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@contesting.com> On Behalf Of K9MA
Sent: Monday, October 5, 2020 2:52 PM
To: rfi@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@sdellington.us
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