[RFI] Clamp-on Ferrites

[Dave (NK7Z)]

https://www.nk7z.net/rfi-now-house-cleaning/

Fair Rite part numbers are about 3/4 of the way down...

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 6/26/22 13:11, Dan K2YWE wrote:
> We have a TV whose audio is seemingly susceptible to HF RF in every port.
> It hums in time with ICW pulses on the HF ham bands. The picture is
> unaffected.
> Using HDMI input from wi-fi Roku device.
> 
> The hum is barely perceptible using internal speakers but loud enough to be
> obnoxious when using cheap passive earbuds on a long extension cord. It's
> still there but much less when the earbuds are plugged directly into the TV.
> Unplugging the HDMI cord at the TV end has no effect.
> Unplugging the HDMI at the Roku end makes it louder. That might rule out
> the Roku except that unplugging the Roku wall wart makes it better,
> I have only one clamp-on ferrite to experiment with and I have no idea what
> material it is. It has no when effect placed on the earbud extension cord
> except that when the clamp is almost closed (small gap in mag path) around
> the earphone cord the interference drops. Fully closed, it's back to full
> interference. It's hard to imagine I'm saturating the core, so it may be
> somehow tuning with the cord inductance.
> I want to isolate the TV as much as possible by choking all the I/O, namely
> the AC line cord (no waart), HDMI , and earphone jack. I'd prefer a snap-on
> core with a big enough hole in which to put 2 or 3 turns of the line cord
> and the earbud extension, but a smaller hole will suffice for
> experimentation and maybe using a few tandem. Freq is 2-0 MHz.
> 
> Any suggested snap-on cores or other ideas?
> Dan Z
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