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Re: No UPS's - Re: [linrad] Buying the Linux PC for Linrad use.
Most of my experience is with the medical electronics end of compliance
and not with FCC compliance. I became interested in FCC compliance
because they are in some ways tougher standards to meet in terms of
radiated emissions. Medical Electronics standards are requiring radiated
emissions testing only to 1 Ghz - where as FCC requires testing 5 times
the maximum clock frequency in the PC.
Medical Electronics standards these days are being driven by the Europeans
and not by the FCC or FDA, this is good for the patient, consumers and us
hams. (The FCC does not require any susceptibility testing for electronic
devices. The Europeans require many different kinds of susceptibility testing
to be performed for sale in the EU. It's a good thing for US consumers that
multinational companies are selling these same items in the US.
For items being sold in the US, (say personal computer) manufacturer's
must meet FCC requirements for radiated emissions. Personal Computer is
considered a unintentional radiator and radiated emissions must be tested
to 5th harmonic of the MAX frequency in the PC. Most CPU's are using
multiplied clocks inside - that is the MAX frequency testing is based off!
In other words, a 2 Ghz P4 motherboard would have to be tested to 5th
harmonic of 2 Ghz... Damn this is sounding like work & I am supposed
to be on vacation!!!
Specific FCC testing for PC's can be found in the Part 15 document,
Section 15.32 (page 19) - the PDF is available as this weblink.
You want to buy a PC that has been tested to and not assembled from
tested components - see this link for the required labeling.
73's de wb9own
"B. Aurand" wrote:
> Dave, you seem to have good working knowledge of the different FCC
> certifications when it comes to computer, etc. Maybe you could give the
> group a very brief run-down of the standards and how they affect us.
> Someone else on the list mentioned only using dc-dc supplies as a strategy
> to avoid generating RFI. I don't understand this idea. Isn't a dc-dc
> supply simply a switcher? Seems to me the operation is not much different
> from the line operated computer supply. A poorly designed switching power
> supply generates RF noise and it doesn't matter where the primary power
> source comes from--line operated or battery.
> At 04:15 PM 7/5/03 -0500, you wrote:
> >I want to offer the group a piece of advice when considering
> >putting an Pc system together or adding to - that is a UPS.
> >During the certification (of our rolling around the hospital
> >product) I ruefully discovered that the PC's built in UPS
> >supply was extremely noisy - conducted emissions wise.
> >Finding this surprise required additional testing and defining
> >a new device operation mode: "power off - ATX supply
> >in standby."
> >The UPS part of the PC supply actually runs all of the time,
> >in effect it's a power conditioner which runs 100% of the time.
> >Note, if you are considering an external UPS supply - they
> >may also operate all of the time as "power conditioners."
> >The switching power supplies in these things are very noisy!
> >The manufacture of these devices are claiming compliance
> >(to the FCC's old definition of a Class A digital device for
> >radiated emissions,) that the "USER must accept interference
> >from the operation of it." (This is my pharaphasing of the FCC
> >If you want to buy a UPS - ask for a "money back guarantee"
> >given the possible of radiated emission interference. Some
> >manufacturers are stating their UPS's are Class B compliant,
> >try them first - but make sure there exists a money back guarantee
> >in case it "self jams you." Good luck & 73's
> >dave garnier - wb9own