On Thu, 31 Jul 2008 09:10:54 -0700, Alan Bloom wrote: >When you wire two chokes of different value in series, you almost always >get a series-resonant "hole" in the attenuation somewhere between the >parallel-resonant frequencies of the two chokes. It's not hard to see >why that's true if you model each choke as an ideal inductor in parallel >with a capacitor.
But that's not an accurate model! If ferrite chokes are wound on the "right" ferrite material (the mix), they have a dominant RESISTIVE component in the frequency range of interest. While it IS important to consider the series L-C possibility, in REAL chokes, the resistive component can prevent this from being a problem. Indeed, this goes back to the original comment that the important property of a ferrite choke is RESISTANCE, NOT inductance! A properly designed choke (that is, right number of turns, winding style, and using the "right" material) can be made to have a high resistive impedance over at least an octave, and Fair-Rite's #31 is good for at least two octaves. Again, see my tutorial, which also shows how simple curve fitting in a spreadsheet can be used to come up with actual R, L, and C values from magnitude-only impedance data. It also shows a method of measurement that is much better than commonly accepted "standards," like the HP Z meters and network analyzers when the unknown Z is high. 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
