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Author Topic: DIY CB UHF Antenna (Moxon)  (Read 11678 times)
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chucky504
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« on: July 27, 2009, 11:03:34 PM »

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



A Moxon can be made for any band.
A=213mm
B=32mm
C=5mm
D=45mm
E=B+C+D

The spacers are made of an old mobile whip, using the fibreglass stick.



Make sure "C" is spaced at 5mm. Now you can heat the shrink tubing.



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.
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King_DaVo
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« Reply #1 on: July 27, 2009, 11:28:38 PM »

Awesome,  was working really well too  thumbsup   hehehee     Good shit Chucky, well done.   

violent5
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Reply #1 on: July 27, 2009, 11:28:38 PM

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cOOter
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!!! disco chicken !!!


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« Reply #2 on: July 28, 2009, 10:22:38 AM »

 director MOXON ROCKS ON!!!   occasion18

Chucky left one moxon here for a 5watt uniden I use downstairs for sand bagging. I say sandbagging because I could only just pick channel 08 up, let alone talk on it.  tard

Poked the moxon out the downstairs window, and guess what, the bloody thing works.  tongue1

Ow Chucky, you do it again  icon_thumright  coffee2
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chucky504
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« Reply #3 on: July 28, 2009, 11:57:13 AM »

 director  COMING SOON, MOXON PART 2: STACKED MOXONS

 :read: book1 Research is underway for a stacked pair. I got other stuff going on, so this will take a little time. Hope you enjoyed part one.
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Reply #3 on: July 28, 2009, 11:57:13 AM

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King_DaVo
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« Reply #4 on: July 28, 2009, 05:03:31 PM »

Keep em Coming Chuckster!!   thumbsup

 icon_king
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chucky504
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« Reply #5 on: August 02, 2009, 12:23:10 AM »

Research shows that there is not much to be gained by stacking moxons. Moxons are OK, and work well according to feedback, but if you want more gain and directivity you need to go for a multi element type of antenna.

QUADS are awesome by the way. A little more complicated to build though.
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Reply #5 on: August 02, 2009, 12:23:10 AM

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cOOter
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« Reply #6 on: August 02, 2009, 10:02:12 AM »

I just noticed from a  newbie point of view, that we didn't add close up images of how the coax ajoins the aerial. If you up load a few picks that shows coax connected to the aerial, I'll size them and add 'em them into the project page.  thumbsup
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chucky504
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« Reply #7 on: August 02, 2009, 11:52:20 AM »

OK will take some pics and we can update the project
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King_DaVo
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« Reply #8 on: August 02, 2009, 02:56:34 PM »

Yeah do it,  oi get serious and do some QUADS up,   RF baby!!!    hello2

 laughing4
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chucky504
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« Reply #9 on: October 14, 2009, 01:48:18 AM »

Bandicoot is rockin VNR-08 with his new Moxon. Good one. Nice to make it yourself book1 and know it goes well.  violent5     Post a pic Bandicoot. aluminium is such a pretty metal
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BA15
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« Reply #10 on: November 19, 2009, 02:13:20 PM »

hay guys. newby here BA15 shane.  this moxon looks great. how do you think it will work set on a plastic conduct pipe with directors in front.
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cOOter
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« Reply #11 on: November 19, 2009, 08:16:49 PM »

hay guys. newby here BA15 shane.  this moxon looks great. how do you think it will work set on a plastic conduct pipe with directors in front.

Gday Shane, and welcome aboard.  occasion18

Chucky is the main man that has all the info on the MOXON.  book1


Helper Elf Chucky copy!!!  icon_smurf

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chucky
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« Reply #12 on: November 20, 2009, 12:15:11 AM »

Well you could try adding directors and see how it works, but I'm certain the impedance will be affected and then you'd have something resembling a Yagi/beam, which will go better. The Moxon is basically a  modified 2 ele beam, which is supposed to have more gain than a conventional 2 ele beam. So you get the most gain for the amount of elements. Moxons are good for certain applications such as portable setups, indoors, foldback receive antennas, improved handheld performance over a rubber ducky and situations requiring a small "stealth antenna" with big punch and directional qualities. I know a guy who lives on a mountain who has a good signal into VNR08 with a multi element beam. Trouble is, he also hits 08 in Oceanview,  off the back of the beam and they get pissed off. He solved the problem using a Moxon pointed at 08. icon_thumright

So you probably won't win any power battles with one, but they do have their uses and are so easy to build. If you want serious gain, contact Neighbour and get one of his yagis  thumbsup Good Luck
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BA15
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« Reply #13 on: November 20, 2009, 12:42:26 PM »

Well you could try adding directors and see how it works, but I'm certain the impedance will be affected and then you'd have something resembling a Yagi/beam, which will go better. The Moxon is basically a  modified 2 ele beam, which is supposed to have more gain than a conventional 2 ele beam. So you get the most gain for the amount of elements. Moxons are good for certain applications such as portable setups, indoors, foldback receive antennas, improved handheld performance over a rubber ducky and situations requiring a small "stealth antenna" with big punch and directional qualities. I know a guy who lives on a mountain who has a good signal into VNR08 with a multi element beam. Trouble is, he also hits 08 in Oceanview,  off the back of the beam and they get pissed off. He solved the problem using a Moxon pointed at 08. icon_thumright

So you probably won't win any power battles with one, but they do have their uses and are so easy to build. If you want serious gain, contact Neighbour and get one of his yagis  thumbsup Good Luck
  ok. i understand. iv been thinking about seting a 1/4 wave stainless whip on on boom with reflectors and directors in vertical polarisation to see if it will power up... or not... any thoughts
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bandicoot
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« Reply #14 on: November 21, 2009, 05:40:56 AM »

 director roger that pics posted in project gallery the mockon rocks on! :fish:
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