Minimum height for a full wave loop

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KJ6AJL, May 2, 2012.

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  1. KJ6AJL

    KJ6AJL Ham Member QRZ Page

    I'm thinking about taking on the challenge of putting up a full wave loop for 160M and I'm curious what the minimum height should be. Is it worth the time and money to put one up if I can only get it 20-30 feet off the ground? I know I won't work much DX on 160 at that height, but it will be feed with ladder line, so I will be using it on other bands as well. Also, this loop would encircle my other antennas and I need to know how they will interact. How far away from the loop do they need to be? I'd like to be able to share supports to keep the cost down.

  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    That's so low the wire sag will make it a lot lower in between supports...may not be worth the effort.

    However where there's a will...

    I work Don KG9OM quite often. He uses loops about 50' above ground as shown here:

    ...and they work well for him. But those are at 50' above ground. I know Don experimented a lot with this, back at his old QTH in KY and also at his current one. His discussion on the website link provided above provides some insight about what he found.
  3. W5DXP

    W5DXP Ham Member QRZ Page

    A full-wave loop radiates broadside to the loop. If the loop is horizontal, most of the radiation will be almost straight up. At any reasonable height on 160m, that makes it an NVIS antenna. Or are you talking about a vertical loop?
  4. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Worthwhile? Compared to what? :)
    What are your objectives? If you are happy working regionally this would be good. If you want to work Europe from California, then you need it a lot higher.

    Nobody can accurately answer all your questions. Put the antenna up. Do what you can. You won't learn anything if you don't try it!
  5. N0AZZ

    N0AZZ Ham Member QRZ Page

    I will tell you how mine worked it had varying heights using existing supports @ 50/40/25/18' and a very ragged rectangle. Ladder Line is a PITA to use and not necessary at all. I used coax all the way and it was fed from a corner at my tower close to the house to a tuner it worked from 6-160m. It was the best antenna that I have used and I have a lot of antennas for North and Central America on the low bands 30-160m. In fact in the first 160m SSB Contest I worked 43 states and 19 enties under poor conditions it was excellent on 80/160m.

    I had yagis and beams for all bands 432-40m and verticals for 440-160m as well and dipoles covering the same so I did a few to compare to. It is known as a quiet antenna the jury is out here on that, granted it's not a great DX antenna but did work a little a few times mostly EU's. If you want a good low band antenna for NA,CA it's well worth putting up and 30' will surprise you I think all you need is wire and a balun, coax.
  6. KJ6AJL

    KJ6AJL Ham Member QRZ Page

    Thanks for the info, I'll check out that web site. My goal is to experiment and have fun. I'd like to have something that can work DX on 80M though. My understanding was that a loop cut for 160 would beam the majority of the energy straight up, but on 80M it would radiate at a much lower angle. Is that accurate?
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Not at 20-30 feet, it won't. Still, even if it has substantially less than 0 dBd gain at lower angles, you'll make contacts!

    I've worked VKs on 80m from my van using a 7' tall mobile whip; it's all in "timing" and being there.

    As Don Wallace W6AM told me 35 years ago when I asked him his secret for working so much DX: "Be there when the DX is."
  8. AD5ZC

    AD5ZC Ham Member QRZ Page

    Horizontal loops don't start radiating off the sides until you get to about 1.5 wavelength. Most don't use 1.5 wavelength loops because the impedances are atrocious every odd half wavelength. So really, 2 wavelengths is where you want to be if your looking for radiation in the direction and angle that you would need to work DX. If you have the room for a 2 wavelength 160 meter horizontal loop then go for it. I had an 80 meter loop that was gangbusters on the higher bands where it was more than 2 wavelengths long even though on one side of the loop it did indeed droop quite a bit and was probably lower than 20 feet. It also worked VERY well locally on 80.
  9. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Antenna height is sometimes a variable that can be difficult. Most antenna modeling programs will allow you to put in the soil charateristics. This can have a deep impact on how well it will work. At 30 feet with normal soil it would be a cloud warmer but if you had really bad soil the effective height appears much higher and the antenna will perform in a very different way. Different can be better. If you can model your idea you would see what performance you should get. Modeling for just one antenna might be a bit much but with it you can find the exact point where you should be for the perfomance you want.
    The idea of put it up and try it is a good one too. That's how it was done even a few years ago. It can be an interesting experiment. I have an antenna that has it's bottom section 6 feet of the ground and the top is 16 feet up. I have worked all over the world with it on 40 meters. It works on 60 meters and 75/80 meters as well. The modeling for this antenna shows the best performance would be if I could get the bottom up 10 more feet.
    So try it you might be pleasantly surprised.
  10. N5QM

    N5QM Ham Member QRZ Page

    Just for clarity and my education, what might be considered bad soil? In my area, the topsoil is maybe 2 - 3 inches deep and then it is mostly rock and shale. I would expect this to fall under the "bad" category which seems would be good for a dipole and bad for a vertical with radials, is my understanding correct?

  11. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I'd say that's pretty far off.

    Soil conductivity is important for horizontally polarized antennas, and the higher it is (closest to sea water, or better still, a metallic screen), the more gain compared with a dipole in free space. The angle at which that gain is achieved varies with antenna height above earth, but on HF you're never so high as to not benefit from that gain, and the highest possible soil conductivity is best.
  12. K8JD

    K8JD Ham Member QRZ Page

    FW loop

    For the best high angle signal the full wave loop should be 1/4 wave above ground. My 40M loop is a very effective short hop antenna at 35 ft..
    So a 160M FW loop would have to be up 120 ft for max effieiency.
    It seems odd to use a horiz loop that's a full wave on one band on higher frequencies. Why not just change the angles and use it as a multiwave rhombic on those higher frequencies.
  13. N5QM

    N5QM Ham Member QRZ Page

    Ok, than under what conditions can poor soil be better?

  14. VE3FMC

    VE3FMC XML Subscriber QRZ Page

    When I upgraded to HF privileges in 1994 I put up a full wave horizontal loop for 80 M, coax fed. Feed point was right above my shack at 29 feet. Then the loop sloped down to about 15 feet at one corner, 15 feet at another corner. Came up to about 20 feet to a support on the other end of the house. Over to some trees, so it was only about 10-12 feet off the ground there. Then back to the tower at the feed point.

    I managed to get WAS with 100 watts on 75 M phone with that antenna. Also worked some DX. Mind you my signal wasn't strong to the DX stations but I managed to work them. However I had a killer signal within a 300 mile radius. One guy in Ohio near Dayton always thought I was running big power here because I was always 30-40 over when I talked to him.

    Not sure what your results would be like on 160 but I had fun with that low loop I had up. Didn't know how crappy or how well it worked because I had nothing to compare it too :D
  15. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Having played with 4NEC2 a lot plugging in different soil resistivities I couldn't see any condition under which poor soil would be better.
  16. W5DXP

    W5DXP Ham Member QRZ Page

    I've heard that laying an antenna on the sand in the middle of the Sahara Desert is almost like free space.:)
  17. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    It may be, but I wouldn't want "free space," that gives up too much useful gain where it's needed.:eek:
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