Big Loops. What is the point of diminishing returns?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K0MBT, Nov 30, 2018.

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  1. K0MBT

    K0MBT Ham Member QRZ Page

    For those of you hams who have built big loops. What do you find is the point where more wire reduces signals, both being transmitted and maybe received.

    I have had my 1000 foot loop running for about a week. It's performance seems good on every band I have tried it on using A/B testing. It could easily be expanded and have another 1000 feet of wire. I made a 4:1 current balun and coax into the shack.

    My other antennas are a 40 m horizontal delta loop and have had dipoles in 10-20 and 40 meter tunings although only the 40 is being currently used.

    Obviously this question isn't for everyone.
    73
    Dave
     

    Attached Files:

    Last edited: Nov 30, 2018
  2. NH7RO

    NH7RO Ham Member QRZ Page

    I'm going to throw in my educated guess; a 160m full wave length (@560 feet or thereabouts). Too many lobes, unpredictable nulls and hard to match beyond that.

    Sometimes it's best to quit while we're ahead (at Vegas or on the antenna range),

    73,

    Jeff
     
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  3. WB5WPA

    WB5WPA Ham Member QRZ Page

    What Jeff said - ya start getting lobes and such ...
     
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  4. KK5JY

    KK5JY Premium Subscriber QRZ Page

    Also keep in mind that as you change the size and shape of a wire loop antenna, especially one that is close to the ground with respect to wavelength, the nulls that get added or removed aren't necessarily (just) horizontal.

    There's also the issue of how well the loop of a given size matches the feedline.
     
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  5. AI3V

    AI3V Ham Member QRZ Page

    I would put up a second random loop and means to switch between them.

    Unless you make the loop into a rhombic, you will have little control over where the peaks and nulls point.

    Making the loop bigger always makes the lobes stronger, which is great if the lobe points where you want to talk.

    I used rhombics at the navy relay station on Diego Garcia, and random big (500ft or so) camping in the national radio quiet zone.

    Rege
     
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  6. KI5FJ

    KI5FJ Ham Member QRZ Page

    Dave, I used a corner fed 480 Ft horizontal loop that was up 35 Ft for about 18 years.
    The lobes are predictable. On 12-Meters modeling predicted a massive 14 dBi lobe pointing at the South Pacific. Sure enough I was often called by VK, ZL and JAs.
    The nulls were never a problem. If I could have moved the feed-point to mid-way on a equal leg length square loop, the gain lobes would be nearly the same amplitude. I suggest you consider the shape, height and feed-point location of your loop. If you are interested in 630-Meter band, 2100 Ft is 1 wl. I used home-brew open-line from the loop to the Earth and then a Balun to 150 Ft of 7/8 Inch Heliax. The In-the-Shack SWR was best on most bands with a 1:1 Current Balun. Your best ratio may be other than 1:1. Lightning protection is a must have item. I would disconnect the open-line during thunder-storms. Be warily of comments from those who have not actually erected a large loop! 73 Joe O, K I 5 F J, NNNN
     
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  7. WB5WPA

    WB5WPA Ham Member QRZ Page

    re: "Making the loop bigger always makes the lobes stronger,"

    AND the trade-off, of course, is, the nulls become deeper, or more numerous. There IS that down side that no one 'talks' much about ... in situ, I don't think a lot of ops *know* when their antenna is nulled in a particular direction, band fades kind of 'cover up' or mask those facets of operation.
     
  8. W8EJO

    W8EJO Ham Member QRZ Page

    I once had a 500+' loop. Excellent antenna.

    I tried modeling it with 2 feed points that I could switch between in order to "rotate" the peaks & nulls. It might be possible but I never got it done.

    Terry
    W8EJO
     
  9. AI3V

    AI3V Ham Member QRZ Page

    I can say with pretty good certainty that my camping loop has a lobe on Detroit/Windsor, and a null at Western Europe,

    All my cqs were answered in that direction, and I seemed to be one of very few stations answering cq,s from South east asia, yet trying to even hear the Europeans was tough.

    Rege
     
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  10. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Your 1000' loop is almost 2 wavelengths on 160 and 4-WL on 80m; I'd think "going bigger" is unlikely to improve anything unless you want to fool around on the new LF bands.

    If it were me, rather than going "longer," I"d do everything possible to go "higher."

    I had a 520' loop at 40' AGL many years ago back in NJ, used mostly for the November SS contest where "DX" was unimportant but having a potent signal Stateside on 80 & 40m was. For that, it worked extremely well; we had beams for the higher bands and never used the loop above 40m. No obvious deep nulls were observed on those two lower bands at that loop elevation. I think nulls become more pronounced not only on the "higher bands," but also as the loop elevation above ground is dramatically increased.
     
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