I concur that in some situations both a normal-mode filter (e.g. Corcom) and a
common-mode choke are required. Mitigating a big Tripp-Lite UPS was like that.
I carefully tested each approach and it was abundantly clear that both were
required.
For best results, the Corcom filter should be bonded directly to the chassis of
the offending equipment. That may mean cutting the cord very short, which we
did on the UPS. Then the CM choke is placed on the cord right nearby. If these
filters were in a nice external box with connectors on it, the long untreated
power cord might still be enough of an antenna to radiate plenty of RFI.
Gary Johnson NA6O
gwj@wb9jps.com
> Date: Wed, 29 Sep 2021 16:32:22 -0400
> From: Don Kirk <wd8dsb@gmail.com>
> Hi Jim,
>
> Once again the toroid core choke did not eliminate the RFI on its own. We
> tried the K9YC toroid choke by itself and it did not eliminate the RFI, we
> tried the corcom filter by itself and it did not eliminate the RFI. It was
> only when we used both filters in series that Mike reported the RFI was
> gone. I also tried the toroid choke before and then after the corcom
> filter with identical results on Mike?s RFI.
>
> This is not the first time that I have had to use both filters to eliminate
> RFI. The first time was on my wife?s treadmill. It really is an
> interesting phenomena. I suspect we would notice some components of the
> RFI disappear if looking at it with my SDR receiver or spectrum analyzer
> when using each filter on its own, but the bottom line is that both filters
> were required for Mike ti noice the RFI disappear.
>
> Just FYI,
>
> Don wd8dsb
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