there might be something to learn from the construction of one of those more industrial common mode chokes, perhaps with ferrite arrangement, construction methods or something, which is why I asked. They might show up on ebay cheap because it seems like some generic industrial dumpster crap. Sometimes the industry gets something really right and then uses really cheap parts and it can be improved, and maybe the mechanical design is good for putting different components in it. I was thinking about getting a common mode noise filter then taking it apart to see if it gives clues, maybe its some how segmented, etc, I have a feeling if someone asked that company 'hey can you extend this range' they might know exactly how to do it, and its capped off because of a specification, we know that cheap corporate will often kill anything non essential to the specification, but it might be possible to add back in. For all I know the original design could have been 50Hz to 500MHz and the boss just said 'we need to make this cheaper'.
I think getting the low frequency range with ferrite might be more difficult then the high frequency range.
I have something like this for a telephone line, its a little addon you put on it as a noise filter, inside is a rather complex network of inductors and stuff, maybe its common mode, I never exactly figured out what it is, but maybe the topology is adaptable.
the palmer design likely has something to do with DSL.
This one looks like it can do everything but the LF
https://palomar-engineers.com/ferrite-products/ferrite-beads/FT240-3I-ID=1-4-AC-DC-Coax-Noise-Filter-RFI-Range-1-300-MHz-Bulk-Pack-of-10-p90491324I know when you use multiple EMI filters they have impedance problems that degrade their performance but usually it does not cause a resonance IIRC, it just makes the proceeding one work much less, in some cases and they do not 'stack' their attenuation, but that is for CM/DM LC filters, I never thought about pure CM filters, for me the common mode behavior was always more confusing ,especially since torroidal chokes typically are atually DM/CM filters, not pure CM, but thats with wire, coax + chokes is unstudied by me.
Active is completely different, I did not see it in the original article