Multi-Band Moxon Antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by OD5OJ, Nov 23, 2019.

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  1. OD5OJ

    OD5OJ Ham Member QRZ Page

    Hello All

    I am working on a new Multi-Band Moxon Antenna Project (10-12-15-17-20m). please find below-attached pic. I have read a few articles about feeding the elements and I was hoping if anyone had the opportunity to realize this project before or has any idea of feeding the antenna. some projects proposed a double RG58 coaxial cable transformer connection feeding all the loops to one 1:1 balun. Do you think it will work?
    thank you for your efforts

    OD5OJ, Bassam


    MOXON Antenna-Model.jpg
     
  2. K1VW

    K1VW Premium Subscriber QRZ Page

    I don’t have your answer but it’s a very interesting idea! I pondered it for a few seconds one time and then my train of thought went like this...

    The real question I think is can they all be on the same plane (like a yagi) or do you you have to separate them vertically, like a hexbeam to avoid having them interfere? I assume a hexbeam is like that for a reason.” At which point I thought “it’s probably more effort to build a stack of monoband Maxons, and that’s probably why you see hex beams for sale, and not multiband Maxon beams.” I’m not saying any of that is correct, just that’s what went thru my mind.
     
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I've built nested Moxons and have had good luck with 20m, 15 and 10m but have not had good luck trying to nest 17m with either a 20m or 15m antenna or 12m when there's already a 15m or 10m set of elements. There's a lot of interaction between the WARC band elements and the traditional band elements that tends to detune the adjacent elements.

    For the antennas I did build I just used RG-8x jumpers between the elements but it took some modeling and then experimentation to figure out the best coax lengths for those band to band jumpers. I haven't tried balanced feed line or coax jumper pairs for feeding the elements but with some planning and possible trimming in the field you can get at least the 20m, 15m, 10m elements to work pretty well when fed from the same coax and balun.

    Have you modeled this antenna, and if so what are you seeing in terms of both SWR curves, gain and F/B for the individual element sets vs the complete set of nested elements?

    You've probably already been over there, but there's some good information on multi-band feed systems for Moxons over at the Moxon Project: https://web.archive.org/web/20181124080519/http://www.moxonantennaproject.com/
     
    AJ5J likes this.
  4. OD5OJ

    OD5OJ Ham Member QRZ Page


    hello David, K7TRF

    thank you for your reply and valued feedback. i have not molded the design. there are many soft wares in the market but my experience in modeling is still limited. as i understand from you words, for 20,15,10m it can be done but to add the WARC bands it is difficult due to interaction with other wire bands. i shall try those 3 bands and see how it goes. i even designed a mix between yagi and moxon hope it will work. i used the same type of feed as optibeam. attached is a copy of my proposed design. it is made of aluminum obviously.
    tell me what you think.
    73s, OD5OJ
    OJ8-5.jpeg
     
  5. AJ5J

    AJ5J Ham Member QRZ Page

    Hello Bassam; I would have responded sooner but I was completely without internet here for 24 hours yesterday---our local wi-fi service was somehow disrupted.

    I was going to suggest The Moxon Antenna Project web site where I found my initial inspiration for building the four I have built so far (10m, 15m, 17m and a vertical one for 2m FM) but I see Dave already posted a link for it. Excellent source of info there. Somewhere in the MAP site there are some photos (or maybe a link) of a dual-band Moxon for 17m and 12m that a European ham built out of aluminum tubing if I recall correctly. It was very impressive and professionally done, in my opinion. I remember he said that interaction can be a problem with multiple Moxons---the more band the more interaction---so I built all of mine separately.

    Since you have limited space on your roof I would definitely try a 10-15-20 and another separate one for 12-17 more or less as K7TRF suggested above.

    I don't think being in the same plane is a problem but some vertical separation certainly can't hurt. Look at the Moxons with up-swept fiberglass spreaders and consider nesting the bands a la hexbeam style---that could be what you need to do for the best results (maybe even a five-band model would perform better thus configured). Wire and fiberglass would be lighter in weight, too.

    If you must use aluminum tube then I'd keep it simple and only do two or three bands for starters. Good luck with your experiments !

    73,

    Jeff (a fellow fan of Moxons, screwdrivers, small transmitting loops and other compact antenna wonders)
     
  6. AJ5J

    AJ5J Ham Member QRZ Page

    Agreed, I thought the same thing but I suspect that it boils down to being able to tune and re-tune carefully until a good match is obtained on all the bands. Difficult and tedious but not impossible; a lot like tuning a flat-plane cobweb.

    I will be curious as to Bassam's results; it could be quite useful to know for us Moxonites.

    73,

    Jeff
     
  7. OD5OJ

    OD5OJ Ham Member QRZ Page


    Dear Jeff

    it is always great to hear from you and learn from your previous experience.. after reading a lot of articles about multiband Moxon antenna I realize that it is hard to have a decent performing 5 band Moxon. a better option would be 10-15-20m one and another one for WARC bands 12-17m for obvious reasons related to radiation interaction between close bands.

    best regards and 73s
    OD5OJ
     
    AJ5J likes this.
  8. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    Just an FYI... I have a 20m yagi and a 17m yagi up in close proximity to one another on the top of my roof. I might remove the 17m yagi, because I'm pretty sure it's messing with my 20m yagi, and they're 7 to 8 meters away from each other. Not quite at the same height, but within a meter of the same height.
     
  9. AJ5J

    AJ5J Ham Member QRZ Page

    Hey Bassam; Here's a photo of that multi-band Moxon I was referring to the other day---just ran across it a moment ago accidentally. Wish I knew who the ham was that built it but I didn't tag it with his call. Maybe it will help a little, though!

    73, Jeff
    p_IMG_1004_1.jpg
     
  10. OD5OJ

    OD5OJ Ham Member QRZ Page


    thank you very much. really appreciated.
     
    AJ5J likes this.

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