Ron D'Eau Claire wrote: >> >>They also didn't do much except make us feel better. Ferrite core chokes >>actually DO something useful. The cracked balun was poorly designed, so >>it overheated. That's a DESIGN mistake, not a "defect" of ferrite cores. >> >>73, Jim K9YC >>
>Why would you think that? Properly designed, an air core balun and a >ferrite core balun are electrically identical. > That simply isn't true. Air-cored chokes are reactive in impedance, narrowband and easily detuned. A properly designed ferrite core choke is predominantly resistive and broadband, which makes it a much more dependable solution. Steve Hunt G3TXQ has measured a wide range of different chokes and plotted the results on a graphic that shows this point very clearly. <http://www.karinya.net/g3txq/chokes/> In Steve's graphic, an effective choke needs the largest possible bandwidth of dark green, preferably with the black underline denoting predominantly resistive impedance. This can only be achieved with the help of ferrite - and even then, only with the right ferrite core and the right kind of winding. Air-cored chokes are shown to be relatively ineffective, narrowband devices... and then there's worse. Steve has also shown that the series reactances of the feedline and the wrong kind of air-cored choke can sometimes cancel, leading to a higher level of common mode current than before. This cannot happen with a ferrite choke that is predominantly resistive. For further information read Steve's page followed perhaps by my own article, at: <http://www.ifwtech.co.uk/g3sek/in-prac/index.htm#1005> That in turn will lead you on to K9YC's much longer papers. Steve, Jim and I have different styles of presentation but we're absolutely agreed on the one key point: an air-core choke and a ferrite-core choke are very different indeed. -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
