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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