There are limits, of course, as your example shows. A center fed quarter
wave is a very low impedance. I'd expect the feedline loss for that G5RV
system would be less than a couple dB on 80 through 10 meters, generally
acceptable.
73,
Scott K9MA
On 1/7/2019 09:49, Wes Stewart wrote:
With all due respect, you don't say what acceptable loss is. Of
course, you can match whatever the impedance is, most tuners will
match an open circuit because their internal losses allow it. But it
can be a fallacy that, "The line loss is so low it doesn't matter."
Absent voltage breakdown, line loss increases because of the increased
circulating current resulting from operating at elevated SWR. That
increased current is an issue in some baluns and tuners as well.
*All* of these components must be considered when evaluating an
antenna "system." Considering only one part in isolation is fraught
with danger.
Try running that 102' long "G5RV" up 50' on 160 meters. Feed it with
100' of Wireman 553 "low loss" ladderline. The 0.1 dB matched loss
turns into over 13 db at the input and that's without considering
tuner loss. (Source: EZNEC and TLDetails)
Wes N7WS
On 1/6/2019 3:15 PM, K9MA wrote:
The really attractive thing about open line, and even window line, is
that its loss is so low you can use it at a very high SWR, and take
care of the matching at the station end. This is especially useful
for multi-band antennas. The famous G5RV, for example, will work just
exactly the same fed with window line and a tuner as it will with the
usual matching section.
73,
Scott K9MA
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