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4NEC2 models

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4Nec-2 is driving me nuts. I cannot figure out how to model a phase shifted antenna. I wanted to model a turnstile antenna with a reflector for 1280MHz. I can't seem to figure out how to get it to figure a 90 degree phase shift stub. I can use two separate sources, but then the program only recognizes the one source and ignores the second.

I am working on a few circularly polarized antenna designs: the cloverleaf antenna and a reflected turnstile antenna. For the turnstile I think I need to mount the reflector .2-.25 wavelengths away from the center of the antenna for what I hope is about 5 dbi gain. Unfortunately I can't seem to model it to verify this.

I am also trying to develop 2 new antenna designs, the bluppnik and the Caltrop. Both require a 90 degree stub. I hope to achieve omni directional circular polarization with these antennas. I have the 4NEC-2 file for the turnstile, but obviously still haven't figured out the phase shift issue. I think circular polarization is the way to go for FPV projects, I just wish I could model the antennas before I build them.

Any help?

Thanks,

-Alex

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This is the 4NEC-2 file I can't get to recognize the second voltage source. I have it for 910MHz:

CE

SY w1seg=5, w1x1=3.125, w1y1=0, w1rad=0.0394

GW 1 w1seg -w1x1 w1y1 w1y1 w1x1 w1y1 w1y1 w1rad

SY w2y1=3, w2z1=0.2

GW 2 w1seg w1y1 -w2y1 w2z1 w1y1 w2y1 w2z1 w1rad

GS 0 0 0.0254 ' All in in.

GE 0

EX 0 1 3 0 1 0

GN -1

SY Freq=910

FR 0 1 0 0 Freq

post-6287-0-76767800-1294320375_thumb.jp

post-6287-0-89166500-1294320387_thumb.jp

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Good to see you here Alex, sad to say I cant help, I did make a turnstyle aerial for 2.4Ghz using a quadrature? I think it was called but never found much need for it. I also made a helical which worked very well but again for the type of missions I fly vertical polarization seems to be the best. Always interested to what others are doing though ;)

Terry

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The helical has been a pain for me. I can't get the VSWR below 2:1... I have had great luck with the skew planar wheel, though.

I am trying to develop a few different circular antennas. Sure I could copy a circular patch, deal with the 2:1 VSWR of the helical, fly the skew planar wheel and call it a day, but that's not my style. I want to improve my head mounted base station. I just want to get 3/4 mile out of it reliably. I think a turnstile with a reflector will do that... maybe. There's also the cloverleaf, as well as a new antenna of my own design.

I have also been considering a turnstile made from two loop dipole antennas to give me a little bit better control of VSWR in regards to hitting the desired bandwidth, but making 3 baluns would be a royal pain...

-Alex

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I looked through my RF books, NEC files, and checked the ARRL database. But unfortunately I can't find anything to help with your modeling issue. Would be interesting to see an accurate 4nec2 file for the turnstile, so please keep us posted.

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I'm working on it, still. I have a bunch of other CP designs I plan to try. I have been sending my antennas to Florida for testing.

I just purchased the ARRL antenna book. You know you are a geek when you anticipate an antenna text book in the mail :)

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For the last week I've been trying to define a PinWheel antenna in 4Nec2 with variables that allow it to be optimized by the program. It was certainly one of the most difficult antennas to model but it is finally done. Here is a little video showing how the program converges toward an optimization balancing SWR, Gain (at zero elevation) and axial ratio (best multipath performance):

SPoptimizePlay.jpg

Note that this is for a 1280 Mhz antenna and that the optimized result was:

Leg Length = 67.14 mm

Arc Angle = 81.8 degrees

Arc Length = 121.5 mm

Pitch = 47.1 degrees

(this was for a 0.6 mm dia magnet wire)

For those of you that know how to run 4nec2x, here is the file:

http://www.af9y.com/PINWHEEL52.NEC

OMM

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