1. 2M Moxon Antenna

2. Moxon Antenna Moxon antenna is a 2 element reduced size antenna.
The Elements are bent (reducing the size)
It has similar characteristics as a 3 element yagi.
It has a large beam width and very good Front-to-Back ratio.

3. Moxon cont’d
Use Moxon Generator (freeware) to calculate the size of the antenna.
Insert the dimensions into a Antenna Modeling program. (Most of the diagrams are from cocoaNEC – MAC program)
Determine the characteristics of the antenna from the model.
Can be horizontal or vertical polarization.

4. Moxon Designer for the Mac computer
(Freeware )

5. Moxon Generator for Windows
It will automatically generate a model in EZNEC format.
(Freeware)

6. 3 6
Wire # 5 2
Denotes Feedpoint
0, 0, 10’ 1 4

7. Antenna Modeling
Most Antenna Modeling programs use NEC 2 (freeware) or NEC 4 (commercial).
The Antenna Modeling program is the interface to and from the NEC computational engine. It makes it easier to understand.
You describe the antenna using wires (this could be tubing). This is the most tedious part.

8. Antenna Modeling cont’d
You have to designate on which wire the feed point is located.
You select type of ground, and other things related to the antenna, number of segments.
The model will generate Azimuth, Elevation, SWR, other curves and information.
You can then change the model to get the best patterns/SWR etc.

9. Antenna Modeling cont’d
There are limitations to the models on certain items (it will not do under ground radials – you have to fudge them).
If you stay within the limitations of the program, it will model the antenna correctly.
Use modeling to build better antennas.
Antenna modeling programs for amateurs can be freeware or cost up to ~ $ 200.

10. Antenna Modeling cont’d
The one that is used most by hams is EZNEC. The current version is 5, and costs $ 89. It has several different versions with different features. EZNEC 5 is for an antenna with 500 or less segments.
EZNEC has a demo version with a limitation of 20 segments (can model a dipole).

11. Antenna Modeling cont’d
Each modeling program has advantages & disadvantages.
EZNEC is the most widely used for amateurs – so getting models from other amateurs is easier.
Do a Google search for address.
Freeware Antenna Modeling program – do a search for 4nec2.

12. Antenna Modeling cont’d
The gain shown in the model is dBi – this is the gain over an Isotropic antenna (one out in free space – don’t exist [theoretical antenna]).
Some programs will give it in dBd – gain over a ½ wave dipole.
To go from dBi to dBd you subtract 2.1 dB.
5.6 dBi = ~ 3.5 dBd.

13. Antenna Modeling cont’d
Information that is nice to know about a Yagi:
Beam Width
Elevation Angle
Front to Back Ratio
Antenna Pattern
Gain
SWR
Bandwidth (range of frequency < SWR 2:1)

14. Azimuth Plot – different frequencies
Outside Ring = 6.27 dBi
Beam Width
Angle where signal is down 3 dB
~ 125 degrees
Design Freq.
Azimuth Plot – different frequencies

15. Elevation Angle – Main Lobe angle ~ 12 deg.
Outer Ring = 8.65 dBI
Elevation Angle – Main Lobe angle ~ 12 deg.
Front-to-Back
~ 18 dB
- 16 dB
- 20 dB
Notice the outer circles for the Azimuth & Elevation do not match. The reason for this is that the Azimuth plot is the signal at 20º - max. 12º (can be changed in the program).
Elevation Plot

16. Smith Chart – shows antenna impedance at different frequencies
SWR 2:1 Circle
Center of Chart
50 ohms resistive
SWR 3:1 Circle
Smith Chart – shows antenna impedance at different frequencies

17. (not exactly the same model)
EZNEC 5 SWR Plot
(not exactly the same model)

18. Effects on Antennas
The ground effects antennas. If you are a 1λ above ground it almost no effect. (Practically if you are ½ λ – little effect – on 2M ~ 6’). Antenna Models model different types of Grounds (so you can get more realistic results).
Diameter of the elements.
Distance from antenna to other objects.

19. Building Moxon Antennas
The measurements are the same (assuming the same freq. etc.) – how it is constructed can be totally different.
For the 2M Moxon, I use ½” PVC pipe & fittings and #8 bare copper wire.
These materials can be purchased at Home Depot for under $ 15. (Lowes only carries #6 bare copper wire – changes sizes slightly.)

20. Building Moxons cont’d
I use PVC pipe because it is cheap (the watch word for amateur radio) and readily available.
The #8 wire is stiff enough to keep it’s shape (pretty cheap and is available).
I made a 10M Moxon using # 14 AWG wire.
Some hams build them with aluminum tubing.

21. D C B A
Reflector
Driven Element

22. D C B A
Reflector
Driven Element
Direction of Radiation

24. Bill of Materials
Qty.
Description 4
6 X 32 5/8” Brass Screws
36”
½” PVC Sch. 40 Pipe 2
½” PVC Tees 1
½” PVC Cross
½” PVC Plugs 8’
#8 AWG Bare Copper Wire
RG-8X or RG-58
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