Here is a display for S11 from the vna. Sweep is 1 - 30 MHz, 512 points. A simple SOL cal and then a set of clip leads to the choke.
Choke is standing up right on the tube chassis and the rack panel in place. All is good pass 20 meters... Then things get interesting
as you approach 16 MHz and 21 MHz. Be careful there! A simple mod to the R-175 choke spread the top section of windings
out and moved the self capacitance created so that the resonance that exited was well removed from the HF band. On the
vna easy to see. Not so easy using the GDO. Can be done, just takes time and patience!
Please note. At low frequency as expected the shunt measure of the choke starts at the short side of the chart and rotates CW.
Eventually, parallel resonance occurs. Increase frequency some more and there is where the FUN begins.
