Jim Kelley wrote:

Cecil Moore wrote:


William F. Hagen wrote:


an antenna has an impedence at the frequency it is being used at, and an
impedance at its resonant frequency. If either of these impedences happen to be
50 ohms and the coax being used is 50 ohms, and the transceiver is working at
50 ohms, then the swr is 1:1, and the swr is on the transmission line, not on
the antenna.





One source of confusion is, on systems with both coax and ladder-line,
the SWR on the coax Vs the SWR on the ladder-line. A 12:1 SWR on 600
ohm ladder-line can result in a 50 ohm SWR of 1:1 without a tuner.
The ladder-line can be used as an impedance transformer.



That lily really didn't need the gold paint job, Cecil.

But thanks for providing a source of confusion. How could we have a
good argument without one. :-)

73, Jim AC6XG


For additional confusion, *IF* your transmission line (coax or ladder
line) is low loss,
and if your rig can load into it, SWR doesn't much matter. Reflected
power will
"bounce" off the rig and go back to the antenna. Our rigs actually
present a very
low impedance to the antenna and transmission line. This is by design;
we want all
of the RF we manufactured to go to the antenna and none wasted as heat
in the
rig. Our rigs don't really look like the Thevinian equivalent (voltage
source with
internal resistor of 50 ohms) feeding a 50 ohm load. For a fixed
voltage and fixed
internal resistance, using a 50 ohm load gets you max power *into the load*,
ignoring the wasted power in the source resistance. Your electric power
company doesn't do that, efficiency would suck. They want all the energy
used to be in paying customer's loads. They do that by keeping their source
impedance very low. Actually, our rigs have a source impedance
of only a few ohms, and are designed to pump power into a 50 ohm load.
There is a delay involved with the reflected power getting to the
antenna, but
for the narrow bandwidth signals we transmit (SSB voice or code) this is not
significant. It will matter for amateur television up on UHF, though.

You can get a lower SWR reading than what your antenna is doing if you have
lossy feedline. The lossy feedline is absorbing some of the reflected
power.
So don't be suprised at the worse SWR if you upgrade your coax. As long as
you can load up into it, it's not a real problem.

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