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?