[TowerTalk] choke / balun design needed

[Jim Brown]

On Mon,4/27/2015 11:33 AM, TexasRF--- via TowerTalk wrote:
> Thanks  for the information Jim. It all makes good sense down to the part
> about  differential loss. That is a new term for me so I did a Google search
> for  "coaxial cable differential loss" to see what it means.
> Guess what: there was nothing shown for that subject. Wonder just what it
> is about?

Thanks for the question, Gerald.

By "differential" I mean the loss INSIDE the line due to it carrying 
power. We use the words differential mode for the transmission of signal 
within the line, the differential voltage is the voltage between the 
conductors, the differential current is the current inside the coax. The 
common mode current is the voltage ALONG the line. With coax, it's on 
the outside of the shield. With 2-wire line, it's split equally between 
the conductors.

The condition that Dean is talking about is a serious mismatch -- for 
example, an 80M dipole fed on 40M. In his example, there are very high 
standing waves within the coax, which produces very high losses within 
the coil of coax that forms the common mode choke, so that large coil of 
coax gets quite hot. Dean used TLW for his model of this, and I modeled 
it in SimSmith to confirm his work.

73, Jim K9YC