Again, remember, we are "amateurs". We do not run a metrology lab (well,
maybe one or two of us might?). 50.86-ohms DC resistance is plenty good
enough.
And consider the accuracy of the DMM with which you measured that 50-ohm
calibration source at 50.86-ohms. For example, I have three DMMs handy on
my electronic workbench. I measured one of my HP 909C type-N calibration
standards with each of those three DMMs. Here are the results:
1) 50.279 Ohms (an HP benchtop DMM)
2) 50.1 Ohms (an older Sperry DMM)
3) 50.2 Ohms (a "cheap" Harbor Freight DMM)
The number of significant digits directly reflects what is displayed by
each of the DMMs. Which is correct? I SERIOUSLY doubt the differences
would be of ANY significance in amateur radio work!
Dave - W?LEV
On Sat, Jan 25, 2025 at 4:59?PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:
The ability to enter the value of the load resistance is only used to
increase the accuracy of calibration. Small deviations from 50 ohms can
then be compensated for. The cal load supplied with my NanoVNA measured
50.86 ohms at DC so I used that as my entry.
I find this feature gives me more accurate impedance measurements but it
does not significantly affect SWR.
--
*Dave - W?LEV*
--
Dave - W?LEV
