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broadband balun using coax

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goldensol

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stackpole balun core

I want to disign broadband balun using coax.the frequency up to 400MHz ,
power up to 200W.Could you give me some advise to select the ferrite.
 

flatulent

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several sources

Stackpole company makes ferrite in shapes specially suitable for baluns. In general the two cylinders in parallel work great. Fair-Rite company has an application note describing the effects of their core materials.
http://www.fair-rite.com/Broadband.pdf
Their catalog at http://www.fair-rite.com/products.htm will also have selection guides.

In general the high frequency end is set by the coax length and the low frequency limit is set by the ferrite type. You should experiment to pick the trade off between impedance accuracy and bandwidth. There are two tricks to extend the frequency range a little. Shunt capacitors will extend the high end and series capacitors will extend the low end. You will have to use a network analyzer to get the right values.
 

g579

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Thanks for the Fair-rite link. Should be a good alternative source. Their app.note is fine about this topic.
 

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