Re visit this topic as I am looking at plate chokes for a tube amplifier.
I used 1010 points from 100 kHz to 30 MHz. There are 3 chokes shown here. The older National R175 shown in a prior post with its problems of 2 in band resonant conditions, a 230 uH homebrew choke for 160 - to - 40 meter. Fine but horrible beyond 15 MHz and finally a fairly nice choke at 100 uH on a ceramic core complete with a 500 pF/20 kV bypass capacitor. This choke shows a single resonance but is out of band.
It appears unnecessary to provide a short across the choke to pick up these loops if a shunt S11 measurement is used. In all cases the parallel resonate point crosses the open circuit side of the chart. A short across the choke simply rotates the reflection towards the short circuit side of the chart however the series loops stay in tact.
Alan
