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. WA7F

    WA7F Premium Subscriber QRZ Page

    Good info. Thank you!
     
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    1 wave length is about as good as it gets.

    Good Cloud warmer and worm harvesting for fishing.
     
  3. K0MBT

    K0MBT Ham Member QRZ Page

    I would guess you are about right 1 wavelength doesn't have much of a takeoff angle.

    Yesterday worked Fairbanks AK Caracas Venezuela and Italy with phone on my 1200 ft steel loop working with the 10 watt microbitx. The a loop is 5db quieter than our 80 meter loop and about 8-10 db quieter than a dipole.
     
    KA9JLM likes this.
  4. AA7EJ

    AA7EJ Ham Member QRZ Page

    "I would guess you are about right 1 wavelength doesn't have much of a takeoff angle."

    No need to neither "guess or about" - antenna modeling (software) should convince even person form "show me state ".
    The (free) tool is here, let's use it.
     
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    Unless his name is Rege!
     
    WN1MB likes this.
  6. K0MBT

    K0MBT Ham Member QRZ Page

    Su

    It is pretty easy to measure a 40m antenna to within an inch. but this is a beast of a different color.

    I have looked at modeling and frankly once the antenna is this big and in the real world, it isn't going to be like what you see in the graphs. there is a marked variations in dimensions and lay out. We put it into trees with a crossbow. It ends up where it it ends up. Hard to get a perfectly accurate shot with the bolt trailing a string that is dragging along. This loop is about even with the horizon but the uneven ground goes over creeks and ravines, the contact with trees distorts the runs a lot. and the near field is quite slanted. Ivory towers get pushed aside.
     
    WN1MB and K6LPM like this.
  7. AA7EJ

    AA7EJ Ham Member QRZ Page

    I like folk wisdom - in this case "don't sweat the small "stuff".

    Beside - we are all getting off the original post question.

    Technically , and the modeling proves it (again) , the bigger / longer the loop , more nulls and lobes of diminishing intensity - still working with same source / input. But on HF we are at the mercy of ionosphere and it does not stay still.

    Put in another way - longer/ bigger the loop - more it will resemble 1/4 wavelength vertical which radiates equally poorly in all directions. ( another sarcastic folk saying - for the slow pupils in this class )

    My favorite analogy - the higher the (HF) antenna (Yagi) , LOWER take-off angle of the main lobe with lesser energy and MORE energy for side lobes warming the clouds.
    If the user realizes this - he has a choice. If user choice is to be ignorant....
    In other words - optimum height of the antenna is 1/2 wavelength.

    Optimum length of horizontal loop - primary limited by space / height available.
     
  8. K6LPM

    K6LPM Ham Member QRZ Page

    nevermind
     
    Last edited: Mar 23, 2019
  9. K6LPM

    K6LPM Ham Member QRZ Page

    I remember being told as a kid that the beauty of a true "Longwire" (not to be confused with random wire) was that the Longwire was so versatile for multiband performance and didnt require much of the power sucking transformation, baluns, antenna tuners or matching networks. Given enough length the RF would seek its own resonance. This is of course the days before solid state transcievers and transmitters had tank circuits with loading. The seeking its own resonance also might have been an oversimplified statement especially as it was being explained to a twelve year old like I was when I came to understand this phenomena. Later years I pondered maybe it was that if enough wire was strung out that it might be purely resistive in function and hence appear self resonant???
    Ok just was pondering something out loud..... Yes back to the original point of discussion and what aa7ev has pointed out as we get bigger and bigger in loop diameter the nulls and lobes grow ever increasingly more frequent but at a diminished intensity due to the fact that there is only so much rf being applied by the source at the feedpoint. You cant get more of something if there is only so much! Or as he has put it into perspective it performs equally poorly as a 1/4 wave vertical.... But is that a good enough answer or analogy? I dont have the burning desire to learn the modeling software badly enough to explore. i would have a tendency to assume the same as K0MBT getting into such large dimensional wire antennas strung over such diverse terrain and inconsistent substrates with haphazard height isnt going to be so easy to communicate or input into the modeling program. Or as another folk wisdom may put it,,, Crap in, feces out.... Ok there is too many variables, to make an accurate assessment as to exactly what point of diminished returns on that loop? But at some point it becomes similiar to a 1/4 wave radiator ? I wonder why a 1/4 wave and not say a 5/8ths wave? I think more accurately to say it becomes simply an omnidirectional radiator! Well hotdamn! Now we are getting somewhere and this is indeed an advantage of a multiwavelength loop! it no longer is firing straight into the ground and up into outer space, but now its omni and just as it radiates equally poor in all directions it can very well radiate equally well in all directions. So maybe if we can utilize this characteristic to advantage? Perhaps given enough wire, we possibly are able to minimize the effects of a very big variable that many hams without artificial optimized man made support structures (towers vs trees) are able to control.... that is the issue of consistent and adequate height to maintain the proper wavelength above the ground. Also the variation of ground conductivity. Something I suspect modeling usually will make assumption (oh crap! not that again). So if we continue to ad length and the lobes and nulls continue to spring up and spread throughout the greater distance of wire , what happens to that other plane or axis?The take off angle of those lobes? Does it work out equally that those of that plane must share in their energy distribution? Would more wire bring it down lower, as say a 5/8 compared to where it was once comparable to a 1/4 wave, huh?
    I know the previous statement was to make the point of it being similiar to an omni and not specifically a 1/4 wave, but it does indeed spread out the pattern by virtue of squashing those near vertical incidence lobes.
    The question begs for answer more now than ever at what point or multiples of wavelength do we exhibit an advantage of lower radiation angle at lower than half wavelength radiator height and at how many multiple wavelengths does it take to cause enough reciprocation that the ground just no longer makes a big enough difference? Where do we diminish the return to the point that size no longer matters or we are just too bookoo , too bookoo and me no luv ya long line?
    Also how many licks does it take to get to the center of a tootsie roll lollipop?
     
    NH7RO likes this.
  10. K6LPM

    K6LPM Ham Member QRZ Page

    Brian you are a weirdo!
     
    NH7RO likes this.

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