144 MHz Omnidirectional Horizontal Antennas - Part
3
NEC Model Comparisons of Stacked Halo, Turnstile
and Eggbeater Omnidirectional Horizontally Polarized
Antennas for 144 MHz
by Dr. Carol F. Milazzo, KP4MD (posted 05 January 2013)
E-mail: [email protected]
INTRODUCTION
The halo, turnstile, eggbeater and Big Wheel are
omnidirectional horizontally polarized antennas used for
weak signal VHF terrestrial communications. Cebik3
duly described the benefits and problems of each of
these antenna designs. These antennas can be
stacked to increase gain at low elevation angles and to
decrease sensitivity to noise from high elevation
angles.
This study uses NEC modeling to compare the expected
performance of stacked pairs of each of these antenna
designs. The antennas were modeled with 4nec2 at 0.5λ
and 1λ above a simulated ground with spacing optimized
for minimum gain at 90º elevation and maximum gain
at 15º elevation.
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- Single
Halo,
Turnstile and Eggbeater at 0.5λ NEC Models
- Single
Halo,
Turnstile and Eggbeater at 1.0λ NEC Models
- Stacked
Halo,
Turnstile and Eggbeater Antenna NEC Models
- Single
Turnstile,
Triangle and Wheel at 0.5λ NEC Models
- Single
Turnstile,
Triangle and Wheel at 1.0λ NEC Models
- Stacked
Turnstile,
Triangle and Wheel Antenna NEC Models
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1. 144 MHz 2 stacked Halo Antennas horizontal
polarization radiation pattern calculated by NEC Model.
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2. 144 MHz 2 stacked Turnstile Antennas horizontal
polarization radiation pattern calculated by NEC Model.
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3. 144 MHz 2 stacked Eggbeater Antennas horizontal
polarization radiation pattern calculated by NEC Model.
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4. 144 MHz 2 stacked Halo Antennas vertical
polarization radiation pattern calculated by NEC Model.
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5. 144 MHz 2 stacked Turnstile Antennas vertical
polarization radiation pattern calculated by NEC Model.
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6. 144 MHz 2 stacked Eggbeater Antennas vertical
polarization radiation pattern calculated by NEC Model.
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7. 144 MHz 2 stacked Halo Antennas azimuth pattern
calculated by NEC Model.
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8. 144 MHz 2 stacked Turnstile Antennas azimuth pattern
calculated by NEC Model.
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9. 144 MHz 2 stacked Eggbeater Antennas azimuth pattern
calculated by NEC Model.
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10. 144 MHz 2 stacked Halo Antennas elevation pattern
calculated by NEC Model.
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11. 144 MHz 2 stacked Turnstile Antennas elevation
pattern calculated by NEC Model.
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12. 144 MHz 2 stacked Eggbeater Antennas elevation
pattern calculated by NEC Model.
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13. 144 MHz 2 stacked Halo Antennas 4nec2 Calculations.
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14. 144 MHz 2 stacked Turnstile Antennas 4nec2
Calculations.
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15. 144 MHz 2 stacked Eggbeater Antennas 4nec2
Calculations.
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CM 144 MHz 2 Stacked Halo Antennas at 0.5
and 1.0 lambda NEC model by Carol F. Milazzo, KP4MD
CM Horizontal orientation (using GH command)
CM Frequency = 145.000 MHz
CM 26-side polygon (40 inch loop with 1.5 inch gap)
CM Simulated good ground
CM http://www.qsl.net/kp4md/omnihoriz.htm
CE
SY frq=145 'Input frequency MHz
SY cir=40.21493 'Input loop
circumference inches (loop + gap)
SY r=0.5*cir/3.1415926 'Calculate
loop radius
SY dia=0.25 'Input loop wire dia.
inches
SY rad=0.5*dia 'Calculate loop
wire radius
SY n=26 'Input n-side polygon of
loop + gap
SY h=40.87 'Input height inches to
0.5 lambda
SY g=1.5 'Input gap size in inches
SY gseg=int(n*g/cir+0.5)
'Calculate gap length in segments
GH 1
n-gseg 1e-300
1e-300*(n-gseg)/n
r r
r r
rad 'First loop
GM 0
0 0
0 gseg*180/n
0 0
h 1 'Raise loop
to 0.5 lambda
GM 1
1 0
0 0
0 0
h 1 'Copy to
second loop at 1 lambda
GS 0
0 0.0254
GE 1
LD 5
0 0
0 58000000 '0.25
inch copper tubing
GN 2
0 0
0 4 0.01
EK
EX 0
1 (n-gseg)/2
0 0.5
0 0 'Feed point
EX 0
2 (n-gseg)/2
0 0.5
0 0 'Feed point
FR 0
0 0
0 frq 0
EN
16. 144 MHz 2 stacked Halo Antennas NEC model.
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CM 144 MHz Stacked Turnstile Antenna NEC
model by Carol F. Milazzo, KP4MD
CM Horizontal orientation
CM Frequency = 145.000 MHz
CM 21 segments per dipole
CM Simulated good ground
CM http://www.qsl.net/kp4md/omnihoriz.htm
CE
SY frq=145 'Input frequency MHz
SY len=39.815 'Input dipole length
inches
SY dia=0.25 'Input dipole dia.
inches
SY rad=0.5*dia 'Calculate dipole
radius
SY n=21 'Input segments per dipole
(must be odd)
SY nc=0.5*(n+1) 'Calculate feed
point segment
SY h=40.87 'Input height inches to
0.5 lambda
SY s=0.25 'Input separation
between each dipole in pair inches
GW 1
n 0
-len/2 h
0 len/2
h rad 'First
dipole at 0.5 lambda
GM 1
1 0
0 90
0 0
s 1 'Rotate to
form second dipole at right angle
GM 2
1 0
0 0
0 0
h 1 'Copy dipole
pair to 1.0 lambda
GS 0
0 0.0254
GE 1
LD 5
0 0
0 58000000 '0.25
inch copper tubing
GN 2
0 0
0 4 0.01
EK
EX 0
1 nc
0 0
1 0 'Feed point
EX 0
2 nc
0 -1
0 0 'Feed point
EX 0
3 nc
0 0
1 0 'Feed point
EX 0
4 nc
0 -1
0 0 'Feed point
FR 0
0 0
0 frq 0
RP 0
1 361
1000 76.
0. 0.
1. 0.
EN
17. 144 MHz 2 stacked Turnstile Antennas NEC model.
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CM 144 MHz Stacked Eggbeater Antenna NEC
model by Carol F. Milazzo, KP4MD
CM Vertical orientation (using GH command)
CM Frequency = 145.000 MHz
CM 42-side polygon loops
CM Simulated good ground
CM http://www.qsl.net/kp4md/omnihoriz.htm
CE
SY frq=145 'Input frequency MHz
SY d=29.01591 'Input loop diameter
inches
SY r=0.5*d 'Calculate loop radius
SY dia=0.5 'Input loop wire dia.
inches
SY rad=0.5*dia 'Calculate loop
wire radius
SY n=42 'Input n-polygon loop
SY h=40.66136 'Input height inches
to 0.5 lambda
GH 1
n 1e-300
1e-300 r
r r
r rad 'Form
first loop in ground
GM 0
0 90
90-180/n 0
0 0
h 0 'Raise loop
center to 0.5 lambda and rotate to orient vertically
GM 1
1 0
0 90
0 0
.25 1 'Rotate
loop 90 degrees to form second loop
GM 2
1 0
0 0
0 0
h 1 'Copy to
second set of loops at 1.0 lambda
GS 0
0 0.0254
GE 1
LD 5
0 0
0 58000000 '0.5
inch copper tubing
GN 2
0 0
0 4 0.01
EK
EX 0
1 n
0 0
1 0 'Feed point
EX 0
2 n
0 -1
0 0 'Feed point
EX 0
3 n
0 0
1 0 'Feed point
EX 0
4 n
0 -1
0 0 'Feed point
FR 0
0 0
0 frq 0
EN
18. 144 MHz 2 stacked Eggbeater Antennas NEC model.
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RESULTS
- All antennas had maximum lobe gains between 6.8 and
7.9 dBi of each other at 15º elevation.
- The turnstile and eggbeater antennas more closely
approximated an omnidirectional pattern with 0.7-1.0
dB variation in azimuth radiation while the halo
antenna exhibited a 3.1 dB differential in gain
between its major and minor axes.
- All antenna types showed similar elevation radiation
patterns with nulls of -20 dBi or lower toward the
zenith.
- The turnstile antenna exhibited the
least suppression of vertically polarized noise.
CONCLUSION
Although the overall expected performance of each of
the models is similar, the following differences should
be considered:
- The difference in performance may not warrant
incurring the greater construction complexity of any
particular antenna design.
- The losses incurred in the additional stacking and
phasing harnesses may diminish or negate the expected
gain in any particular antenna design.
- Deviations in the antenna and phasing harness
dimensions can significantly skew the radiation
patterns.3
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19. Composite of all 144 MHz 2 stacked Antennas azimuth
patterns - horizontal polarization component only.
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20. Composite of all 144 MHz 2 stacked Antennas azimuth
patterns - vertical polarization component only.
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REFERENCES
- The
HO Collinear, A Horizontal Omni, Anderson R,
W1HBQ
- The
Double Turnstile Antenna, Beech J, G8SEQ
- Horizontally
Polarized Omni-Directional Antennas: Some Compact
Choices, Part 1, Cebik, LB, W4RNL
- Horizontally
Polarized Omni-Directional Antennas: Some Compact
Choices, Part 2, Cebik, LB, W4RNL
- Experimental
Omnidirectional Antennas for 6-Meters, Cebik,
LB, W4RNL
- 144 MHz Halo Antenna,
Milazzo C, KP4MD
APPENDIX: NEC MODEL FILES
- 144
MHz 2 Stacked Halo Antennas NEC Model
- 144 MHz 2
Stacked Turnstile Antennas NEC Model
- 144 MHz 2
Stacked Eggbeater Antennas NEC Model
LINKS
- Single Halo,
Turnstile and Eggbeater at 0.5λ NEC Models
- Single
Halo, Turnstile and Eggbeater at 1.0λ NEC Models
- Stacked
Halo, Turnstile and Eggbeater Antenna NEC Models
- Single
Turnstile, Triangle and Wheel at 0.5λ NEC Models
- Single
Turnstile, Triangle and Wheel at 1.0λ NEC Models
- Stacked
Turnstile, Triangle and Wheel Antenna NEC Models
- Omnidirectional
Horizontal
Antenna Photo Album
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21. Composite of all 144 MHz 2 stacked Antennas
elevation patterns - horizontal polarization component
only.
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22. Composite of all 144 MHz 2 stacked Antennas
elevation patterns - vertical polarization component
only.
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