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Re: [RFI] EMI & EMC Conducted Noise Meaning?

To: rfi@contesting.com
Subject: Re: [RFI] EMI & EMC Conducted Noise Meaning?
From: "Cortland Richmond" <ka5s@earthlink.net>
Reply-to: ka5s@earthlink.net
Date: Fri, 6 Jan 2006 18:34:57 -0800
List-post: <mailto:rfi@contesting.com>

I erred in saying there was a 10 dB difference between Class A and Class B.
10 dB difference is for radiated emissions;  for conducted, it's worse. 
Limits are specified for particular bandwidths and quasi-peak detectors,
and a line impedance stabilization network -- a decoupling network -- of a
certain defined inductance and impedance What counts here are the relative
levels allowed.  
0.15 -0.5 MHz  Class B: 66 to 56* dBuV   Class A: 79   difference: 13 - 23

0.5 - 5 MHz      Class B: 56 dBuV              Class A: 73  difference: 17

5 - 30 MHz       Class B: 60 dBuV              Class A: 73  difference: 13

*decreases with log of the frequency

I doubt the power supply you are talking about can be as quiet as you want
it to be.  For one thing it really is an "industrial" supply. No one is
ever likely to be listening to a Braves game on the AM radio next to one, 
you know? So they don't have to design it so anyone can.  And it's a high
powered supply, too, which implies minimal impedance (RF filtering) on its
supply and output sides.

Per your separate E-mail I see you want to run laptop computers off quiet
PS's.   I am looking myself at modifying an analog 13.8V PS to 16V for a
laptop computer, to get rid of the noise a switcher makes.  It's no big
deal (assuming the caps can handle 16 volts) to move a 13.8V PS up to 16
volts. or to add a separate 16 volt regulator (if there's enough voltage
for it).   19 volts is a bit different story and you might may have to
build an analog PS or start with a 24V (analog!) one just for that. 
Switchers *can* be quiet,, but in general, for Amateur Radio use,  if you
do get a switching PS -- they're light, small and efficient -- you'll want
one that has been >tested< as quiet. And not just Class B quiet, either,
but quiet in actual use.  


> [Original Message]
> From: kd4e <kd4e@verizon.net>
> To: <rfi@contesting.com>
> Date: 1/6/2006 4:29:50 PM
> Subject: Re: [RFI] EMI & EMC Conducted Noise Meaning?
> Looked at both sites (I am an aggressive Google user)
> and as is often the case the answer is buried out
> there and I may spend hours looking and still not
> find the technically relevant answer I seek.
> Those are good sites worth saving but do not really
> answer the question I intended to ask, or at least
> I did not recognize the answer there!  ;-)
> Allow me to rephrase more precisely:
> What does that specific phrase mean to a consumer for
> AM-BC, FM-BC and TV reception and what does it mean to
> a SWL, and what does it mean to a Ham using HF, VHF,
> and UHF, please?
> The implication is that it meets the minimal business
> threshold for freedom from interference 130KHz - 30MHz
> but how to extrapolate that to real-world Ham experiences
> is rarely a matter of specs but more a matter of reports.
> I sometimes like weak signal work and adding RFI merely
> because I failed to ask the right questions is bad.

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