>> A RLC group is a resonator and will have a peak frequency at which its
>> impedance will be maximum (!).
>
> Surely you mean minimum? Using low ESR caps could increase emissions by
> reducing the rectifier diode reverse current, and thus the high
> frequency currents in the primary side switching device.

The emissions from any ringing in the coil, rectifier and filter cap at or
after switch switchoff is what I have in mind. A cap will have a series
and a parallel resonant frequency. The annoying one is the parallel. This
is especially well peaked in low esr caps. I found that I needed an extra
choke and cap (or symmetric pi filter) to remove it.

There was a scheme for an AM radio once upon a time that used (new,
perfectly good) electrolytic caps as coils. It was in Radio Electronics or
such a long time ago. I saw a reprint once.

Peter

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