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
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