Topband: T-200 vs. T-300

[Martin]

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

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73, Martin DM4iM