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Low pass filter toroid core material.

Discussion in 'Homebrew and Kit Projects' started by OK3RIC, Mar 7, 2021.

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  1. OK3RIC

    OK3RIC Ham Member QRZ Page

    I want to build bank of shortwave LPF's for my linear PA (100W), but I'm confused about inductors core materials. From my perspective is ideal to use Amidon's iron powder #2. Based on datasheet it: "Offers high 'Q' for the 2 MHz to 30 MHz. frequency range". So such a material is possible to use for every shortwave band. But in lot of kit's and DIY designs I saw that for frequencies higher then 7 MHz everybody use material #6. Then I tried to search which material's are used in ICOM IC-7610 (IC-7300). In service manual I clearly see #2 for low frequencies but for example for 20m band they use even material #10. Which looks to me total out of material specification. I'm really confused about it. Can somebody explain to me, how can I choose optimal material?
  2. W1VT

    W1VT Ham Member QRZ Page

    I used to wind a couple cores and measure the Q values. Then I'd choose the one with the highest Q.
    At the time that was easier than calculating the Q as I have an HP Q meter at work.
    As I recall I've used type 6 as low as 80M to obtain a Q of 400.

    Zak W1VT
  3. K6BSU

    K6BSU Ham Member QRZ Page

    The Amidon toroid type 2 (red core) and type 6 (yellow core) will cover the entire HF spectrum. #2 for 160M up to about 30M. Then #6 up through 10M.

    There is considerable overlap in the "Q" curves, so there is no specific break-point choosing between these two mixes.
    KJ7RDV and OK3RIC like this.
  4. OK3RIC

    OK3RIC Ham Member QRZ Page

  5. KX4OM

    KX4OM Ham Member QRZ Page

    The Q-curves page is interesting, but it does not provide data on the materials regarding inductors with fewer turns such as transformers used in antenna or transmitter applications.

    For more info, take a look at the information on iron powder cores here:

    Page 1-11 shows Q curves for Material 6 with some slightly larger wire sizes and fewer turns.

    Page 1-09 is the AL values for iron power cores that are the basis for several online calculators of inductance per turn.

    Page 1-41 has tables for power dissipation vs. temperature rise for Material 2, and frequency ranges for several iron powder materials.

    Ted, KX4OM
    KJ7RDV likes this.

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