Bob,
Another typical application where this stuff matters is a multiband
doublet fed with ladderline. For convenience a lot of folk terminate
the ladderline at a balun outside the shack, and then use a short length
of coax from the balun - through the shack wall - back to the tuner. If
you want to know the real losses in that short coax run, avoid those
"added loss due to SWR" tables.
Here's a related "Ham Myth". How many times have you heard the increased
loss due to SWR explained along these lines:
"The forward wave - because it's a travelling wave - suffers the
matched-line-loss. Part of the forward wave is reflected at the load,
and that reflected travelling wave now suffers the matched-line-loss
back along the line until it reaches the source where in turn it is
partially re-reflected etc etc etc. The total loss under mismatched
conditions is then the accumulated individual losses"
As we have seen, that type of explanation is flawed - it predicts that
the total line loss will always be higher under mis-matched conditions.
It also suggests that the losses are evenly distributed along the line.
We know that isn't true - a line with a 10:1 SWR has 100 times the loss
at current maxima compared to the loss at current minima.
Steve G3TXQ
On 16/09/2014 00:09, Bob McGraw - K4TAX wrote:
Good explanation and I do see the reference. Thanks.
73
Bob, K4TAX
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