On Tue, 29 May 2007 20:36:17 -0400, Tom Rauch wrote:
>Not only must the PS make noise, the noise must somehow get
>into the receiving system.
I own five IBM T-series laptops (T20, T21, T22, T41), and none of
the power supplies have RFI issues. In Chicago, I used them within
a few yards of receiving antennas. Here in CA, I've got a lot more
separation to most of my antennas, but also a much lower noise
level. I DO, however, hear VHF noise (2M SSB) from mouse movements
that I blame on the video system, and is greater if the laptop is
plugged into power.
Noise sources need an antenna to radiate it. Internal wiring will
radiate if the box is poorly shielded and current loops are large
enough. A good designer will minimize those loop areas, using
circuit layout and multilayer boards to create a ground plane
(stripline or microstrip).
External wiring will radiate if the designer was careless about
allowing coupling to it. That external wiring can usually be
choked effectively with ferrites. You're usually out of luck with
the internal antennas.
One thing I'm learning is that some notebooks will run on a fairly
wide range of DC voltages. My IBM laptops all work fine on the
13.8 VDC supply that runs my radios -- I just need to be careful
not to overcharge the internal batteries, and the IBM software
allows me to monitor battery voltage and current. My wife's Dell
also seems to run OK on 13.8VDC, but doesn't provide the
monitoring software. So, if I had a notebook with a noisy P/S, I'd
spend some time monitoring power supply voltage and current, then
work up an alternative DC supply to replace it. I've done that
with these laptops to create a monster UPS that can hold them up
during a long power outage.
Jim Brown K9YC
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