On 2/5/2023 7:57 PM, Lux, Jim wrote:
One of the nice things with the VNA is that you can do a calibration at
the end of the coax, so you don't have to figure out what the coax is
doing to the feedpoint impedance. I mean, you also need to measure at
the source end of the coax, because that's what keeps the amplifier
happy, but when trying to figure out what's going on, the VNA provides a
lot more information.
DG8SAQ's software for the VNWA he designed 10-15 years ago includes the
capability to subtract out a feedline whose electrical length is known.
I've often used AE6TY to subtract out the length of a feedline without
knowing its exact length, simply be exporting the data to SimSmith,
adding a negative length of line, making an educated guess as to its
length, and tweaking the length until I see the resonance.
You've got to do this anyway, even having good TDR data, given that VF
varies with frequency.
73, Jim K9YC
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