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To compare differences by manufacturer consider Palomar's type 43 material is good for attenuation from 2 MHz to 1000 MHz. Fair-Rite's type 43 is good for attenuation from 20 MHz to 300 MHz. As you can see this is significant on the HF band. To compare differences by manufacturer consider Palomar's type 43 material is good for attenuation from 2 MHz to 1000 MHz. Fair-Rite's type 43 is good for attenuation from 20 MHz to 300 MHz. As you can see this is significant on the HF band.==RF Current Flow==Fair-Rite 31 material - the best grade for general purpose HF and low-band chokes. Fair-Rite 31 clamp-on core, Part No 0431177081. An HF ferrite choke will typically need 6-8 turns passing through the center hole. Regardless of the type of core, one pass will probably not be very effective. The same Fair-Rite 31 material is also available in a "FT240" 2.4-inch toroid formatFair-Rite Part No 2631803802. 10-12 turns of coax on a FT240-31 makes a nice low-bands choke or balun. ==Fighting RF Current Flow==Air-wound chokes are one of the least effective ways to stop common-mode current. They are also targeted to a narrow band because the way the winding is done dictates what band it will be effective on. They are cheap and easy to implement but have the aforementioned deficiencies. Strings of ferrite beads may also have less effect at eliminating common-mode current. They are easy to employ and do not suffer from the narrow band shortfall. However, it takes a lot of ferrite beads to have much reduction impact and this can become expensive. To have the most effective reduction of common-mode current you must employee ferrite cores of the specific mix for the application and use multiple turns. The best ferrite cores are made in the United States such as those made using Fair-Rite 31 and 43 grade materials. The best performance comes from large cores. The problem with this approach is cost. This is a very expensive way to deal with common-mode current.