[amsat-bb] Modeling the AA2TX Parasitic Lindenblad

Sat Jul 11 00:43:00 UTC 2020

Hi Zach,

My intuition is that the relatively small change in the diameter of the
radiating element, and material change, will not significantly change the
performance of the paralindy antenna.

Increasing the diameter of radiating dipole elements has the effect of
broadening an SWR curve, providing more usable bandwidth. Consider a
75-meter dipole comprised of one wire, then increase it's effective
diameter by replacing it with a "caged dipole" of four wires separated by a
foot or so.

http://www.arrl.org/files/file/Technology/pdf/The%20Cage%20is%20Back%20W1AW.pdf

Furthermore, the change in diameter you're proposing (0.1 in) is a very
small fraction of the design wavelength -- so I wouldn't expect to see any
significant broadening of the performance vs frequency.

My intuition is guided by a couple of semesters of E&M and a few decades of
antenna building and testing.  BUT it's only my *intuition*, and I'd be
very interested in hearing the results of any modeling!

As an aside, I'm also working to build this antenna with my newly-acquired
3D printer, using PETG in fact!  I'm redesigning the 70-cm Lindy as well as
2-m Lindy to use arrow shaft elements.  In this manner the antenna will be
easy to disassemble and easily portablized.  Or transported  :)

Curt / K7ZOO

On Fri, Jul 10, 2020 at 4:45 PM Michelle Thompson via AMSAT-BB <
amsat-bb at amsat.org> wrote:

> Would HFSS help?
>
> If you have a sketch, then I have someone that can model it at no cost.
>
> -Michelle W5NYV
>
>
>
>
> On Fri, Jul 10, 2020 at 4:05 PM Zach Metzinger via AMSAT-BB <
> amsat-bb at amsat.org> wrote:
>
> >
> > Hello folks,
> >
> > I've been intrigued by Tony's Parasitic Lindenblad ever since I first
> > read about it. I have a center section in CAD, suitable for 3D printing
> > in PET-G, which eliminates the messy gluing, etc. and gives me a chance
> > to use my printer. :-)
> >
> > However, I'd like to eliminate the requirement for the 0.750" OD
> > aluminum mast and replace it with 0.650" OD (name: 1/2") copper water
> > pipe, which can be readily found in any hardware store. Given the
> > appropriate paint coating, copper pipe has held up well over many years
> > at my QTH when exposed to the elements.
> >
> > I am using Xnec2c on FreeBSD, but any NEC program should be able to use
> > the deck, to model the antenna. However, my dimensions don't seem to
> > match what Tony came up with. Are there any NEC gurus in the audience?
> >
> > Here's my sophomore stab at the antenna deck:
> >
> > CM --- NEC2 Input File created or edited by xnec2c 3.4 ---
> > CM AA2TX Parasitic Lindenblad -- All distances in meters
> > CM Goal is to use 1/2" copper water pipe for dipole element (0.650" OD)
> > instead of 3/4" OD aluminum pole
> > CE --- End Comments ---
> > GW     1    15   0.00000E+00  0.00000E+00 -1.39000E-01  0.00000E+00
> > 0.00000E+00  1.39000E-01  1.58750E-02
> > GW     2    15   2.58000E-01  8.50000E-02  1.49000E-01 -2.58000E-01
> > 8.50000E-02 -1.49000E-01  1.50000E-03
> > GW     3    15  -2.58000E-01 -8.50000E-02  1.49000E-01  2.58000E-01
> > -8.50000E-02 -1.49000E-01  1.50000E-03
> > GW     4    15   8.50000E-02  2.58000E-01 -1.49000E-01  8.50000E-02
> > -2.58000E-01  1.49000E-01  1.50000E-03
> > GW     5    15  -8.50000E-02  2.58000E-01  1.49000E-01 -8.50000E-02
> > -2.58000E-01 -1.49000E-01  1.50000E-03
> > GE     0     0   0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
> > 0.00000E+00  0.00000E+00  0.00000E+00
> > EX     0     1     8      0  1.00000E+00  0.00000E+00  0.00000E+00
> > 0.00000E+00  0.00000E+00  0.00000E+00
> > FR     0    20     0      0  4.30000E+02  1.00000E+00  0.00000E+00
> > 0.00000E+00  0.00000E+00  0.00000E+00
> > NH     0     0     0      0  0.00000E+00  0.00000E+00  0.00000E+00
> > 0.00000E+00  0.00000E+00  0.00000E+00
> > NE     0    10     1     10 -1.35000E+00  0.00000E+00 -1.35000E+00
> > 3.00000E-01  0.00000E+00  3.00000E-01
> > RP     0    19    37   1000  0.00000E+00  0.00000E+00  1.00000E+01
> > 1.00000E+01  0.00000E+00  0.00000E+00
> > EN     0     0     0      0  0.00000E+00  0.00000E+00  0.00000E+00
> > 0.00000E+00  0.00000E+00  0.00000E+00
> >
> > Questions that arise from an afternoon of fiddling with this:
> >
> > 1) Should I model the driven element as two wires with the 1/4" gap
> > between them? If so, how would I do this?
> >
> > 2) Will the 0.100" difference in OD make enough of a difference to even
> > go through this exercise?
> >
> > Any and all comments, especially from NEC gurus, appreciated!
> >
> > --- Zach
> > N0ZGO
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> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership. Opinions
> expressed
> are solely those of the author, and do not reflect the official views of
> AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb
>