[RFI] Noisy PC Speakers

[Hare, Ed W1RFI]

Well, I could have used the common-mode filter, which we'd do to solve an RFI issue, but it really was interesting to see the conducted noise increase due to the addition of length to the speaker wires.  I would expect an increase in radiated noise, but was pretty surprised at the change in conducted noise.

I was able to do the same thing by adding that counterpoise to the case of a power supply.  This suggests that grounding a power supply with a wire of finite length could actually increase its noise.

This should be put out into the standards community, and I am pretty well positioned to be able to do that.

Ed, W1RFI



-----Original Message-----
From: RFI <rfi-bounces+w1rfi=arrl.org at contesting.com> On Behalf Of K9MA
Sent: Monday, October 5, 2020 2:52 PM
To: rfi at contesting.com
Subject: Re: [RFI] Noisy PC Speakers

Perhaps because the speaker wires were acting as a counterpoise, and actually increasing the conducted emissions on the power leads. Did you try a common mode filter on the power leads when the speaker leads were connected?

73,
Scott K9MA

On 10/5/2020 1:00 PM, Hare, Ed W1RFI wrote:
> < Second, every wire/cable connected to a noise source (in this case, 
> the Class D amplifier, but also including switch-mode power supplies) 
> forms a transmitting antenna for common mode current on those wires. 
> So nothing in your lab tests is surprising.>
>
> Actually, it is very surprising, at least to me, because when we changed the nature of the speaker loads, the conducted emissions on the AC mains increased.


--
Scott  K9MA

k9ma at sdellington.us

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