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30 meter Delta Loop - how high??

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W4PG, Dec 18, 2012.

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  1. W4PG

    W4PG Super Moderator Volunteer Moderator Platinum Subscriber QRZ Page

    I currently lack any decent antenna for 30 meters and was thinking of putting up a delta loop. I can easily hang it from my tower. My plan was to have the apex at the top and to feed the loop from one of the sides at the bottom in order to get vertical polarization. My primary use will be DX.

    Using the formula 1005/(freq in Mhz) the total length comes to about 99.26 feet using 10.125 as the center frequency. Therefore each side will be about 33 feet. If I can remember my trigonometry right, the height if the delta was a perfect triangle would be about 28.6 feet from the apex to the bottom horizontal wire. OK, no problem.

    I don't plan to use the delta on any band other than 30, so I was also planning to make a 1/4 wave matching section of 75 ohm coax then run the distance to the shack with 50 ohm coax.

    My question is, how high should I position this beast? I've read different things and wonder if anyone has any experience with a similar antenna?? The top of my tower is 89 feet, but I was thinking of hanging it from about 45 to 50 feet or so, so the bottom horizontal leg would be 20 something feet off the ground depending.

    From what I've read, when vertically polarized the antenna acts somewhat like two verticals in phase. If this is true, then maybe I don't want to place the antenna too high as that might disrupt the pattern?? My goal is to maintain a low angle of radiation for DX purposes.

    Any ideas of the best height above ground for the lower horizontal portion??
  2. KU3X

    KU3X Ham Member QRZ Page

    The base of my full size 80 meter delta loop is only 8 feet above ground. With that antenna I have worked VK's long path from Easter PA and I am 100 feet below average terrain. If you look at the 8 feet on 80 meters and convert to wavelenths for that band, it's not very high. Now scale that down to the 30 meter band and it's like putting your antenna about 3 feet above the ground. Now I am not suggesting you mount your antenna that low but I would mount it high enough to clear any buildings that are around your antenna. The base of my 30 meter delta loop is about 22 feet above the ground and I am happy with its performance.

    Since you have an 89 foot tower, consider a full size delta loop for 80 meters and nest the 30 meter loop inside of it.

    Barry, KU3X
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Actually if you cut the 80m delta loop for the low end (3.50 MHz) it should resonate again at 10.5 MHz, just above the 30m band and work pretty well there.:eek:
  4. KU3X

    KU3X Ham Member QRZ Page

    That may be true, but you will have a much higher angle of radiation on 30 meters and this would not be a good antenna for working DX.
    That's not to say working DX with this arrangement is impossible, but not the best way to go.
  5. KO6WB

    KO6WB Premium Subscriber QRZ Page

    To feed the loop at the lower corner isn't quite vertical. It's pretty darn close though. For accurate vertical polarization you would need to go 0.08 wave up from the corner which is just a little less than 8 inches. Go figure?
    The height of the loop can be much lower and it'll still give a low angle takeoff good for DX. Higher up is not a bad thing. Make sure to space the loop far enough away from the tower. The tower is vertical as would be your polarization. So keep that spacing in mind. The coupling should be minimized.
    Hope this helps
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    For a more interesting project, and one that will keep you busy, switch the tower to one made of wood. Most of the interaction problems will disappear.

    Oh, and take out fire insurance on it (and maybe termite insurance).
  7. VK4FUQ

    VK4FUQ Ham Member QRZ Page

    G'day all, yes I concur. Try and keep all metal (mast etc) outside of the loop enclosed area. I learned this lesson the hard way! Regards, Felix vk4fuq.
  8. K8JD

    K8JD Ham Member QRZ Page

    I had a delta loop for 30 M up for awhile and it was flat, all about 30 ft above ground, hung over tree branches, (just over a quarter wave high).
    I fed it at one corner with a 75 ohm Q section then RG8x into the house.
    It was designed to compliment the low angle Butternut Vertical I had with a high angle launch for eastern North America. I had a much stronger signal, with the loop, in the target area, than the vertical could give me. I was uning a MFJ9030 at the time, my main rig (TS520) had no WARC bands.
    I worked a lot of western states and Europe with the vertical with 5 Watts.
    If you want abetter DX ant than a vertical, on 30M, get the loop up so the lowest part is 1/2 wave above ground !. This is why nobody uses cubical quads below 14 MHz !
    Last edited: Dec 20, 2012
  9. W4PG

    W4PG Super Moderator Volunteer Moderator Platinum Subscriber QRZ Page

    Got the Delta Loop up today. Hardest part was attaching a 4 foot piece of aluminum to the tower for a pully! Horizontal bottom section is about 25 feet off the ground and the top apex somewhere about 50 I guess. Fed it with a 16 foot piece of 75 ohm RG-11 coax then 50 ohm to the shack. Feed point is about 8 inches up from one side so it's vertically polarized for DX. SWR about 1.2 to 1 right out'a the gate and less than 1.5 across the whole band.

    First contact was A61BK so it must work! Will have a go and see how it does! So far so good! :)
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