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Magnetic Loop

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AC2FO, Oct 14, 2012.

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  1. AC2FO

    AC2FO Premium Subscriber QRZ Page

    Last week a friend of mine AC2IQ and I were talking about antennas , and the magnetic loop antenna came up I mentioned how small they are and how you can tune several bands with it, So he said let's build one. Well about a hour later he had one all finished up with remote tuning cap and all. we lowered his tower down and put it on top, oriented horizontal, it worked great 10-20 meters. Well of course now the wheels start turning, we now need one for th Top Bands. So a quick run to Lowes to buy some parts $500.00 and 2 days later this antenna was born, remote from the shack fully adjustable variable capacitor and all . It took some doing to get it in the air. These pics are also on his qrz site in case you want to see them there AC2IQ

    [​IMG]



    [​IMG]

    [​IMG]
     
    Last edited: Oct 14, 2012
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    How's it work?
     
  3. AC2FO

    AC2FO Premium Subscriber QRZ Page

    It was smoking when I left.
     
  4. K4SAV

    K4SAV Ham Member QRZ Page

    What is the wind area of that monster?
     
  5. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Does it whistle?
     
  6. AC2FO

    AC2FO Premium Subscriber QRZ Page

    Good Question It was a beast getting it up the first time, just let me say that. I have a video will have to upload later.
     
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    160m is a strange band which takes some knowledge.

    "Anybody" can make domesic contacts. Try working VKs and let us know how that worked out.
     
  8. AC2FO

    AC2FO Premium Subscriber QRZ Page


    Maybe I missed it did anyone say anything about making any contacts domestic or otherwise? It's a experiment with a magnetic loop well see how it works out, but AC2IQ used to be a broadcast engineer I think he will be ok on 160.
     
  9. VE3ES

    VE3ES Ham Member QRZ Page

    There is always somebody with a negative comment.
     
  10. WX7G

    WX7G Ham Member QRZ Page

    Wow that is a nice antenna and an article in QST is in order! It will work even better if oriented vertically.

    The ARRL 160 meter contest is in early December and that would be a great time give the antenna a test.
     
    Last edited: Oct 14, 2012
  11. G4LNA

    G4LNA Ham Member QRZ Page

    Interesting, normally they are orientated vertically, so it will be interesting to see how it works, it's a bit of a beast looking at it. It reminds me of the old Capital Radio on the old pirate ship King David that tried a loop antenna without much success.
     
  12. AC2FO

    AC2FO Premium Subscriber QRZ Page

    If it don't work well we can always use it as a swimming pool so all is not lost.
     
    Last edited: Oct 14, 2012
  13. AC2FO

    AC2FO Premium Subscriber QRZ Page

    Last week, he had the 3' diameter loop on top of tower at about 80' and it was oriented horizontally and suprisingly it seemed to work very well with contacts into indonesia thats what brought on this one.
     
    Last edited: Oct 14, 2012
  14. KL7AJ

    KL7AJ Ham Member QRZ Page

    It would be interesting to model the coupling between the loop and the tower itself. I suspect your tower's doing a bit of radiating too! If such is the case, your net result could be largely CIRCULARLY polarized, which has some interesting advantages on 160. See my recent QST article, "Three wrong assumptions about the ionosphere."

    Anyway....it's so refreshing to see something so bold, audacious, and out of the box. Please collect and record some objective performance data.

    Eric
     
  15. AD5ZC

    AD5ZC Ham Member QRZ Page

    If nothing else, it looks really really cool. :)
     
  16. NH7RO

    NH7RO Ham Member QRZ Page

    +1 on the above although I must admit I thought it was some sort of photoshopped hoax---wow, that giant loop is impressive and I'm glad to know that it's for real!

    73, Jeff
     
  17. AC2FO

    AC2FO Premium Subscriber QRZ Page

    LOL, Yes it is for real, if you look you can see the capacitor .

    [​IMG]
     
    Last edited: Oct 14, 2012
  18. KO6WB

    KO6WB Premium Subscriber QRZ Page

    The proximity of the tower through the middle is a cause for concern as is the horizontal orientation If you have ever tried to get something that big in a vertical position and at least one loop diameter above ground then you have no idea what a difficult task that is.
    I use a magnetic loop daily on 40 meters and it'll tune down to 80/75 with no problem. In my operations on 40 meters DX is easily done. This depends on conditions but for those that have ever tried DX on 40 meters it can be an adventure at times. My loop is made of 1" copper pipe and is 40 feet in circumference. Mounted off the ground 11 feet up. Played around with a modeling program last night and found what everybody else has found. A greater conductor diameter will give you much better performance but at the same time the loop diameter becomes smaller. If you could make a loop 22.6 inches in conductor diameter and have a total length of 20.634 feet with a loop diameter of 6.571 feet then you'll have a loop that can tune MF/HF all bands. The Q on 160 meters will be over 5000 with a 3db bandwidth of just over 300Hz. The efficiency is just over 25% on 160 meters (not bad), 77% on 80 meters, 93% on 60 meters, 97% on 40 meters, 99% on 30 meters, 99% on 20 meters, 99.9% on 17 meters (the bandwidth has increased to 800KHz), 99.9% on 15 meters, and on 10 meters you still have the 99.9% efficiency with a ending bandwidth of 4.5MHz. This is if everything is perfect, and it won't be but it is interesting. If you add 1 milliohm of additional resistance then the efficiency drops from 25% on 160 meters to 15.5% and the Q goes from almost the 6000 mark down to just over the 3500 mark. Naturally if Q drops then bandwidth widens and it would now be 500Hz. This is just 1 milliohm. The loop I currently run has an added resistance of 3.5 milliohms which at 40 meters reduces the efficiency from 93% to 92.9%. Not worth worrying about and the effect of the added resistance at 80 meters drops the efficiency from 54.6% to 53.3%. Again, not worth worrying about.
    My magnetic loop is vertical and they work better in that position. Magnetic loops that are vertical do not do as well when raised up to 1/2 wave above ground. Horizontal loops need to be up 1/2 wave to work properly.
    I am intrigued by this construction. It took me days to get my 10 foot square loop up and operating (I'm getting old) and to have the ability to put one that large together is amazing in it's own regard.
    I would be interested in performance reports. Compare the antenna to another possibly a nearby fellow amateur running a dipole, an L, Vee , full wave loop and vertical and see how this antenna works at various distances.
    Let us know what you've found
    73
    Gary
     
  19. WH2HAO

    WH2HAO QRZ Moderator QRZ Page

    I think you are on to something. You gave me an idea, what about taking a large galvanized swimming pool and cutting the bottom out ?? !! I like it, that would be a nice loop antenna.
     
  20. AC2FO

    AC2FO Premium Subscriber QRZ Page

    Have modeled several loops horizontally @ 80' with eznec and they seem to produce a lower angle and more gain than a verticaly oriented loop at same height.
     
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