On Jun 12, 5:43*pm, Owen Duffy wrote:
wrote :

...

Even with a 80/1 mismatch, ladder line has low loss.

30m of Wireman 551 with a load of 5+j0 has VSWR=80 at the load end, VSWR=28 *
at the source end, and the transmission loss is 4.6dB... 65% of the input
power is converted to heat.

Speaks to your meaning of "low loss".

Mythical properties are ascribed to ladder line, some of attributable to
ARRL publications.

Owen

I might have been a bit carried away with the degree of mismatch
and loss, but I still think running the ladder/window line the whole
way to the tuner will still be the best in most cases for "all band"
use.
If the major portion of the feed line will still be ladder line, even
with
the coax lead in, he will still deal with the same line losses for the
majority of the run with such a severe mismatch.
It won't be that bad most of the time.
With the coax and choke addition, even more loss is added to the
system. And if he saw an 80:1 mismatch, just 15 feet of RG-8
should cost you half your power at 14 mhz. That's more loss than 15
extra feet of the ladder line which at 80:1, should be about 1 db loss
or so.
I just find the addition of the coax and choke as totally unnecessary
unless there is no way at all to feed the ladder/window line through
to the shack.
Sure, there are losses with the balun used in most tuners, but I
consider that a price to pay for a multi band antenna.
Myself, I don't use many all band antennas..
Most of my dipoles are single band, and coax fed. :/
Here is one online calculator which seems to match your
numbers fairly close if set for 14 mhz. They include the
551 line as one of the choices.
I notice "generic" 450 line has less loss.. I don't know
what the difference is between generic and 551..
Maybe 551 has more plastic, and less open window..
I notice generic 600 ohm ladder line will show about 2.2 db
loss with an 80:1 mismatch. I'll agree.. Maybe not low loss,
but it's quite usable considering an ugly 80:1 mismatch.


http://www.qsl.net/co8tw/Coax%20Calculator.htm