <> wrote:
> >
> >
> > A quarter wave coax, shorted at the end shows an infinite impedance.
> > Is it possible what is described in the link?
> >
> > David
> > HK1KXA
> > EC5KXA
> >
> >
> > _________________________________________________________________
> > Discover the new Windows Vista
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> >
> >
> >

Connect to the next generation of MSN Messenger

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>