The attachments on my earlier posts regarding Linux updates were stripped somewhere along the way. So I have placed the attachments for both Linux Mint and Raspberry Pi OS in the following Dropbox location:



These items deal only with the need to mark the STLcalc program file as executable. If you've already done that, there's no need to do anything more.

Curious ... what formula does STLcalc use?

Here is a discussion where the Kraus equation has been found to be incorrect in yielding the loop feedpoint Z.

https://forums.qrz.com/index.php?threads/empirical-evidence-and-the-scientific-method.641240/page-4

Note, the discussion continues onto the next few pages (like page 5) on the QRZ website.

Many websites, many loop calculators still seem to use the Kraus loop equation as the basis for their results.

I have moved on from using loop calculator programs for much of anything any more, preferring to use
real-world measured 'data' using the now ubiquitous antenna analyzer we all have in our possession.

73,
de Jim AA5CT

Hello Jim,

Curious ... what formula does STLcalc use?

STLcalc uses the formula presented in the 24th edition of the Antenna Book, and that is based on the Kraus equation as you have have noted. I keep the loop length, including the loop conductor, the capacitor body, and any jumpers needed to connect the cap to the loop under 30% of the wavelength at the design frequency, and usually closer to 25%.

For a single turn small loop I have found the formula to be reasonably accurate. A coupling loop length of approximately 1/5 the length of the main loop (which results in a 25:1 impedance transformation) results in good match to 50 Ohms. The linear measurements (length, diameter) are convenient to use, but the actual transformation is based on relative areas of the loops, so loop shape is a factor as well.

I don't use transformers for two reasons: 1) It is a single-band solution, so primary turns switching is required for band changes; 2) The transformer has to be very beefy to handle even modest power levels, and I design for QRO levels. Many pounds of ferrite and $$$ involved.

For multi-turn loops, the calculation of Rr needs to be modified because the equation assumes that the additional turns are the same size as the single turn, so the overall conductor length is greater, and that's a different antenna. STLcalc holds the overall loop length constant, so the area is shrinking with each additional turn. To compensate it is necessary multiply the calculated Rr by the number of turns. The coupling loop relationship is still is the 1/5 range if the coupling loop is physically placed at the loop midpoint [opposite the capacitor for an odd number of turns, adjacent to it for an even number of turns].

Here is a discussion where the Kraus equation has been found to be incorrect in yielding the loop feedpoint Z.

How are you measuring the feedpoint impedance? Are you and the instrument you are holding becoming part of the measure value?

73,
Gus Hansen
KB0YH

Sigh.

I've got what I need to know.

IF you read through that thread (doubtful you did, and understanding, comprehending being
the next step up) then I need not add any more.

Thank you for your response.

73,
Jim AA5CT

Owen Duffy has made numerous posts about loop antennas on his site and has developed several loop calculators.? He recently wrote a review of STLcalc 2.05 .



Roger

"Here is a discussion where the Kraus equation has been found to be incorrect in yielding the loop feedpoint Z."?? - quoting AA5CT


Kraus calculation is not wrong.? The poster has made an unfortunate error.? Respectfully, it is naive to think that since a transformer can be made to obtain a 50 ohm match with a given turns ratio, that the resulting resistance reflected across the transformer (in this case roughtly 22 ohms) is therefore the radiation resistance of the antenna.? The impedance at the match point is a combination of things and if resonant it is still the combination of many sources of resistance all rolled together as an apparent match resistance.? So, to list these, and this is probably not an exhaustive list, they include;

1. Construction losses: ie mechanical connections on the loop conductor and to the tuning capacitor, dielectric losses in the capacitor, core and conductor losses in the transformer, radiator conductor loss which is determined by material type and skin depth at the operating frequency. etc. etc.

2. Losses from energy coupled into lossy earth and nearby lossy conductors in the near field of the antenna.? This can easily be observed and I have seen it with earth which goes from thaw to frozen and back to thaw where the resonant match changed due to freezing and returned to the previous value in spring. Proof? for anyone who suggests that so called magnetic loops are not subject to ground losses, that the truth is otherwise. Similarly, if you use collapsible poles to raise/lower the antenna the match and therefore turns ratio needed will be seen to change.? This is ground loss rolled into the match.

3. Radiation resistance.? This is a function of the enclosed area of the loop and can be mathematically calculated and is independent of the feed method and point along the antenna which is chosen for feeding energy into the antenna which was claimed in error by Ben Eddington G0CWT

Hi Frederico

The losses impact the antenna's efficiency which is a reciprocal thing ie it affects both TX and RX, however on RX we often use very low efficiency antennas, especially when we want a broad band antenna, if it is small it is automatically inefficient (if it is broad band), but the thing is modern recievers have excess gain for HF especially the low end of HF so we can disregard the efficiency problem for RX as long as noise level increases when the antenna is connected.? Of course a highly efficient antenna will always bring stronger signals but you get the point.

Best regards...Joe

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