Moxon with linear loaded tips?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K5WA, Mar 7, 2021.

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  1. K5WA

    K5WA Ham Member QRZ Page

    I'm sure this has been answered before but I have not been able to find the answer. I'm also sure my subject line is incorrect since this won't be a real Moxon antenna in this configuration and this may not be linear loading but it will catch people's attention who want to set me straight. ;-)

    I'm just asking if anybody has pulled their Moxon tips (dimension B and D in the standard drawing) back toward the boom to a riser above (or below) and in line with the element. My riser on each element is 3'. I barely know EZnec 6 but if I entered everything correctly, modelling actually shows slightly better gain (my main interest) than the standard Moxon when I use the 110' height I have available.

    Has anyone done this successfully? Did it work?

    Thanks and 73,

    Bob K5WA
     
  2. AK5B

    AK5B Ham Member QRZ Page

    Haven't ever tried this although I've built 4 different Moxons to date and am slowly working on a 5th. What you describe sounds very much like an antenna called a Double D that is in an RSGB book I got a dozen years ago, though. Even a tad smaller than a standard Moxon but with the same gain, supposedly.

    There's also been a Moxon thread in this forum that discusses adding "table legs" loading to the four corners in order to make the antenna smaller---but it probably reduces the gain in the process.

    I'll see if I can round up more info on the RSGB book and get back to you once I do.

    73,

    KEEP CALM
    AND
    MOXON ON


    Jeff
     
  3. SV2FNN

    SV2FNN Ham Member QRZ Page

    If you mean something like that ...(( the site = SM0DTK ))....It s O K....!!!!!!!!!!

    MH mini yagi for 18 MHz.

    This is a 2 element version of the MH antenna. As known the best gain obtains from a 2 element yagi counted per elements. Another element adds gain with 1-2 dB but makes the antenna bigger and heavier. F/B affects in small extent by more elements.
    This antenna is very small but the performance is like a full designed 2 el yagi with a reflector. Matching impedance is low but can be handled with a couple of quaterwave 50 ohms cables in parallell. Using a ATU you can feed the antenna directly with a 50 ohm coaxcable. As seen in the graph the best gain obtains in the lower part of the band and the best F/B in the higher portion of the band.

    [​IMG]
     
  4. K5WA

    K5WA Ham Member QRZ Page

    Thanks Jeff! Yes, I guess that Double-D and SV2FNN's referal are variations of what I'm trying to do with this 40M Moxonish antenna. The main reason I'm trying not to do a real Moxon is because this antenna will go about 2/3 the way up a tower so I'll need to either split an opening during installation and then reseal it or get this elevated tip idea to work. I like the sound of the "table legs" but I would need to make my legs of aluminum tubing rather than wire as I have it now. Wire drooping down would eventually wrap itself around the element in our Texas winds but a thin aluminum rod would work nicely, I'll bet. I'd be interested in knowing if anyone had modeled the "table leg" idea to see how much performance is lost.

    Bob K5WA
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Moxon, moxoff. Moxon, moxoff.

    Building arm strength, Daniel. You'll see.:)
     
    K2CAJ and N0TLD like this.
  6. AK5B

    AK5B Ham Member QRZ Page

    Roger that, Bob. See post #75 by K2CAJ in the thread "RW4HFN Antennas"---that's where I heard about the table legs idea. I'll find out about the Double D later tonight.

    73,

    Jeff
     
  7. AK5B

    AK5B Ham Member QRZ Page

    "Building Successful HF Antennas by Peter Dodd, G3LDO is the RSGB book I mentioned earlier; the Double D elements are folded back and upwards towards the center points to form sort of a pair of triangles and can be built with wire or tubing. Looks like a pyramid frame or one of RW4HFN's many geometric designs he often posts in this forum. :D

    Gain and F/B slightly less than a standard Moxon (5dbi free space and better than 20db F/B, so not bad for a compact version of an already small 2 el. beam).

    Total element length can be computed via the formula listed: 1417.83/f in MHz and the various element dimensions can also be computed with the other info in the book.

    Hope this helps, Bob!

    73,

    Jeff
     
  8. N4OGW

    N4OGW Ham Member QRZ Page

    Very little is lost with the "table legs" approach (within reason). I'm using hanging tails (short 1-2 feet) at the corners of my 40m wire moxon because they give an easy way to tune the elements.

    Folding things back in the plane of the antenna is much trickier to get to work.

    Tor N4OGW
     
    K2CAJ and AK5B like this.
  9. K5WA

    K5WA Ham Member QRZ Page

    Thanks Tor!

    I think I'll go with the table leg idea for dimension B and D of my Moxon-ish antenna.

    I appreciate everyone's suggestions. Hopefully, I'll get this thing up in the air in a month or two. Since it is at 110', I really don't need this antenna to be overly potent for me becayse even a dipole would be helpful. This would be my #3 40M antenna and will be fixed northeast for quick pops as needed. I'm basically rigless at the moment while waiting on a pair of K4 rigs to get made so I've got plenty of time on my hands to take care of low priority, but needed, maintenance and upkeep. I'll be glad when I get rigs back on the air in a contest again by late summer. ;-)
     
  10. AK5B

    AK5B Ham Member QRZ Page

    So Tor, did you build your Moxon a little shorter in the width dimension to start with or full-size and then added the legs and trimmed back the elements afterwards?

    Curious as how and when one actually implements them.

    73,

    Jeff
     

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