[Elecraft] Coax Cable Interconnections

[Dauer, Edward]

A week or two ago there was a thread here on the permissible bending radius of various types of coax, occasioned by a discussion of “ugly balun” chokes.  The problem, I gather, is that with a small radius turn the inner conductor can migrate through the dialectric.  I filed the point away but didn’t think much about it at the time since I don’t (as of this moment) use coax chokes.  But today, as I was doing some tidying up of the rat’s nest of cables behind my desk’s misleadingly neat façade, I noticed something.  The coax – RG8 – connecting the KPA500 to the KAT500 sitting atop takes a very sharp bend.  The same is true of the cable coming out of the K3, making a sharp right turn, travelling under the desk and then making another sharp turn to connect to the amp.  The same is true of the K2 and its tuner on which it is perched – a short, sharp turn.

I am going to guess that any change to the characteristic impedence, if the center conductors in the interconnects do migrate, would not itself be a problem over very short lengths.  But the possibility of a dialectric breakdown caused by a severe migration is more troubling.  So a question for those who know about such things:  In the zeal for tidyness and the shortest possible cables, is there a significant risk?  How fast does migration occur – should these sharp-U-turn interconnecting cables be replaced on some regular basis?

Ted, KN1CBR