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1:1 Choke Toroid Question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N1MVP, May 30, 2021.

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  1. VK2TIL

    VK2TIL Ham Member QRZ Page

    Like W9IQ, I have attempted to demonstrate the relative values of u' (the real part of the complex permeability that contributes to reactance) and u" (the imaginary part of the complex permeability that contributes to loss) in graphical form.

    I re-drew the Fair-Rite permeability data on semi-log scales;

    31, 43 & 61 - Real Part.gif

    31, 43 & 61 - Imaginary Part.gif

    Whilst the inevitable self-resonance of the choke will alter the above simple relationships, the superiority of #31 is evident.

    Attached Files:

    WA7ARK and W1PEP like this.
  2. EA1DDO

    EA1DDO Ham Member QRZ Page

    Have you measured those chokes?

    I've done it and my results match G3TXQ's tables.
    61 mix shows best performance at VHF bands.
    43 mix is best from 21 Mhz up to 50 MHz.
    31 mix best from 1.8 up to 14 MHz.

    That is what I can measure with my VNA.

    73, Maximo
    Last edited: Jun 1, 2021
  3. VK4FUQ

    VK4FUQ Ham Member QRZ Page

    G'day all, a couple of things that I don't really understand! If 61 mix (ui 125) is best at VHF frequencies then why is it used in every ferrite rod coil antenna in every AM/MW radio?

    In Sevick's 'Transmission Line Transformers 3rd Edition, there was no real discussion on the different ferrite mixes for different frequency ranges, but only discussion and loss profiles for the different ferrite material permeabilities with his measurements suggesting that ui's below around 290 were best! Sorry I just don't get it! Regards, Felix vk4fuq.
  4. VK2TIL

    VK2TIL Ham Member QRZ Page

    " ... with his measurements suggesting that ui's below around 290 were best ..." as might be expected in a book entitled Transmission Line Transformers.

    Transformers are not chokes; the requirements are quite different.

    #61 ferrite has almost zero loss (u") up to about 7 MHz; it therefore has high Q over that frequency range and
    is very good for efficient tuned circuits such as BC/low HF radios.

    The aim of a choke is to introduce loss, ie resistance; #31 & #43 have greater ui than #61 and, following the basic physics of ferrites, have greater loss/resistance at lower frequencies.

    There seems to be a widespread misunderstanding of Dr Sevick's work; he studied transformers, not chokes.

    EA1DDO and VK4FUQ like this.
  5. 2E0VSS

    2E0VSS Ham Member QRZ Page

    Ai6RW, Richard Wheeler Choke Balun
    Or Anything Jim Brown or Owen Duffy promotes...

  6. WB2UAQ

    WB2UAQ Ham Member QRZ Page

    Another observation is that Sevick's applications described in his transmission line transformer book are at low impedances. Many amateur radio applications are pushing much higher and above what is recommended.
  7. W1VT

    W1VT Ham Member QRZ Page

    Jerry Sevick's R&D essentially stopped when he retired and no longer had access to the lab gear he needed for making measurements.

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