[TenTec] SWR is a DUMB Indicator of Antenna Performance

[Steve Hunt]

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
>