When you are doing the coax loss calculations, don't just assume a
matched load. I don't know what antennas you will have at the end of the
run, but is it possible they might have a VSWR of 1.5:1 or even 2:1 at
the band edges? That would increase the loss over the matched loss.
At some point, open-wire feed line with matching transformers at each
end becomes a viable option.
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