Skyloop Calculator

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KY8D, Mar 31, 2020.

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  1. KY8D

    KY8D Subscriber QRZ Page


    A cute little calculator I made for comparing the trade offs, one band to another, on skyloops of any size, and any shape, no mater how irregular. Free, as always, the source code included.

    Find it here: Skyloop Antenna Calculator
    W7FAL, KK4NSF, EA1DDO and 1 other person like this.
  2. KK4NSF

    KK4NSF Ham Member QRZ Page

    Very interesting..... and useful. I especially like your reason for "why it is free":

    Generosity is not only listed first, but also held to be foremost among Lord Buddha's Six Perfections. Plus there's the fact that nothing sucks all the joy from a hobby faster than the taint of commercial expectations. So I'm earning a wee tiny smidge of good karma, plus also keeping it fun. Reasons enough.

    While I'm certainly not opposed to earning a living, it is nice to see folks using their skills to advance the hobby.

  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    The calculator doesn't agree with NEC2d very well:

    The example posted above generates a five sided loop for 5.332MHz, but doesn't specify a height. I created that loop in AutoEz, assuming #14 Cu wire, five sides each 11.245m long, feed point in a corner, average earth, where the height of the loop is H.

    With H=10m high, Nec predicts Z=130.5-j73 Ohms while the calculator shows 147.6 Ohms with no reactive term displayed. This loop actually resonates at 5.45 MHz, where the Z = 139+j0. To make this loop resonant at 5.332MHz, the side length would have to be changed from 11.245 to 11.47m.

    Here is what happens to R, jX and Swr100 as you change the height H of the loop (with sides=11.47m) from 4m to 20m:


    The loop Resistance changes from 96 Ohms to a peak value of 170 Ohms and then starts decreasing...
    The loop Reactance changes from 30 Ohms inductive to -80 Ohms capacitive, with zero near H=10 (because I lengthened the wires).

    Nec shows the details here. Notice where the peak radiation goes when H<13m. Also notice what happens to Average Gain at low heights:

    The pentagon shaped loop is a bit directional. Here is the elevation pattern at 0 degree azimuth overlayed with the azimuth pattern at 0deg azimuth when H=10:


    You can see from the plot above that it is not a particularly good antenna for DX.

    Not sure what the R and Effic. boxes shown by the calculator show? Just copper losses?
    Last edited: Mar 31, 2020
    K0UO likes this.
  4. EA1DDO

    EA1DDO Ham Member QRZ Page

    Hi Gan, first let me thank you for all your effort placing these cute software free to everyone.
    I would like to ask/suggest something.
    How easy/difficult would be to release this software on any "native" Windows language?
    To install LabView is not a great obstacle but someone might be reticent to do that. If same software were available in "ready to run" format, it could be good idea.

    Don't get me wrong. It is just a question.

    Thank you very much

    73, Maximo
  5. K8JD

    K8JD Ham Member QRZ Page

    Calculate THIS

    Here is an easy one I have done for fullwave loops on 3 different properties I have lived at.
    L in feeet =1004/F in MHz.
    A Single band loop can be fed with 1/4 wave of 75 Ohm coax to a 50 Ohm coax feed of any length to the rig.
    No tuner needed.
    Then get the loop up as high as possible.
    WE4E likes this.
  6. KY8D

    KY8D Subscriber QRZ Page

    Thank you for checking that out. I must investigate via EZNEC, it seems (that being what I have).

    There being no entry for height-above-ground, the formulas employed are instead for free-space. So R(rad) doesn't include ground. If and when I can find a reliable ratio in terms of Lambda for factoring height-above-ground, I will include it.

    All that the calculator claims to do (as I think is stated on the download page) is to combine the generalized formula for Rr of a loop (based on f and area) with the generalized formula for calculating the area of any polygon (literally ANY polygon, no matter how irregular). The only back-checking I did was to compare my calculator's result with that of a published example from the book "LF Today". That and one other, I think.

    For the present, efficiency is simply the ratio of radiation resistance over combined radiation + dc resistance. It is, as yet, without any compensation for skin effect. I'll get to that later. I can steal a module from one of my more elaborate calculators for small loop antennas.
    Last edited: Apr 5, 2020
  7. KY8D

    KY8D Subscriber QRZ Page

    I apologize for the LabVIEW Run-Time Engine being an extra hurdle. But it's all I'm able to do with any efficiency. I could put out similar calculators in Perl, burned as stand-alone *.exe programs. I even have done so in the past. But for these, they being more complicated, the GUI becomes a most burdensome task. Or they are for me, at any rate. LabVIEW makes GUI-writing easy as pie. As time moves along, I hope to supply enough calculators as to make the trouble of installing the LVRTE more worth while.

    Writing LabVIEW just a spin-off from my regular job as a test engineer. There are some aerospace fluid- and pneumo-dynamic formulae which to me (as a hardware guy mostly) seem quite esoteric. And for having to do them regularly, I started writing calculators in LabVIEW for them. Thus to save the tedium of MS Excel. And then one day, I thought, why not also for my radio hobby. And it began ballooning from there.

    That said, if there is a documented formula for antenna design that would serve the community best when put into a continuous loop, then feel welcome to present that concept to me in an email. You'd need to also point out examples. I need those for double checking my work. Give me only just that much, and I'll put it on my to-do list.
    EA1DDO likes this.
  8. AC6LA

    AC6LA Ham Member QRZ Page

    Putting aside his Skyloop Calculator for a moment, I'd just like to give a big thank you to KY8D for starting this thread since it led me to his French Curve tool. Now that is worth its weight in gold. And if you're the type who enjoys such things you might also like this explanation of the math behind spline curves.

    Oh, one last thing. From his QRZ page comes this gem about KY8D:
    Exactly what is needed during these unsettled times; more diversions and more smiles!

    Dan, AC6LA
    EA1DDO and KY8D like this.
  9. EA1DDO

    EA1DDO Ham Member QRZ Page

    Gan, no need to apologize, please.

    I am curious and been having a look and I can see LabView has several option when you create your application;

    I wonder which one you currently use. Perhaps Stand-alone application" ?
    What if you compile or export using "Installer" or even ".NET interop assemblies" ?

    Thank you.

    73, Maximo
  10. KY8D

    KY8D Subscriber QRZ Page

    I have always built stand-alone *.exe files for giving free things away. Not being any manner of Microsoft guru, I have had not truck with any *.NET functionality.
    I switch back and forth between Windows 10 and Ubuntu Linux. Long ago it had been NetBSD, and before then Amiga.
    The thing about LabVIEW is that I use it at work every day. If given a formula and one or two known-good examples, I can bang one of these calculators out in a day.
    Doing the same thing in Perl, I'd have to use Tk for the GUI. That because I've never got around to learning WxWindows. More is the pity.
    And I've started in on trying to teach myself Python a few times, but always get bogged down with a project that I can instead do in Perl.
    Being lazy, using LabVIEW, where the GUI is a breeze.

    You are most welcome!
    Gan (say like John) Starling, KY8D

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