Topband: Thanks!

[Jim Brown]

On 5/18/2013 10:35 AM, Charlie Cunningham wrote:
>   If you get the larger beads/tubes thatwill fit over RG-213 etc. you can make excellent 1:1 current baluns by slipping them over the cable before putting the connector on.

These are not "excellent" 1:1 current baluns below about 75 MHz. Below 
that range, they are a lousy common mode choke, because they are 
inductive. Inductive chokes resonate with a line that is capacitive, so 
they actually increase the current. A line shorter than a quarter wave 
is capacitive; so is a line between a half wave and 3/4 wave. And so on. 
That's why we want a choke that is highly resistive -- the resistive 
component always reduces common mode current, which is the objective of 
a common mode choke (the so-called "current balun.")

There's an extensive discussion of this in my RFI tutorial, and also in 
the Coax Chokes power point (which is a pdf).  On my website. 
k9yc.com/publish.htm

73, Jim K9YC