> Unless the loss is pretty high to begin with, this
> additional loss can usually be ignored.
The additional loss can generally be ignored with low-to-moderate amounts of
matched line loss and moderate line VSWR.
To demonstrate the additional line loss effect, compare two different feed
systems that terminate into a multiband full-wave loop antenna. Some
resulting Z values may be in the K-ohm range.
The first line has a characteristic Z of 600-ohms, while the second line has
a Z of 50-ohms. Even with low-loss, 50-ohm line terminated into the high-Z
antenna, loss can be appreciable, owing to the *additional loss* from VSWR.
Just because the 50-ohm line may be "low loss" does not mean it can work
into outrageously mismatched conditions and expect that the loss from the
manufacturers chart is all there is to reckon with. I commonly hear folks
running their loops this way with an ATU in the shack and they believe that
the line loss shown from the manufacturers data is all there is when
computing total line loss. Instead, they should keep the ATU right where it
is, but change the line to an open feeder type with higher characteristic Z
to both minimize loss and reduce line VSWR, especially when the loads are
more than 1K-ohm.
Paul, W9AC
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