New antenna project...

Discussion in 'Amplitude Modulation' started by N2DTS, Jul 4, 2017.

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  1. N2DTS

    N2DTS Ham Member QRZ Page

    I did not find they interact much if you keep the ends away from the other legs.
    Mine is hosed up at the moment and somewhat tangled.

    In my case the 160, 80 and 40 meter legs are one antenna, the Alpha Delta LB.
    I had already removed a foot each end off the center to get all those bands into the phone portion.
    160 and 80 are very close, 40 is hosed up I think because 20 meters is touching it.
    20 meters low point is above 15 MHz but the icom tuner will tune it.
    15 is no where in sight, uses 40 meters....
    10 and 6 have low points but need trimming.

    Before I start thinking about adjusting it I have to stop the ends from touching.
    I think the end spacing from the other legs is what is critical.

    My 80 and 40 meter fan works great, the legs do not really seem to interact and the swr is low in the phone sections and its quite broad banded.
    I love being able to jump between 80 and 40 without having to tune or adjust anything, or even switch antenna's.
    One time it got tangled in a storm and the swr went nuts, but I lowered it and added a spreader each side and it has not happened again.
    Its been stable and trouble free for a few years now.
     
  2. N2DTS

    N2DTS Ham Member QRZ Page

    Made my first ever 6 meter contacts tonight.
    Very interesting band.
     
    N6YW likes this.
  3. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    I made some sketches of the antenna I am building and came up with an idea for keeping tension on the wires
    in order to maintain to maintain symmetry along the array using "Nico Sleeves" which are used with wire rope.
    These are pressed on using a Nico Press.
    Using these sleeves on both sides of the spreaders will maintain tension and prevent breakage of the spreaders.
    I'll see if this works as planned, Murphy being the final word!
    I may end up building this for the entire 80 meter band by employing the same technique as shown but using
    a long top element as the "long" element and the next 2 elements gradually going shorter.
    My thinking is that by physically making the antenna larger in circular mils so to speak, and adding shorter
    elements going towards 3900, or three wires that are self resonant throughout the band might be the ticket.
    The porcelain separators are old stock B&W banana plug frames as used for plug in coils which may prove to be
    too fragile and I may end up using PVC instead. What do you think?
    The idea of using the "Cage Dipole" approach is a lot of work and would be too heavy using the copper clad steel
    wire I have. I thought of using RG-8 coax as the elements instead but that introduces more problems physically
    than I am not willing to deal with. The Bazooka antenna has been considered too but they always fail and I doubt
    that antenna can handle the power I intend to be using.
    Look at the attached photos and post your comments, please.
    antenna1.jpg antenna2.jpg
     
    Last edited: Jul 19, 2017
  4. N2DTS

    N2DTS Ham Member QRZ Page

    I have found it best to just let the lower wires hang from the top one.
    On my 80/40 fan the 40 wires droop a bit between spreaders but that seems to be no bother at all.

    Only the top wire needs to be strong, the other legs can be thinner and lighter.
    A full size antenna is quite broad banded and its not an issue with tube finals to have a bit of swr.

    Weight is an issue, ceramic is heavy, plastic degrades quickly, so far, the fiberglass rods are holding up well.
    I have made open wire line a few times using plastic rack standoff's from work, using insulated wire and plastic (zip) wire ties.
    It worked well but fell apart quickly from the sunlight.

    On my 80/40 fan, I used about 8 inch separation, but read in a handbook people made fans out of twinlead with 1 inch spacing and it worked fine.
    So on my last antenna I used about 2.5 inch separation.

    I know a cage dipole has a very wide bandwidth, I have no idea what happens if you vary the lengths.
     
  5. N2DTS

    N2DTS Ham Member QRZ Page

    I did two adjustments, current low swr points;
    1,865
    3,823
    7,300
    13,540
    21,200
    28,200
    50.05

    20 meters is way off still, after taking a foot and a half off.
    Another foot should be close.
    40 and up are broad banded.
     
  6. N2DTS

    N2DTS Ham Member QRZ Page

    Did another adjustment on 20, unwound about 8 inches of foldback and cut it off, then folded back about 6 inches.
    Its now at 15.1 MHz.
    I will unfold the ends and hope to be very close.
    The legs do not seem to interact at all.
     
  7. KA4KOE

    KA4KOE Ham Member QRZ Page

    Bill, there are studies that show spreading the wires out in a fan to get the ends away from each other makes the system easier to tune. Google is your friend.
     
    N6YW likes this.
  8. N2DTS

    N2DTS Ham Member QRZ Page

    Did another adjustment on 20 and am now at 14.73, I should not have cut as much off last time...

    When I prune/adjust one band, I go and test the zero swr points on all the bands and I have not seen any change on the others (at all).
    This fan dipole is quite close together leg wise, about 2 inches.
    Current zero swr points:
    1,865
    3,823
    7,300
    14,730
    21,160
    28,200
    50,050
     
  9. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    After considering the posts and other information, I decided to make this antenna broad banded by using
    2-3 elements on both legs cut for low, middle and high points for the entire 80 meter band.
    With careful pruning I should be able to get the resonant points exactly on the frequencies I use the
    most. For 40-10, I can convert my other dipole for those bands. I am also considering a Delta Loop
    for 75 meters as an experiment. Lashing up a quicky is easy and because I use a "Halyard" on each pole
    with carabiner's, I can easily swap things out even though this would mean using the tuner.
    So many decisions but fun.
     
  10. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Here's a view of the wire spreaders I made from scrap military 3/8" HD Fiberglass sheet that I've
    had languishing around for a decade. I cut them into strips using a wet tile saw and diamond blade.
    I then drilled the wire holes, and screw holes on the sides which were then threaded to 6-32 in order
    to secure the wires in place. This will keep them taught without resorting to wire wrap or Nico
    press sleeves, which are aluminum, so nix that idea altogether.
    Stainless Steel screws do the trick!
    Judges? IMG_5518.JPG
     

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