power cords with active shielding

Guys, thank you for your feedback!

@kijanki 

My power cords appear to be picking up cellular activity in the 700-900MHz range.  So you say twisting them will help reduce the cellular signal I seem to be picking up?

@blindjim

I inserted an isolation transformer (Furman P-2400 IT) into my system, so everything plugs into the isolation transformer. This had no impact on the specific noise I am targeting, but it did have a big positive affect in sound quality - removed any noise I was hearing in the music, and effectively lowering the noise floor quite a bit. But it had no affect on my intermittent noise. I called Furman directly and spoke to one of their reps and he was shocked to hear the Furman had no affect on the noise problem I am experiencing, he then said it was air born, not in the power line. Which I agree with him.

So I powered down my entire system (and apartment) for that matter and left the dedicated circuit on for my system. I put an RCA shorting plug on 1 amplifier’s input, I put a basic power cord on the amp and turned the amp on. I was able to affect the noise when I lifted the power cord and moved it around and it behaved like an antenna. So I am thinking of trying a new power cord to see if that will improve/change the situation.

I was able to identify the 700-900MHz frequency range by using this device:
https://www.amazon.com/gp/product/B007L09DLY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
It will play the frequencies it’s detecting through the speaker, and I was able to correlate the intermittent noise to the 700-900MHz frequency range which is a dedicated cellular band for emergency first responders. So that made more sense, because when I hear sirens or the subway below, I usually hear the noise.

What are your thoughts?

@kijanki 

Thank you for that clarification.  I too got a Furman device, I got the isolation transformer, the P-2400 IT.  It basically removed the noise floor from the music in my system.  I am still getting the intermittent GSM signal in my system, that is why I am exploring power cables with better shielding.

@jea48 

Not yet on wrapping the speaker cable.  I need to get more aluminum foil, then I will try that. 👍🏻🤓

@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?