Hi Bob, Thanks for your comment. As I noted in our private email exchange, the Johnson Matchbox was a last-minute substitution for an Elecraft BL-2 balun that was overheating on some bands at 100 watts. I had not been using that configuration previously, but faced with the choice of going QRP or QRT in the ARRL DX CW contest at its commencement, I opted to put the Matchbox in place of the balun. I used that same configuration again for my brief foray in the ARRL DX SSB weekend, and that led to my original post here about K3 TX power foldback with only modest rises in SWR presented to the internal ATU.
For my particular antenna and feedline length, the indications are that common-mode currents are high on several bands, which is not surprising to me. The Matchbox can reduce the SWR presented to the rig on some bands, but not all of the ones I needed for good contest outcome. That motivated use of the internal ATU rather than just putting the ATU in 'BYPASS' mode and relying on the Matchbox alone. I agree that using a good, high common-mode impedance choke is preferable to the Matchbox, and the internal ATU of my K3 is quite capable of handling the native SWR presented by the antenna/feedline using the balanced-to-unbalanced transformer in its 1:1 configuration. It appears that the balun's common-mode impedance is not sufficient to reduce the common-mode currents presented by my particular antenna/feedline system. That's not the balun's fault, and one day soon I'll measure its common-mode impedance to better understand its power-handling limitations. With thanks as always for your insight and comments, 73, Mike, K8CN ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
