Hi Mike and Don
The DHDL as well as few other antennas, has a hidden component. The bottom
wire parallel to the ground is a transmission line, actually, any antenna
parallel to the ground is a transmission line. A beverage antenna a is
good example.
The ground is the second leg of the transition line, for a K9AY loop it is
the same, the bottom wire and the ground form a transmission line. The
transmission line allows the Resistor and the Transformer to be moved to the
center of the loop. The VE3DO loop is also exactly the same.
The same way, a DHDL antenna uses the ground to phase the two loops, if you
elevate the DHDL high far from the ground, the patter changes. The DHDL is a
ground dependent antenna, improving the ground with a ground wire bellow the
antenna can fix some ground problems.
My two cents.
73's
JC
N4IS
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Don Kirk
Sent: Sunday, December 11, 2016 10:13 AM
To: D Michael <damichael@verizon.net>
Cc: topband <topband@contesting.com>
Subject: Re: Topband: Twist a Flag into a Bowtie?
Hi Mike,
Funny you should ask that.
A few months ago (September) I was looking at building a smaller size DHDL
using 4Nec2, and there were a few things I saw that I thought needed
improvement (I saw things in the full size DHDL that I thought needed
improvement, it was not limited to the small size DHDL I was trying to
design). Then I started to play around with the location of its termination
resistor as well as routing of wires, and wound up with what I called the
Terminated Bowtie. I built one in my backyard but my yard is pretty small
and the antenna was too close to existing objects (house and chain link
fence) and I did not realize the S/N improvement that I expected,
nevertheless based on modeling it looks like a winner (9.5 RDF and front to
back ratio versus elevation angle very robust).
I have attached the preliminary document I put together a few months ago for
you and others to view (it might not be perfect, but should convey my design
/ thoughts). I would love someone to build one of these out in the open to
see if the real life build provides results similar to the 4Nec2 modelling I
did.
Note: Bringing the feedline away from the antenna properly needs to be
looked at to minimize distortion of the pattern. As I recall the feedline
should not drop down to the ground until it's at least 5 feet away from the
antenna, and a greater distance would be best. The feedline should also use
choke with ground rod similar to what's recommend for other RX antennas we
use (beverages, flags, etc.) to block common mode noise from making its way
to the antenna feedpoint.
Let me know what you think. It might not work, but sure looked good on
paper.
73,
Don (wd8dsb)
On Sun, Dec 11, 2016 at 9:41 AM, D Michael <damichael@verizon.net> wrote:
>
>
> I have two flag rx ants and I was looking at the DHDL and DK6ED Double
> Loop System V2 and wondering if twisting my Flag rx ants into Bowties
> would improve the forward pattern and make them narrower with better
> front to back.
> I would just ""flip"" the termination resistor end to form a loose
> BOWTIE shape.
> I have no ant modeling software so I have no way to ponder this change.
> Maybe someone could model doing this.
> TNX es 73, Mike W3TS
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|