Bifilar wound ferrite rod filament choke -- Performance results

Discussion in 'Homebrew and Kit Projects' started by SWL37632, Aug 22, 2021.

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  1. SWL37632

    SWL37632 QRZ Member

    I've seen a bifilar wound ferrite rod filament choke used in 811A/572B GG amps for decades....ARRL handbook, Orr, etc.

    Since I'm in process of a 2 x 572B GG HB build and testing for 20m, my question is: Is there any hard test data for this kind of bifilar ferrite rod filament choke which shows: a) Common mode RF choking effectivity/performance ? b) Differential mode RF choking effectivity/performance?

    I'm looking for hard test numbers and have researched this but haven't found any authoritative resource.

    Thanks in advance.


    20+ WPM 1970's Extra
  2. K0IZ

    K0IZ Ham Member QRZ Page

    I can't help you with the specific test numbers you are seeking, but my newly finished (2) 813 GG amp for 20 meter used a 23 turn bifilar 14ga on 1/2 x4" type 61 core. Measured 29 uh. I pre-tuned my pi-net input with my nanoVNA and was satisfied with 1.06 to 1 with 130 ohm resistor to simulate filament impedance. When I connected the choke, no change in SWR or reactance. So I figure the choke was doing a really good job. John.
    N2EY and SWL37632 like this.
  3. SWL37632

    SWL37632 QRZ Member

    Thank you for your information.


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