For those who intend to build the FCP INV. L. with a T-200-2 (or an antenna tuner). Me and a few guys from our club wound different types of baluns and chokes on different material and measured them with a analyser. We found the T-200-2 next to useless below 3 Mhz due to a low AL value (uH/100 turns). The T-200A-2 is a lot better, but still not really good in balancing. You better use ferrites (FT-something) as long as you use moderate power.
BUT if you go QRO, you should stick with the iron powder cores. I once replaced the T-200-2 in my homebrew s-match with a ferrite. I changed back the same day, cuz after a few seconds with 750W the ferrite got so hot you would not want to touch it. The T-200-2 runs cool over an entire contest. Next step is to replace it with a T-300A-2. Below you find a list of cores with their corresponding Al Value. You can clearly see that the T-300-2 is even lower than the T-200-2. For the FCP INV L. i think a T-300A-2 or even better a T-400A-2 is best choice, may it be expensive. Core Al Value T-200-2 120 T-200A-2 218 T-225-2 120 T-225A-2 215 T-300-2 114 T-300A-2 228 T-400-2 180 T-400A-2 360 I'm not a technician or rf-specialist and english is not my native language, so please forgive me if my explanations are a bit ragged. Yes, i use a T-200-2 in a tuner, which of course is not the same as an antenna, but my feeling tells me i'm on the right track when i say that a T-200-2 is no good choice for frequencies below 3Mhz, http://toroids.info http://www.qrz.lt/ly1gp/amidon.html -- 73, Martin DM4iM _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
