Empirical evidence and the scientific method

Discussion in 'Amateur Radio News' started by VK6FLAB, Jan 5, 2019.

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  1. WB5WPA

    WB5WPA Ham Member QRZ Page

    Why is this relevant?

    Because practically every loop calculator on the planet uses the same formula to calculate an incorrect feed point Z.
     
  2. KQ6XA

    KQ6XA Ham Member QRZ Page

    Try 4nec2.
    It calculates the correct feedpoint Z of a loop.
    It is free on the planet.
     
  3. WN1MB

    WN1MB Ham Member QRZ Page

    But he didn't specify which planet, now did he?
     
  4. WB5WPA

    WB5WPA Ham Member QRZ Page

    Nein.

    If fail like the rest.

    More later - have a new noise maker on 160 I have to track down first!
     
  5. KQ6XA

    KQ6XA Ham Member QRZ Page

    GIGO.
     
  6. WB5WPA

    WB5WPA Ham Member QRZ Page

    Here's the part where Kraus is wrong, and, apparently every loop calculator follows this formula (notice, Kraus himself is choosing a Lambda/3 circumference loop for a numerical example below):

    Kraus_Section_6-9_eq_8_9.jpg


    The real, measured loop impedance comes out to be around (for a Lambda/4 circumference loop) about 22.5 Ohms. I'm thinking that KK5JY found his loop to be more like 50 Ohms (thereabouts) on a Lambda/3 circumference loop. Another ham here on the board I exchanged info with also came up closer to my values for a 6 meter (I think it was) Lambda/4 circumference loop.

    Added: Ben Edginton also found the 22 point some-Ohm value. Here is his story on this subject:

    http://www.g0cwt.co.uk/magloops/new_page_2.htm
     
    Last edited: Jan 8, 2019
  7. WB5WPA

    WB5WPA Ham Member QRZ Page

    Revised -

    Even Ben was taken-in by the errors propagated throughout the years on this. Here's an entry from his website on this subject:

    My first attempts did not work I had taken information from the ARRL Antenna book which told me that the radiation resistance of the loop would be less than 0.1ohm on 80 metres and I took this to be the feed point resistance as it appears does every one else I have spoken to .

    At 50 ohms to 0.1 the impedance ratio is 500 to 1 this means the square root of 500 = 22.36 so the transformer would have to be 22 to 1 . turns ratio.

    I first located two ferrite tubes that I thought would be suitable and put them side by side and used two copper tubes to make the secondary 1 turn winding ,using two end plates made of copper clad board I then wound 22 turns of wire through the center to make the primary winding .

    I now had my 500 to 1 impedance ratio transformer I connected it in series with the remotely controlled tuning capacitor and the 64 foot of wire loop that I had pulled up the 25 foot mast.

    I went down to the transceiver and tried to tune up on 80 metres , no chance not even a hope checked everything and tried again no possible SWR reading .

    I decided that the problem was the matching transformer but how to find out ,well I began to reduce the number of turns on the primary winding and found that when the turns where reduced the SWR began to show results but it was not until the primary was down to 2 turns that I could get anywhere near to a 1 to 1 swr.

    From: http://www.g0cwt.co.uk/magloops/new_page_6.htm
     
    Last edited: Jan 8, 2019
  8. KQ6XA

    KQ6XA Ham Member QRZ Page

    You haven't spoken to the right people yet :)
    Radiation Resistance is not the same thing as Impedance at Resonance (especially not for small in terms of wavelength antennas).

    If you would like to expand your knowledge about it, Wikipedia has a fairly good treatment on it, at least on today's version of the page:
    https://en.wikipedia.org/wiki/Radiation_resistance
     
    Last edited: Jan 8, 2019
  9. WB5WPA

    WB5WPA Ham Member QRZ Page

    Here is an example of a popular loop calculator on the interwebs that yields an incorrect result too:

    LoopCalc_66pacific-com.jpg

    Note the Radiation resistance value. Add that value to the AC resistance (Loss Resistance) value of 10 ga. copper used above and one *still* comes off a calculated factor of 10 lower than the measured Loop feedpoint Z values.

    This calculator (http://www.66pacific.com/calculators/small_tx_loop_calc.aspx) is presumed to use an equation near to being the same as the John D. Kraus equation as detailed further above.
     
  10. WB5WPA

    WB5WPA Ham Member QRZ Page


    And I quote, again, from Kraus:

    This is the radiation resistance of a small single-turn loop antenna, circular or square, with uniform in-phase current.

    Those words are plainly visible on my monitor, how about yours?

    Can you yet explain why Kraus is in error, why his equations don't match reality? Time and time again, as measured by different 'operators'? Not just a 'case sample of one'. Maybe you missed those points. Four different individuals by my account, now. Maybe you didn't glean that from all the foregoing? These 'things' are simple enough to measure today with something commonly known in the amateur community as ... antenna analyzers. They even show up all the time on the swap-meet forum on this website!


    .
     
    Last edited: Jan 8, 2019
    N2EY likes this.

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