My Homebrew, Fan Dipole (pics)

Discussion in 'Amateur Radio Equipment Reviews' started by KY4SPS, Apr 18, 2008.

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  1. KY4SPS

    KY4SPS Ham Member QRZ Page

    This is my homebrew, fan dipole. It was made for me by a local ham (N8KYX). Performs really well from 80 - 10. Only modification I did, was add an MFJ 1:1 Balun. Took some pics tonight at twilight.

    [​IMG]

    [​IMG]
     
    Last edited: Apr 18, 2008
  2. W6IRE

    W6IRE Guest

    That's a sweet antenna. How has it been performing? I'm thinking of home brewing the same thing. Are you using a tuner? What is holding up the ends of the antenna, masts?Come on man, don't hold back!
     
  3. CT2JUT

    CT2JUT Ham Member QRZ Page

    Nice work mate!

    Looks like mine! :)

    Though mine is slighlty inverted-v due to roof space, and has a 10m hard-aluminium mast in the middle where the RG213 coaxial runs inside.

    It has three 1/2 wave elements (40m, 17m and 12m bands), but i´m able to work all bands, but 80m band with poor performance.

    I don´t use a balun, i just use the ATU, but i´m considering to take a chance on the 1:1 balun.

    I don´t know how high is yours, but i believe it´s a very good performer!

    For bands lower than 40m, a good grounding is a must! Do not mix with the house´s grounding, otherwise you´ll get plenty of noise.

    It´s so much fun to run your homemade antennas, isn´t it? :)

    QSO´s done this month from Lisbon, Portugal at my QRP station running 130W:

    40m : Australia 58, Brazil 59+, Greenland 58, Kazahkistan 58

    17m : Japan 53, Several Central/South America´s 57, Tazahkistan 57

    12m : Brazil 55, Niger 57


    And many many others!

    This information is only to encourage some other fans/newbies, for this type of antenna, that performs reasonable for it´s cost, and not for self-esteam, as the reports are not amazing, neither is a direccional antenna.

    Of course it´s difficult to break pile-ups, but now and then i can do them at 2nd or 3rd call! I wonder why...


    73´s from Portugal!

    Miguel
     
    Last edited: Apr 22, 2008
  4. KY4SPS

    KY4SPS Ham Member QRZ Page

    Thanks for the props! The antenna was made for me about 7 months before purchasing my first HF rig. It is strung up in trees on both ends and held up by weed eater string. I tried 60lb test line in the beginning, but it broke!

    I do use a tuner, but bypassed it once and it still had a great SWR. The worse tune is on 40M with about a 1.3:1. Using a tuner, I can very easily tune a flat SWR on all other bands.

    It performs really well and I run 100 watts max (Yaesu 897D). I have made contacts to Portugal, France, Costa Rica, Brazil, Caribbean, Cuba, Central Mexico, Hawaii and all over the USA. I have RX'd Australia, but have yet to make contact. I have no doubt that it will though.

    Email N8KYX for info on constucting this antenna, I'm sure he'll be happy to share his knowledge.
     
  5. AI4IJ

    AI4IJ Ham Member QRZ Page


    That is a very nice antenna! I just built a five band fan dipole to cover 40M, 20M, 17M, 15M, and 10M. 40M and 15M use the same wire (it's 3/2 waves on 15M). I opted not to include 75M/80M in this particular antenna; because, the resonant length changes so much across the band that I would need a tuner, anyway. And, my goal was to build an antenna that did not require a tuner.

    A fan dipole, like any other antenna, is a compromise antenna. In this case, the biggest compromise, in my opinion, is in operational bandwidth, as compared to a single monoband dipole. I know this seems counterintuitive; but, on each individual band, the 1.5:1 SWR bandwidth is significantly reduced, as compared with a monoband dipole for the same band.

    So, I had to make a couple of choices in my design and tuning:

    First of all, the narrower the spacing between the elements, the more narrow will be the bandwidth of coverage on each band. So, to address this, I had to decide between a wider bandwidth and more difficult implementation (tapering the elements apart, while supporting them adequately) and a lower profile antenna that was easier to transport, raise, and lower, but that has a narrower operating bandwidth.

    I chose a one inch spacing between the elements. This allows for a compact antenna that can be easily rolled up and stuffed into a nylon bag and carried with me on camping and day trips where I will be operating portable. But, the trade-off in bandwidth meant that I had to choose which end of each band I wanted to operate. Since, I do not currently use CW, I chose to tune the elements for the phone portions of each band - where possible.

    On 40M, I chose to tune the elements for the CW end of the band, at about 7100kHz. Why? Because, I wanted resonance on 15M to fall within the phone portion of the band; and, if I tuned 40M for the phone portion of that band, the elements would not even be resonant within the 15M band - for example, if I resonate the antenna at 7200kHz, resonance on 15M would be found at 21.600MHz. But, by choosing to resonate the 40M elements at 7100kHz, resonance on 15M is at 21.300MHz.

    75M/80M is a wide enough band, in terms of variation in wavelength, that it justifies a fan dipole that is made up of elements that ALL fall within the 75M/80M band - perhaps, one element for 3.5MHz, one element for 3.7MHz, and one element for 3.9MHz. This would give functionality on 75M/80M without the use of a tuner.

    I tried to take a picture of my five band fan dipole installed at 50ft. hanging from a tree limb, with the elements in an inverted V configuration and an included angle of about 90 degrees; but, the antenna is virtually invisible in the picture, with the tree branches and leaves in the background. But, I've included a couple of pics of the feedpoint/insulator at the bottom. And, I've written up instructions for building one that you can read here:

    To build this antenna, I used the following:

    2 - 10 ft. sticks of 1/2" schedule 40 PVC pipe (to be cut up into pieces to be used as spacers for the elements

    1 - 1/4" thick plastic cutting board from Walmart (plain white - to be used as the feedpoint and center insulator

    1 - Mirror mount bracket for a standard 3/8" whip style antenna with SO-239 connector and feedthru insulator

    1 - Roll of electrical tape

    11 - 1/4" ring connectors

    1 - 3/8" ring connector

    8 - 1/4" x 1.5" stainless steel hex bolts

    16 - 1/4" flat washers

    8 - 1/4" lock washers

    8 - 1/4" nuts

    146ft. - 14 gauge insulated wire to accomodate the elements.

    1 - Can spray paint - your choice of color (optional)

    Begin by measuring and cutting the wire for the elements as follows:

    2 - 34ft. for 40M/15M (1/2 wave on 40M, 3/2 wave on 15M)

    2 - 17ft. for 20M

    2 - 13ft. 4" for 17M

    2 - 8ft. 6" for 10M

    This gives you four elements on either side of the feedpoint - 1 for each band x 2 (15M uses the 40M elements).

    Next, cut the PVC spacers as follows:

    16 - 5" pieces
    10 - 4" pieces
    6 - 3" pieces

    Use a 1/8" drill bit to drill holes spaced 1" apart in each of the spacers as follows:

    Drill four holes in the 5" pieces

    Drill three holes in the 4" pieces

    Drill two holes in the 3" pieces

    It is important that the holes you drill be just large enough to accomodate the wire, and no larger. So, if you use wire other than 14 gauge insulated, you may need to choose a different drill bit. Just leave one inch at each end of the spacer and space the holes one inch apart. It is also important that your holes be straight through the center of the PVC pipe and consistently spaced - you will be passing the wires through both holes.

    Next, I chose to paint the spacers with a flat black paint ($0.99 per can at Walmart - one can needed). First of all, because it is more aesthetically pleasing, and secondly, to provide additional UV protection from the Sun. But, this is entirely optional.

    Next, crimp and solder 1/4" ring connectors to one end of each of the dipole elements.

    Next, cut a center feedpoint/insulator out of the cutting board. I cut mine 6" x 5", with the 6" dimension vertical.

    Remove the rear plate of the mirror mount and use only the angle aluminum bracket and the feed-thru connector.

    Align the angle aluminum bracket with the SO-239 feed-thru with the bottom center of the center feedpoint/insulator and mark where the holes should be. Then, use the same bracket as a template for four more holes above those - to be used as attachment points for the elements. Then, drill all of those 1/4" holes.

    Next, drill a 3/8" hole in the middle of the top of the center feedpoint/insulator to be used as a mounting point for rope or string for supporting the antenna.

    Then, drill four 3/8" holes down each side of the center feedpoint/insulator spaced 1" apart to be used for stress relief loops in the wire elements.

    Then, assemble the antenna as follows:

    Lay the center feedpoint/insulator in the floor and attach all of elements to ONE SIDE of the antenna, with the 40M/15M element on the top, then followed by the 20M element, then the 17M element, then the 10M element on the bottom. Put one loop in each element as stress relief and loosely attached it to one of the two bolts on this side of the center feedpoint/insulator (there will be two elements attached to each of the four holes you drilled above the aluminum feedpoint bracket). I attached the 40M/15M element and the 20M elements together and the 17M and 10M elements together, then tied both of those two points together with a short piece of copper wire on each side.

    Use a short piece of wire to connect one side of the antenna to the metal bracket and another short piece of wire to attach the 3/8" stud hole in the feed-thru to the other side of the antenna. After making all connections, tighten them all.

    Then, thread the PVC spacers onto the wire elements. Starting with the longest and working to the shortest, thread the spacers onto the elements, leaving about one foot of space between each one. Try to adjust the spacing of the spacers at the ends of the elements to ensure that there is at least six inches extra wire hanging out of the element on the last spacer.

    Then, starting at the center and only on the 40M/15M element, pull the element taught and wrap a few rounds of electrical tape on either side of the PVC spacer to secure the spacer in place. Work your way all the way down the length of the 40M/15M element before securing the other elements to the spacers. Then, move to the next higher frequency band. all the way down the length of the element, and repeat, until you're done. The electrical tape is an easy, inexpensive, and effective means of immobilizing the spacers; but, this is, perhaps, one of the most time consuming parts of building one of these antennas. So, if you can contrive a better way to do this, let me know about it.

    After you've completed one side, you can roll it up, first by rolling up the excess 16+ feet, or so, of the 40M/15M element and securing it with a wire tie, and then, by simply rolling up the rest of the elements in about a one foot diameter roll. Then, repeat the process with the other side of the antenna. I did it this way to fit the antenna into a room in the basement. If you're assembling the antenna in a larger room or outside, you can leave the antenna stretched out, if you like.

    Next, find a suitable mounting point that will support the entire weight of the antenna and ensure that you can easily raise and lower the antenna during the tuning process.

    Tune the antenna by raising it and supporting the ends of the antenna as they will be in the final installation. Check the SWR on the 40M band and adjust the elements for resonance at the LOW end of the band. Why? Because, you will also be using this element for 15M; and, three times the low end of the 40M band places resonance on 15M in the phone portion of that band. If you adjust 40M for the phone portion, your SWR will be high on 15M. I found that I had NO trimming needed on 40M - but, I installed the antenna as an inverted V with about 90 degrees between the elements. This meant that 15M needed no adjustment, either.

    Raise and lower the antenna as necessary, making your SWR measurements in the final installation configuration, and NOT near the ground.

    After getting 40M/15M tuned, move to 20M, then 17M, then finally 10M. Take no more than 1/2 inch off at a time, until you achieve resonance where you want it. An SWR analyzer will make short work of the tuning process.

    73
    Richard
    AI4IJ
     
  6. KY4SPS

    KY4SPS Ham Member QRZ Page

    I can now add Chile, and Australia to my list. 20 meters opened up nicely Friday evening. 2nd contact to Hawaii as well.:cool:
     
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