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146MHz
3 PETAL CLOVER LEAF ANTENNA
146MHz
3 Petal Cloverleaf
tower mounted antenna. September 2016
Requiring a horizontally polarised 2 metre band antenna for SSB (Single Side Band) work and also needing to develop a horizontally polarised omnidirectional
(HPOD) antenna for both the 2 metre band and 70 centre-metre
band for a proposed beacon site, I decided that a
3
Petal
Cloverleaf or sometimes referred to as a Big Wheeled antenna could be constructed as a robust unit that would be easily replicated and require little maintenance.
Construction
The antenna is constructed around a standard male N connector with a 100mm diameter aluminium radial mounting disk with a 15mm centre hole to attach to the N connector with the standard coax gland screw cap as shown in Figure
4 and Photos 2 ~ 7. The elements have been attached with 3mm diameter pop-rivets to the mounting disks
The smaller upper disk is fitted to a standard male N connector's coax centre pin and positioned in the N connector and secured with two part epoxy. A small rubber grommet has been fashioned to fit tightly in the end of the N connector body with a smearing of marine grade silicon to make to assembly water proof.
The antenna mounting is a standard antenna mirror mount bracket with a female to female N connector bulkhead socket fitted for a range of similar antennas that are constructed around male N connectors. See:
Generic Antenna Mount.
Photo 1 146MHz
3 Petal Cloverleaf assembled.
Figure 1 3
Petal Cloverleaf
general layout.
Figure 2 Cloverleaf element dimensions.
| SECTIONS |
FREQUENCY
MHz |
| 144.5 |
145.5 |
146.5 |
222 |
430 |
435 |
440 |
| mm |
mm |
mm |
mm |
mm |
mm |
mm |
| L1 |
398 |
395 |
392 |
252 |
121 |
119 |
118 |
| L2 |
417 |
414 |
411 |
271 |
140 |
138 |
137 |
| L3 |
161 |
160 |
159 |
105 |
54 |
54 |
53 |
| L4 |
908 |
902 |
896 |
591 |
305 |
302 |
298 |
| L5 |
161 |
160 |
159 |
105 |
54 |
54 |
53 |
| L6 |
408 |
405 |
402 |
262 |
131 |
129 |
128 |
| L7 |
417 |
414 |
411 |
271 |
140 |
138 |
137 |
| TOTAL
SECTION LENGTH |
2036 |
2022 |
2008 |
1316 |
666 |
658 |
650 |
| RAD
1 |
127 |
126 |
125 |
82 |
43 |
42 |
42 |
| RAD
2 |
127 |
126 |
125 |
82 |
43 |
42 |
42 |
| RAD
3 |
383 |
381 |
378 |
249 |
129 |
127 |
126 |
Figure 3 Cloverleaf element dimensions table.
Figure 4 Cloverleaf
antenna hub plates dimensions.
Figure 5 Cloverleaf hub
assembly with element attachment.
Figure
6
Cloverleaf
matching stub
 |
 |
| Photo 2
3
Petal Cloverleaf hub plates.
|
Photo 3
3
Petal Cloverleaf lower hub plate
assembled.
|
 |
 |
| Photo 4
3
Petal Cloverleaf lower hub plate
assembled.
|
Photo 5
3
Petal Cloverleaf upper hub plate
assembled.
|
 |
 |
| Photo 6
3
PetalCloverleaf hub plates assembled.
|
Photo 7 146.5MHz
3
Petal Cloverleaf
hub plates and matching stub. |
Antenna
testing
With the antenna assembled on an easily accessible test mast well clear of the ground and surrounding metallic objects, the antenna was connected to an AIM 4170C antenna analyser to ascertain how the antenna loaded up.
The goal here is to find the lowest SWR for the operating frequency of 146.5MHz and ideally have the resonant frequency as close as is possible to the same frequency
The AIM 4170C produces a display of all relevant data and most importantly it can project it's analysis to the antenna end of the coax giving a truer picture of the antenna.
With modest adjustment of the matching stub length an SWR of 1.7 was realised at 146.50MHz with a resonant frequency at 146.357MHz. The SWR was low across the full 2m band with only maximum of 2.0 at 144MHz. The phase angle shown in purple displays a shallow zero angle crossing at 146.357MHz indicating the resonant frequency of the antenna.
Figure 7 146MHz
Cloverleaf AIM
4170C antenna analyser plot.
.
AIM
4170C antenna analyser explanation;
| SWR |
Standing
Wave Ratio. |
| Zmag |
Total
Impedance. |
| Phase |
Phase
angle between voltage and current. |
Details
of the generic antenna mount. See: Generic Antenna
Mount.
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last revised 05 May, 2025
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