1. You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
    Dismiss Notice

Is the match on my DIY Moxon OK?

Discussion in 'CB Antennas' started by Alan Blackmon, Oct 15, 2018.

  1. Alan Blackmon

    Alan Blackmon Member

    Joined:
    Apr 11, 2017
    Messages:
    20
    Likes Received:
    11
    Recently I was able to acquire a MFJ antenna analyzer. I love it. I used it to check my various antenna systems. During a discussion with a local CB shop operator who is also a licensed ham I was informed that my Moxon may have a problem. He was concerned about my high X factor reading. He warned me I could be doing some damage on the finals in my CB. I personally have no idea what the X factor is or what it is telling me. This is a new area for me.

    Well having built the Moxon this last summer I only had a SWR meter to work with and now I have a device that gives me more information than my SWR meter. I have done a search on this but the search results have not been helpful So I turn to the group here. Is the results for my X factor a problem for me or not. I have attached some pictures of my analyzer results and a shot of the balun I also installed at the feed point of the antenna. The shots of the analyzer are lower CB and channels and upper CB channels or there about. As you see the X factor is higher on the upper frequency. As I rotate the antenna (armstrong) the X factor does change. It gets worse and better as it changes compass heading. Highest reading is 19 for X factor. Generally it is worse as it points towards the roof structure of my house. That is also the direction of my vertical antenna. In the first photo the antenna is pointing SW by S. Any other comps heading and the results are higher for X factor. SWR does alter a bit but nothing alarming. The Moxon is 15 feet over the top of a metal awning on the back of my house. It is mounted on the corner of the awning. The awning is 9 feet high and the mast is 14 above that. I am 23 feet high to the feed point. These readings were taken at the bottom of the mast or 14 feet from the feed point. The Balun pictured is at the feed point. Anyway I'm told I should not use the antenna with these results. What say you here? Thanks for your help guys. IMG_2225.jpg IMG_2226.jpg IMG_2228.jpg


     

  2. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

    Joined:
    Apr 23, 2018
    Messages:
    1,382
    Likes Received:
    1,028
    MFJSWR.jpg
     
    midnight special likes this.
  3. Alan Blackmon

    Alan Blackmon Member

    Joined:
    Apr 11, 2017
    Messages:
    20
    Likes Received:
    11
    Thanks Handy Andy. I would agree I am good with those kind of numbers for SWR. According to the guy who tells me my X factors are to high (which I know nothing about) there is still some reflection getting back to my finals. I have no idea what he is talking about because I have no idea what this measurement of X factor (X=4 and X=12 in the photos) has to do with anything and this guy says it did take out my finals on my Bearcat 980.

    Now I personally think my own monkeying around with my Bearcat took out my finals. I believe I set the output to high and the finals overheated due to my own negligence not some X factor measurement. I am just wondering what is this measurement anyway and why is this guy so upset about it? I'm here to find out if it really is a concern or someones whatever that I really need not take heed to? Google is just not helpful with my finding an answer. There may of course be the answer of IT DON'T MATTER despite what this guy said. I'm just less knowledgeable than he is and am seeking the truth of it all.
     
  4. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

    Joined:
    Apr 23, 2018
    Messages:
    1,382
    Likes Received:
    1,028
    The meter has a redundant system - one - the digital LCD display in the mode you set it up in to do your measurements - showed 1.1 with "SWR" just below it - that is the digital display and what it thinks you are at. That is the reflected too, that is calibrated by the meter you just turn it on.

    SWR the needle meter on your left - is actual SWR reflect per power on. Verified by digital display - the two may vary slightly - don't be too concerned. At the current deflection you see in your photos you have nothing to worry about - but it is letting you know of interactions also with nearby objects in the "Near field" and are attempting to couple with it (interact)

    As you already discovered - the Left Knob adjusts your "built in frequency sweep" to determine the "null point" or lowest SWR - and what looks like comparing both photos - the SWR is LOWER on the LONGER wavelength. Which can explain the "why" R=45 and R=53 with your X = (reactive parts) starting to climb at the shorter wavelength frequency (Channel 40) - may indicate you need capacitance - to offset inductance - or just shorten the driven element by about 1/4" - you're that darn close - so don't kill yourself over less than one inch difference and with close coupling of objects nearby - it makes this even harder to truly see any difference once it's been set 1:1 flat over most of your band of interest.

    Enjoy that little tool, heres' a PDF of it (B) if you need - it can't really offer much for there are VOLUMES of information about the tool elsewhere on the net that describe it better - about what to do with this and that. For it can do a lot but DOES NOT fix toast and flush your commode in the morning - not that you want it too...
     

    Attached Files:

    Shadetree Mechanic likes this.
  5. Alan Blackmon

    Alan Blackmon Member

    Joined:
    Apr 11, 2017
    Messages:
    20
    Likes Received:
    11
    Thanks so much. I do think all is well with the antenna. You have explained better than what the other guy ever was able to. Well actually he never offered an explanation. I can see where the antenna is trying its darnedest to couple with the surroundings. As it points to the house it does slightly go up in SWR but only slightly. It is still in a safe operable range.

    Thanks so much for your help. I am pretty sure my radio was not killed by the antenna but my own screwdriver putting the output just a bit over what I should have done. That won't be happening again.
     
    binrat and Handy Andy like this.
  6. M0GVZ

    M0GVZ Sr. Member

    Joined:
    Oct 18, 2011
    Messages:
    1,380
    Likes Received:
    735
    It wasn't killed by the antenna. If a high value of X kills a radio even if the SWR is low then mine should've died years ago as I use a screwdriver antenna with my Kenwood TS480 and the value of X is well into double digits on some bands.
     

Share This Page

  • About Us

    The WorldwideDX Radio Forum was originally established in 2001. We pride ourselves on welcoming Radio Hobby enthusiasts of all types, while offering unbiased, informative, and friendly discussion among the members. We are working every day to make sure our community is the best Radio Hobbyist's site.
  • Like us on Facebook

  • Premium VIP Member

    The management works very hard to make sure the community is running the best software, best designs, and all the other bells and whistles. Care to buy us a beer? We'd really appreciate it!

    Donate to us!