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Balun or No Balun on 80 meter loop?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KC8PJS, Nov 14, 2009.

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  1. KC8PJS

    KC8PJS Ham Member QRZ Page

    Hello,
    I am just starting to get into HF and need to build some antennas to work with it. I have surfed around and have come to a conclusion that with my space requirements and all I am going to build a 80 meter full wave flat loop and a G5RV. Both will be about 25-30 feet off the ground supported by fiberglass masts around the parimeter of my city property. They will be seperated from each other to minimize possible inductive interference with each other. They will both be fed with RG-8 coax about 35 feet on each (plus 33ft 450 ladder for G5RV).

    My problem is that in all my reading nobody agrees on the use of baluns. Most articles say I should use a 1:1 choke balun or a 4:1 current balun on the G5RV, but it's split as to the loop. So, risking more indecision, what if any balun should be used on a 80 meter full-wave (horizontal) loop fed with RG-8 coax?

    Thanks, Kevin KC8PJS
     
  2. NA0AA

    NA0AA Ham Member QRZ Page

    I'd go no balun, but then I'd also go 450 ohm open wire so that I could tune the loop for more than 80 meters.

    If you choose a balun at the feedpoint I suggest a choke balun, 1:1 not a voltage balun.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If you have an 80m loop, what's the G5RV for?

    If you can list a good reason to have both, please let us all know.

    An 80m loop tuned to 3.5 MHz is also resonant on 7.0, 10.5, 14.0, 17.5, 21.0, 24.5 and 28.0 MHz, so it will be resonant on six ham bands, and fairly close to resonant on two more. That's the whole advantage of a loop, it's resonant and thus easy to match on all harmonics, odd and even.

    I cannot envision any circumstance where the G5RV would work "better," so that's why I asked the initial question.

    You can use a 1:1 balun on the loop, but it's questionable whether that would actually improve anything or not. It shouldn't hurt, because it will not be looking into much of a mismatch on any band (probably 3 or 4 to 1, but nothing gross and nothing that will raise balun losses much, or even feedline losses much).

    You'll need to use a tuner anyway, and unless your coax run is very long there shouldn't be much coax loss, so I'm not sure what the advantage of going to ladder line would be. Coax loss can get gross when VSWR >10:1 or so, but you shouldn't ever see that on six bands, and probably not even on the other two bands (30m and 17m).

    What's the purpose of using the G5RV?
     
  4. KA5S

    KA5S Ham Member QRZ Page

    Do you need to suppress common-mode current?


    Cortland
    KA5S
     
  5. W7IVK

    W7IVK Ham Member QRZ Page

    loop

    absolutely no baluns on loops they dont need them
    check the 94 arrl handbook
    loops load up with ladder line or coax with a tuner just fine without a balun
    i have a loop cut for 80m @ 30 ft fed with coax and i have worked the world with it. tunes up for all bands with tuner
     
  6. G3TXQ

    G3TXQ Ham Member QRZ Page

    One thing, at least, is clear: if you use a G5RV you should not use a 4:1 balun - it must be a 1:1 current balun.

    The ladderline presents an impedance to the coax section which is a moderate (not great) VSWR on some bands; on those bands the coax losses are tolerable. The last thing you want to do is divide those impedances by 4, increase the VSWR, and increase the coax losses!

    73,
    Steve G3TXQ
     
  7. KC8PJS

    KC8PJS Ham Member QRZ Page

    G5RV use

    I was turned on to loops by a fellow ham who has worked HF for a while now. He has a 160 meter loop and a G5RV. He says that there are a few bands that they each don't tune very well but the other does just fine. That was my initial reason for the G5RV. I, of course, do not have room for 500+ feet of wire on my city lot, so I decided to go with an 80 meter loop instead. From the posts above it seems like the 80 meter loop may do everything I want just in itself!
     
  8. R3BU

    R3BU Ham Member QRZ Page

    Here in Russia a one wave loop for 80m band is widelly used.In a free space it has 110-130 ohms.At the hights of 0.15-0.25WL(12-20meters) with paralel to the ground configuration the antenna turns to be like TWO ELEMENT QUAD with main lobe up to the sky.In a short distances, up to~1000miles it will be "bending the needles of S-meters".And It's rezistance may become close to mentioned "two el quad" in 70-90ohms or close.On 40m and 20m bands the main lobes will begin to have low angles to horizon-just what we need for DX hunting.But the rezistance will rize to uncomfortable to us values 150-200ohms.And to get rid of the radiation of the coax cable's breid it is recomended to make 10-15 turns by the coax on ferrite ring of appropriate size near the feed point.To use exstra balun 4:1 is a question of the owner of antenna...
    And located close to the ground, at hights less then 10meters on 80m band It may begin to have again bigger rezistance,thanks to added ground loss rezistance.
    P.S. Some Hams to feed their loops use short ladder lines with simm. tuner. The result is the best match on all bands without losses in the feeding line.
     
    Last edited: Nov 14, 2009
  9. AD5ND

    AD5ND Ham Member QRZ Page

    I've fed 1wl loops with RG-58, RG-59, RG-11, twin RG-6 and twin lead. I've never used a balun. This isn't to say a balun isn't necessary. My preference has been the twin RG-6. My rigs have all been tube type with Pi networks. If I had the money an automatic tuner at the feed point of the antenna and the best coax money could buy would be the preferred method.
     
  10. K8JD

    K8JD Ham Member QRZ Page

    I have loops for 40 and 30M, feeding with 1/4 wave sections of RG59 and splice to RG8x to reach the shack. the QW sections match the loop's Z to 50 ohms for the long coax run to the shack. This method eliminates need for a tuner and minimizes feedline losses
    I have enough other antenna systems for the other bands I work so the loops are designed monoband only.
    I recently refurbished the antennas and relocated them, so I took the opportunity to install some MFJ 1:1 baluns. I figured if they dont help, they should not harm much.
    The balun assemblies have hanging loops and a nice SO239 connector, maybe the main benefit, so I can hang up the feedpoint on a tree limb.
     
    Last edited: Nov 15, 2009
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