power cords with active shielding


Has anyone tried any power cords with active shielding?  I would appreciate any comparisons or opinions towards power cords with active shielding.
128x128james1969
@kijanki 

I have a police station down the street, and a fire station down one block from me.  So the public safety GSM band would probably be in high usage during the daytime (like what I experience now).  I'm up at early hours to enjoy my system (when the city is asleep) and there are no sirens to be heard.  The subway still comes and sometimes I hear the noise, we have cell phone service now down in the subway system.

I wonder if the FCC would listen to my case?
@kijanki,

Back in the late 1980s I had the same problem with a Ham Radio Operator just a few houses away. I bought a 31" console TV that had a synthesized surround sound amplifier. When I hooked up a pair of remote rear speakers to the TV it didn’t sound all that bad. That was until the Ham operator decided to dust off his radio and start transmitting again. Every time he keyed the mic and spoke I could hear his garbled voice through not only the two rear speakers but the front speakers in the Console TV. Even with the TV turned off I could still hear the guy when he was using his radio, though not as loud when the TV was turned on. The guy’s garbled voice did not change with the sound volume setting of the TV.

Problem ended up being the two speakers cables that ran around the wall of the room to the rear speakers. The two cables were working as an antenna and picking up the Ham Operator’s transmitted signal.

I tried everything. Ferrite beads on the power ac cord. Ferrite beads on the two rear speaker cables at the two speakers. Filter caps, at the speaker terminals. A factory made 95% shielded twisted pair cable for the speaker cables. Nothing helped.

I finally disconnected the rear speaker cables from the TV. With the rear speaker cables disconnected, the front speakers in the TV worked fine. Not a hint of the Ham’s garbled voice.

In james1969 other running thread I mentioned he might try wrapping some aluminum foil around the speaker cables feeding his 2 speakers. Not sure if he tried it or not. I am not sure the aluminum foil will even help.
https://forum.audiogon.com/discussions/high-frequency-intermittent-noise

As for ferrite beads and filter caps. Don’t they have to be selected for the frequencies you are trying to block, reject?

Jim

@jea48 

Not yet on wrapping the speaker cable.  I need to get more aluminum foil, then I will try that. 👍🏻🤓
Jim, speaker cables are antennas for the electrical noise since amplifier has low output impedance only for low frequency signals.  Induced noise enters amps input thru the feedback loop.  

As for the ferrite - on one hand you need highest permeability, but on the other high frequency response.  Self Resonant Frequency (SRF) specification might be useful since above this frequency impedance of the choke for common mode signals will drop like a rock.  Read this:
https://www.coilws.com/index.php?main_page=page&id=128

I've been once in the company that had so much of the noise pollution (multiple high frequency seem welders) that nothing worked - not even telephones.  Technicians there told me that common rules, like grounding shield on one end only don't even work. At the end they had to put every power cable in conduit.  We had to put our equipment, we sold them, in the metal NEMA box with metal mesh screen on the front door glass.
@kijanki ,

Thank you for your response.

If you find the time would you please read through this thread of james1969.
https://forum.audiogon.com/discussions/high-frequency-intermittent-noise
Maybe you can think of something to try.

Jim