[Amps] Length of coax from xcvr to amp affecting input swr.

[Paul Christensen]

> The addition of lossless transmission line changes the complex impedance, 
> but not the SWR.

True as long as the characteristic Z of the additional line remains 
constant.  In the literature, this footnote needs to be added to the general 
statement above.   It's been repeated over-and-over again with the 
presumption that SWR *must* be the same at any point along the entire 
distance of a transmission line, notwithstanding loss.

For example, consider a load (e.g., amp input) that is connected to a 
coaxial cable of Zo = 50, and at some random distance down the line, it is 
jointed by a line to the source with Zo=75 cable.  The SWR on each section 
of the overall line will not be the same, even if both sections are 
loss-less; SWR will be one value on the 50-ohm section, and a different 
value on the 75 ohm section.  But the SWR is not the same along the entire 
distance of a loss-less, or nearly loss-less line.  Because of this, 
reference should be made that SWR does not change along a line, provided the 
characteristic Z of the *entire line* is constant.

> 2. The meters are sensitive to the load impedance, and are not 'perfect' 
> or 'ideal' SWR meters. The internal SWR detection in HF rigs are usually 
> pretty bad in this respect. Perhaps try a Bird meter to see what is really 
> going on.

My money is on this and also pointed out by Gary, K4FMX.  It's been a while 
since I've experimented with various directional couplers as the standing 
wave builds on the line from the load, but a monimatch, for example, may 
behave differently and report a different value than a Thruline section.

Paul, W9AC