On Thu, Jan 28, 2021 at 09:03 AM, John Cunliffe W7ZQ wrote:
I assume you are calibrating the nano with the pigtail installed? If not, you
are comparing apples with oranges. Unless the load is a pure restive load with
no inductive or capacitive components the added length of the pigtail will
cause a change in the vswr as it acts like a transformer of the impedance and
can very well result in the different curves you are seeing. If you don't have
a way to calibrate the nano at the end of the pigtail you can add an equal
electrical length of coax cable to the rig expert setup.
Sorry but adding a short pigtail will not be an "apples to ranges" comparison. The complex impedance will change when you add a short pigtail to a long feedline but the VSWR change will be minimal. The reason is that the complex impedance change will result in a phase angle change to the reflection coefficient but the magnitude of the reflection coefficient will only be a tiny fraction smaller. You can easily verify this on a Smith chart or by adding a few feet of coax to a feedline and then measuring VSWR.
Roger Need