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2M Moxon Antenna

2M Moxon Antenna. 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. Moxon cont’d.

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2M Moxon Antenna

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

  15. 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. gain @ 12º (can be changed in the program). Elevation Plot

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

  17. 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

  23. Bill of Materials Web Site http://www.moxonantennaproject.com/

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