Jeff wrote:
With a 50 ohm source and 200 ohm load the loss is calculated as is 3.93dB
and VSWR is 3.98:1
Changing to a 100 ohm source the loss is calculated as is 4.78dB and VSWR
is 3.41:1

Looks like your losses and VSWR are taken on the wrong
side of the source resistor.

source R
source V----x--/\/\/\/\/\/\--y----T-line---load

Loss and VSWR should be calculated at 'y', not at 'x'.
We are interested in the VSWR and losses *on the T-line*.
Please change your reference point from 'x' to 'y'.
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73, Cecil http://www.w5dxp.com