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4NEC Model of droopy 1/4 problems Jun 16th 2015, 23:18 5 1,731 on 17/6/15

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4NEC Model of droopy 1/4 problems KK6QHZ on 17/6/15
For my on sanity I reset the starting values to the conventional values and ran the optimization again. This time it converged near the expected values. I compared the results (SWR, Gain, Z) of the two sets of values and they quite similar.

I can come up with several reasons why something like this could happen but have no clue as to which it might me. I will play around a bit more for my own education but conventional beats wierd results every time (-;

Thanks for the conversation Zack and 73's.


4NEC Model of droopy 1/4 problems KK6QHZ on 17/6/15
The lengths are in meters and 5/8 wavelength would be somewhere between 1.2 and 1.3 meters. (Your idea does raise the question of could a 5/8 wave work?)

By my calculations, 0.6165 meters is about 3/10 of a wavelength. With these numbers in mind, I'm not sure that the 5/8 theory is the solution.

Since I am new to 4NEC2, the problem could easily lie with how I modeled the antenna.

Thanks for the idea Zack.

4NEC Model of droopy 1/4 problems KK6QHZ on 16/6/15
I was decided I to put a 2 meter antenna in my attic for use with my hand held and after browsing the web, decided a 1/4 wave "droopy" with 4 radials might be a good choice.

Conventional wisdom is that the vertical should be slightly less than 1/4 wave. The radials should be a 1/4 wave and angled down at 45 degrees for impedance matching. It seemed like an educational venture to model the antenna with 4NEC2 to learn about antenna modeling. My optimized results do not agree with conventional wisdom and I am stumped as to why. Below are setup info, results and the card deck for NEC.

Suggestions appreciated and thanks in advance.


4NEC2 version 5.8.15

Optimization settings
All others 0
Freq 146

0.6165 = Monopole length - Optimized
0.1993 = Radial length - Optimized
30.0 = Radial droop angle - Optimized
3.1 = Antenna height - estimated height in attic from true ground

From 144 to 148Mhz

SWR < 1.25
Gain essentially 4.7
Z 46 to 52 ohms

NEC card deck

CM 2 Meter 1/4 wave
CM 4 radial drooping
SY high=3.1 'Antenna height
SY wlen=0.6165 'Monopole length
SY rlen=0.1993 'Radial length
SY droop=30.0 'Radial droop angle
SY drpang=cos(droop) 'Adjustment for droop
SY r1x=rlen*1.0*drpang 'Radial 1 X
SY r1y=rlen*0.0*drpang 'Radial 1 Y
SY r2x=rlen*-1.0*drpang 'Radial 2 X
SY r2y=rlen*0.0*drpang 'Radial 2 Y
SY r3x=rlen*0.0*drpang 'Radial 3 X
SY r3y=rlen*1.0*drpang 'Radial 3 Y
SY r4x=rlen*0.0*drpang 'Radial 4 X
SY r4y=rlen*-1.0*drpang 'Radial 4 Y
SY rz=high-(sin(droop)*rlen)
GW 1 32 0 0 high 0 0 wlen+high 2.588mm 'Monopole
GW 2 16 0 0 high r1x r1y rz 2.588mm 'Radial 1
GW 3 16 0 0 high r2x r2y rz 2.588mm 'Radial 2
GW 4 16 0 0 high r3x r3y rz 2.588mm 'Radial 3
GW 5 16 0 0 high r4x r4y rz 2.588mm 'Radial 4
GE 1
GN 0 0 0 0 5 0.001
EX 0 1 1 0 1 0 0 'Voltage source (1+j0) at wire 1 segment 1.
FR 0 0 0 0 146 0

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