Doug,
The answer may be here in K9YCs article
http://audiosystemsgroup.com/Pin_1_Revisited.pdf
Let us know if you are successful resolving teh matter and how
you de RFI'd teh system
73, Dennis N6KI
Sandy Eggo
On Mon, Oct 20, 2008 at 12:35 PM, Doug Grant <dougk1dg@gmail.com> wrote:
> My wife recently bought a new PC. The (conventional analog) speakers
> that came with it were defective, and when we returned them, the shop
> was out of stock, but offered to give us a pair of HP-branded
> USB-powered speakers at no charge.
>
> They work fine.
>
> However, they also appear to be the source of some really ugly RFI
> that I hear on 160 and 80M. Even with the PC powered off, it appears
> that the USB port still delivers power. With the PC off, and the
> switch on the speakers turned OFF, there's no noise. If I turn the
> power switch on the speakers ON, a broad 20-kHz-wide (+/-) signal
> appears, spaced every 150 kHz or so, and drifiting around slowly. A
> quick test of a clamp-on ferrite on the USB cable, then wrapping 10 or
> so turns of the cable around a bigger toroid did not make a dent in
> it.
>
> Not sure if it is noise on the USB power or if the speakers have
> poorly-decoupled Class-D amplifiers in them causing the noise.
>
> I am sharing this so that anyone with a similar noise problem might
> benefit, and also to see if anyone has encountered this problem, and
> has a better solution than mine (which is to ask my wife nicely to
> turn off the PC speakers when I am on the low bands).
>
> Does anyone make a USB filter that cleans up the power line without
> compromising the data lines?
>
> 73,
>
> Doug K1DG
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