I'm evaluating a low pass filter (for 6m) I acquired recently, which does a dandy job up to 250 MHz or so, but it has a few spurious responses between 300 and 500 MHz. It behaves like the 50 pF/7.5 kV and 100 pF/5 kV doorknob capacitors it uses must be self-resonant in this range. Can anyone confirm this? 73, Steve VE3SMA