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From: bbx!bbx.basis.com!russ@unmvax.cs.unm.edu (Russ Kepler)
Newsgroups: comp.dcom.telecom
Subject: Re: Cellular/Cordless Phones in Computer Room
Message-ID: <10196@accuvax.nwu.edu>
Date: 27 Jul 90 20:05:45 GMT
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X-Telecom-Digest: Volume 10, Issue 523, Message 4 of 10


In article <10150@accuvax.nwu.edu> julian@bongo.uucp (Julian Macassey)
writes:

>In article <10066@accuvax.nwu.edu>, alans@hp-ptp.hp.com

>(Alan_Sanderson) writes:
>[regarding 'good' class A and 'bad' class B]

>	The reason for the above anomaly is that the model that passes
>the FCC class B test is often not the model that goes into production.
>All the capacitors, lumps of ferrite, bits of finger-stock etc that
>were used to reduce emissions and meet compliance, often fail to enter
>the production bill of material. Only a cynic would say this was
>callous cost cutting. The other thing is that peripherals are usually
>tested in an old IBM PC, well shielded and running with a nice slow
>clock. That peripheral then is sold to put in high speed poorly
>shielded clones.

This isn't always the case.  In the one certification I worked on
there was an intense effort to add extra shielding to the serial and
parallel cables.  In addition the cables were cut to the exact length
to reduce the peak power radiated in those frequencies where we were
radiating the most.

Changing the cables or using cables with poor shielding would have
removed the B compliance.

But the real killer in a PC chassis is the single point ground on a
lot of the cards in the cage.  I've always wondered if you could DX on
CW with the power switch on a PC...


Russ Kepler -  Basis Int'l     SNAIL:  5901 Jefferson NE, Albuquerque, NM 87109
UUCP: bbx.basis.com!russ                                    PHONE: 505-345-5232