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| DIY CB UHF Antenna (Moxon) |
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Posted by: chucky504 - 27-07-2009, 11:03 PM - Forum: PROJECT AREA
- Replies (17)
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MOXON ANTENNA for CB
part1
MOXON RECTANGLE PROJECT FOR 477MHZ
This antenna is called a Moxon Rectangle, invented by an amateur, Les Moxon, G6XN. But this project is about CB, so we will use this design to make a moxon for 477 mhz cb. These can be made very lightweight, and the dimensions are smaller than a standard dipole. This means that you can fit one to a 5 watt handheld, with a little improvisation, or use it as a "stealth antenna" for noticeable improvement in TX/RX performance. And it's directional, so you get more of your ERP (effective radiated power) in the desired TX/RX direction.
The one I made worked well coupled to my GME tx7200, with a SWR of 1.5:1
The moxon is like a 2 element Yagi, or beam if you prefer, with the ends folded and critically spaced. This, if done accurately will eliminate the need for an impedance match. It's natural impedance will be around 50ohms, same as your radio. It is claimed by the QSY society (a bunch of Hams) that an accurately constructed moxon can give 7-14 dBi gain, with high front to back ratio. I have not verified this, but it does work better than a rubber duck!
Materials needed:
-Some thick copper wire, or brass welding rods, about 2- 3mm thick. a couple of coat hangers will even do.
-An insulating material for the spacers. The spacers hold the antenna together, and maintain the spacing between the ends of the driven elements and the ends of the reflector, at "C". Here we will use sections of an old fibreglass whip, But you could use chopsticks.Thats right, bamboo or plastic will do. Or something similar with electrically insulating properties. This will keep the antenna rigid and lightweight.
-Some cable ties. Small ones will do. Cop sized ones are too big.
-Some electrical tape to help hold things in place.
-Some coax with a connector on one end that suits your radio. Dont worry about the other end yet, This end will attach to the feedpoint. Simply split the coax and clamp, use crimp connectors, or solder the braid to one element and the core to the other. You should waterproof the feedpoint where the coax is split. I use hot melt glue smeared around with a paddle pop stick. It hardens up again in minutes, and you're ready to go. Face your 'favourite' repeater and go for it. If you have done a reasonable job and your radio has a signal strength meter you should notice an improvement over a rubber duck.
*NOTE: You will have to snip about 2.5mm off the end of each feedpoint to allow room for attachment of the coax. This will not affect the performance.
HANDY HINTS
Try to be as accurate as you can with measuring and bending. The better a Right Angle, 90deg, the better this thing works. Make sure at "C" the ends of the wire where they face each other are as square as possible. Side cutters leave a bit of a point, so allow a little extra and then file back
![[Image: 1_28_07_09_12_01_40.jpeg]](http://goldcoastcb.x10host.com/gallery/1_28_07_09_12_01_40.jpeg)
A Moxon can be made for any band.
A=213mm
B=32mm
C=5mm
D=45mm
E=B+C+D
![[Image: 20_27_07_09_10_45_12.jpeg]](http://goldcoastcb.x10host.com/gallery/20_27_07_09_10_45_12.jpeg)
The spacers are made of an old mobile whip, using the fibreglass stick.
![[Image: 20_27_07_09_10_47_25.jpeg]](http://goldcoastcb.x10host.com/gallery/20_27_07_09_10_47_25.jpeg)
Make sure "C" is spaced at 5mm. Now you can heat the shrink tubing.
![[Image: 20_27_07_09_10_51_04.jpeg]](http://goldcoastcb.x10host.com/gallery/20_27_07_09_10_51_04.jpeg)
You can use various ways to attach the spacers, as long as the method has electrically insulating properties
The remaining length of fibreglass whip was used as a little mast, to mount the Moxon. The reflector (the long unbroken side) was simply cable tied to one end of the whip. The other end of the whip was just strapped to the hand held.
If you plan to mount this antenna to the side of a metal pole, you must use a non-metallic horizontal stand-off boom. Or shove a piece of wooden broom handle or PVC into the end of the pole and attach the antenna reflector to that. Close proximity of other metallic structures will affect this antennas performance, so try to give it a little space.
![[Image: 20_28_07_09_12_02_48.jpeg]](http://goldcoastcb.x10host.com/gallery/20_28_07_09_12_02_48.jpeg)
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:icon_cat:good to hear you back on cOOter was on hand held tonight use for sandbaging but had to try to say hello geting beam soon I get a set for base this week speak soon good on ya :blob10: :blob10:
LOL 
![[Image: 1_23_07_09_9_50_38.jpeg]](http://www.goldcoastcb.com/forum/gallery/1_23_07_09_9_50_38.jpeg)
![[Image: 1_23_07_09_9_48_20.jpeg]](http://www.goldcoastcb.com/forum/gallery/1_23_07_09_9_48_20.jpeg)
![[Image: 1_23_07_09_9_49_17.jpeg]](http://www.goldcoastcb.com/forum/gallery/1_23_07_09_9_49_17.jpeg)
![[Image: 1_23_07_09_10_53_03.jpeg]](http://www.goldcoastcb.com/forum/gallery/1_23_07_09_10_53_03.jpeg)
![[Image: 1_23_07_09_9_50_16.jpeg]](http://www.goldcoastcb.com/forum/gallery/1_23_07_09_9_50_16.jpeg)
![[Image: top_lowlong_logo.gif]](http://www.australiamatters.com/images/top_lowlong_logo.gif){kind=logo}
Iv never heard him have one since iv been on radio, i was wondering when the day will be that deep Southern end users would benefit from repeater location and now it has finally happened for the southerners!! :headbang: Good stuff and channel 8 rules 
I came back from talking to Chris on pc server and ppl were yelling 
I tried to ask Emma a Question, i still dont know wat her answer was cause she was stomped!! 
????????????????????????????????????
Want to get into repeaters better with your Hand Held? If you have a handheld that has a detachable antenna, you're in business with a portable compact GAIN antenna with directional properties that you can build with simple materials. Having an antenna with Gain is like increasing your TX power......... NO 
this works, I made one :icon_geek:
please can you make a "technical" page to move this to? 
]
