Flumoxed

[k6dgw]

Robert: Yes, most of the radiation from a conductor originates in the
high current section(s) of the conductor, and for a half-wave dipole,
that's the center, low impedance part.  The sag will lower the center,
ergo the "gain" will decrease.  Whether or not it's enough to be
noticeable is questionable however, and may be off-set by the losses in
transforming the balanced line to unbalanced and the impedance
transformation required.  At some point in all this discussion, you will
find yourself trying to pick the fly poop out of the pepper [military
expression which I've cleaned up a little for this forum].

Related:  The voltage/current distribution on a conductor is determined
*only* by the length of the conductor measured in wavelengths.  It
doesn't matter how or where you inject the RF current.  A Buddipole in a
horizontal configuration is off-center fed because it is inherently
physically short and low, and the center impedance is also low ...
~20-30 ohms on 20 meters.  Moving the feed point out toward one end
raises the impedance seen by the 50 ohm transmission line.  It also
unbalances the entire system leading to undesirable current on the outer
surface of the coax shield conductor.

And, to the original subject I assigned to this thread, how many
remember the Windom feed that Novices, who couldn't afford transmission
line, used in the 50's.  Definitely "Less Than Perfect" but there are
QSO's in my log using it.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 12/8/2018 7:03 PM, Robert G Strickland wrote:

> Ron...
>
> Would such an antenna cut for 80m, fed with ladder-line, and used on
> 40m, be a better performer on either band than an 80-40m fan dipole
> fed with 72ohm coax? Leaving all other extraneous but influencing
> parameters aside. I have the second antenna; the weight of all that
> wire and the coax with a ferrite balun results in a significant sag.
> I'm wondering if the first antenna, lighter and higher in the air,
> would perform better? Thanks.
>
> ...robert
>

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The most extensive measurements of real live dipoles using chokes and baluns has been done by Rick DJ0IP.  He made hundreds, if not thousands of measurements with asymmetric dipoles.  He measured common mode current with the feeder straight down, off-centre and reversed on several bands to test his ideas.  This all culminated in products that Spiderbeam now sell world wide, likely the only ocfd that work properly.  He also has a section on his website called the Battle of the Baluns which is worth a read.  He's not into physics just sound, repeatable, practical measurements.  
David G3UNA

> On 09 December 2018 at 18:47 Jim Brown <[hidden email]> wrote:
>
>
> I wonder if anyone using or recommending products like this have ever
> measured them.  They are not easy to measure.  You can't measure them
> accurately with a single-port antenna analyzer.
>
> N6KT, a member of our contest club is building a station in the
> Caribbean and asked me to measure a Balun Designs 1115T common mode
> choke (often called a 1:1 current balun). It looks NOTHING like it's
> data sheet, which shows an approximately flat high choking impedance
> over the HF bands. It would be USELESS on 40, 80, and 160M! From what
> I've seen them write about chokes, I don't believe that they understand
> how common mode chokes work, and I certainly wouldn't suggest that
> someone ask them for advice.
>
> The Wireman 8232 is based on W2DU's excellent work from many years ago.
> He built chokes with 50, 100, and 200 of the largest #73 Fair-Rite beads
> that fit over RG142. This size bead of this material has the unique
> property of relatively constant choking impedance in the HF spectrum,
> but you have to a LOT of them.  Only the 200-bead choke has sufficient
> choking impedance to handle high power and kill receive noise, and
> that's what he recommended, yet most products sold as a "W2DU balun"
> have many fewer. The larger #31 cores are not useful at HF until you
> wind multiple turns through them, but are often sold for use as a string
> of beads on coax.
>
> How many beads are in the 8232? Are they Fair-Rite #73?
>
> 73, Jim K9YC
>
> On 12/9/2018 5:33 AM, Bob McGraw K4TAX wrote:
> > Balun Designs, both 1:1 and 4:1 for use with tuners.    I have both because I also have a folded dipole that I feed direct.
> >
> > I suggest you give the folks at Balun Designs a call and discuss your exact needs.  Take their advice.
> > Also see the DJ0IP site for details on baluns.  Just Google DJ0IP.
> >
> > And I use the 8232 common mode choke from The Wireman.
>

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