Ferrite Toroid FT240-31

For use in baluns and chokes/isolators. More than enough for UK legal power so perfect for your QRO balun project.  9 turns of RG8mini/RG58/RG316 (400w SSB) or RG142 (1kW CW/Digi) make a great "resistive" balun/choke for 3.5MHz-30MHz.  12 turns and you get a little more choking on 160m although the resistive properties only extend up to 15MHz.  The chart in the second image shows the number of turns and which ferrite is effective at HF frequencies.

The 31-mix is perfect for an all of HF Choke/Balun and our own legal-limit baluns and chokes use this 31-mix core.  We also sell this size in 43-mix (>7MHz), 61-mix (UnUns) and 75-mix (VLF).

• Use: Bands 160m to 10m
• Size: 60.0x35.5x12.7mm, 2.4x1.4x0.5in
• Fair-Rite 2631803802 , 31-mix material

Need help choosing a ferrite?  See our page on selecting the best size/type here.

Toroid sizes/types are easy to ID, the "240" translates to 2.4" (diameter) and the "31" is the ferrite mixture. What type do you need? 61 is used in the G3TXQ CobWebb balun, 43 is good from 7MHz and up (and a good general-purpose 7-30MHz solution) while 31 is better if you use the lower HF bands. Remember, you can stack the cores for increased choking and power-handling. As always, ratings need to factor in the aerial (SWR) match and duty-cycle.

We also sell a snap-on 31-mix ferrite, known as the Problem Solver...