[TowerTalk] Ladderline - what are the facts??/

[Jim Brown]

On Wed, 6 May 2009 12:35:08 -0400, Dan Zimmerman N3OX wrote:

>I've got a book on transformers here that puts it well when talking about
>magnetic circuits: If you ask how good air is as an "insulator" for magnetic
>flux as it covers a "wire" of magnetic material, and you draw an analogy to
>electrical wire, it's kind of like using salt water as wire insulation.

Unfortunately, that's taking the macro view when what's happening is micro. AND, 
losses are sufficient that the magnetic circuit isn't very close to ideal. The 
model is better at low frequencies where losses are much smaller. 

>But we don't have to hash this out theoretically.  All we have to do is
>build one of K9YC's recommended chokes with hefty teflon twisted pair
>instead of coax and measure the loss.  The form of the common mode conductor
>won't be so different.  If anything, common mode turn to turn capacitance
>should be less.  So choking impedance should be similar.  The only
>difference is that the differential mode vs. common mode seperation isn't
>enforced by skin effect of a shield.

>Then we just run a few kW through it and see if the core heats up, and we
>measure how much power comes out the other end.

Yes, this is a meaningful test that can be run rather easily. N6RK has suggested 
that in addition to the choke under test, a coaxial choke wound according to my 
guidelines should be added to the line to insure that the common mode 
voltage/current is small. That makes sense to me. Indeed, if it is done, you 
don't need a dummy load, you can do this with any reasonable antenna.

73,

Jim K9YC
73,

Jim K9YC