Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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I measured RF noises on the power lines. (long)

Posted by cheap-Jack (M) on April 24, 2006 at 08:58:10

In Reply to: Re: Really? posted by J.Rankin on April 23, 2006 at 09:37:27:

Hi.

Yes, RF power lines noises are always there, period. For sure these
noises come inward from our mains line as I mesured them, from time to time.

I use a brandname wideband powerline & EMI noise analyser & measured
wall outlets just immediately next to my audio/video gears, my friends' home & for control, I also measured at an electronic store many blocks away from my home.

Power line noise level ranging from 103-105mW (on 115-102VAC 60Hz)in my & my friends from a few blocks apart, but powered from two different hydro utilities. 138mV measured from an AC outlet which powered quite a few DVD players (all switched on) on display in that electronic store. One thing really worries me is I heard radio broadcast coming from the power lines of my & my friends homes, from the speaker on the noise analyser.

In the retail store where I tested, no radio broadcast was heard & the EMI noise level is very low: from zero to 0.3mV although its power line noise is up to 138mV.

This showed that digital equipment, e.g. DVD players, do emitted REI noises into the power lines whenever they are swithced on.

With this meassurement, it confirms to me that we need:

(1) effective AC power line filteres immediately right at the power points for our audio/video gears.
(2) discrete power lines for both analogue & digital equipment.
Don't plug your CD player into the same power outlet with your
amps & record player.

To resolve such problems, I've hard wired discrete power lines direct from my houehold fuse panel exclusively for my audio gears
with my DIY AC line filters exclusively for my anlague & digital gears.

With digital gadgets all over the place even in our home, e.g. cordless phone (up to 5GHz), cell phones, wirelss routers, switching power packs for PC notebooks, camcorders, LCD monitors & platpanel TVS, our audio gears are subject to all these RFI invasion let alone SS rectifier switching noises from our audio amps which to me is chicken feed.

The CE industries seem to perceive such problems, I can see many brandname audio, video & digital equipment supplied with power cords, CATV cords, speaker cords (for LCD & plasma TVs) clamped on EMI/RFI ferrite shield rings. Also, some hi-end brandname audio interconnects also clamped on such RFI ferrite rings.

I just finished building a 6V 5AH battery power supply for my phonostage tube heaters, using a 110v/220V - 12V7.2A switching power module to recharge the battery. It also prompted me to add a large EMI/RFI ferrite ring to the DC power supply cord from the rechargeable battery supply to my phonostage. Better play RFI safe!

c-J

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