Thursday, December 4, 2014

A helpful chart for determining resonance of RF Chokes

Hi. I would like to share with you a reference that I have found helpful to keep near the bench. This is a chart for determining the range of resonant frequencies that can be expected for a given inductance value. I keep a copy of it stored with my other favorite RF design tools & software shortcuts. I recommend printing off a copy to keep near your workbench or tack to the wall.

The chart is from a book called "Solid State Radio Engineering", not to be confused with the infamous "Solid State Engineering for the Radio Amateur" by the two greats W7ZOI & W1FB. Rather the originating book was written by Krauss, Bostian & Raab.

"Because of distributed capacitance between turns, every RF coil behaves like a parallel LC circuit and exhibits a self-resonance frequency above which its impedance is capacitive. Since RF chokes are used to provide high impedances, it is important that the operating frequency be less than the resonance frequency. They are made in a variety of forms on phenolic, iron, and ferrite cores, and their resonance frequencies and Q values vary widely."

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I hope that this chart is helpful to you.  I'm constantly working on my method of circuit design & construction, often discovering a new tool or reference that helps me achieve more complicated tasks or calculations quicker or more efficiently. I look forward to sharing these resources and other tips and tricks with you here on the Freestate QRP blog. 

Do you have any handy tips for determining values of critical circuit components? What type of RF Chokes do you use and for what applications? . The combination of ferrite beads Do you 'Roll Your Own" or do you prefer the small molded or encapsulated ones? Please share your thoughts with us! 

Would you like to see more resources like this chart? Would you rather see posts on free &/or open source RF design tools? Feel free to email freestateqrp at gmail and let us know your opinions. Alternatively, share your feedback as a comment to this post.

Thanks and 72/73.