[RFI] Clamp-on Ferrites

[Dan K2YWE]

Big babies! I have a couple I didn't even think of in this regard. Thanks
fof the idea.

73, Dan

On Mon, Jun 27, 2022, 10:39 AM Michael Aust via RFI <rfi at contesting.com>
wrote:

> Had very good luck with FT-240-31
> Cores with multiple turns thrust them
> 73 Mike
> WB6DJI
>
>
> Sent from my iPhone
>
> > On Jun 26, 2022, at 2:26 PM, Dave (NK7Z) <dave at nk7z.net> wrote:
> >
> > 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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