[Amps] Input SWR revisited

[Paul Christensen]

> "Explain the case where a 100 ohm load ( 2:1 ) can be a 1:1 swr at the
transmitter with a length of 75 ohm cable.  I've changed the cable
length and improved the SWR.  Don W4DNR²

See "My Feed Line Tunes My Antenna!² by By Goodman, W1DX


In your example, let¹s assume the antenna is 100+j0 (a pure 100-ohm
resistance).  Connect a 1/4-wave section of nearly lossless 75-ohm line to
the antenna.  The SWR as measured by the rig¹s SWR meter or wattmeter at
the input end of the line will be nearly 1:1.  That is the Z(50) SWR, not
the Z(75) SWR.  The Z(75) SWR is still 1.33:1 and is set by the 100/75-ohm
mismatch at the load.  However, from this point on after the 1/4-wave
section - and all the way to the transmitter, we can add any length of
Z(50) cable and the Z(50) SWR will remain 1:1.

Paul, W9AC