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From: julian@bongo.uucp (Julian Macassey)
Newsgroups: comp.dcom.telecom
Subject: Re: Cellular/Cordless Phones in Computer Room
Message-ID: <10150@accuvax.nwu.edu>
Date: 26 Jul 90 14:47:05 GMT
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X-Telecom-Digest: Volume 10, Issue 518, Message 7 of 9


In article <10066@accuvax.nwu.edu>, alans@hp-ptp.hp.com
(Alan_Sanderson) writes:

> The computer equipment is
> FCC Class B certified for RFI emissions (computer room environment -
> not personal computer Class A).

	The above statement is logical but not right. Equipment
meeting Class A requirements are Industrial/commercial. Class B covers
domestic.  The requirements for class B are far more stringent. The
FCC recommends that all equipment should strive for Class B
compliance.  The requirements of Part 15 Subpart J have recently been
revised.

	In reality you may find Class A equipment that causes less
interference than Class B equipment. You may also find equipment that
is supposed to be Class B that causes so much interference as to be
unusable. I usually get flamed mercilessly for saying this sort of
thing. Alas, no one ever wants to pay to challenge me at a test site.

	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.

	Just as a matter of interest, I have an apartment loaded with
a PBX, several CPUs, and sundry radios (both receivers and
transmitters). My main source of interference is a light dimmer in the
apartment building next door. When are the FCC going to do something
about light dimmers?


Julian Macassey, n6are  julian@bongo.info.com  ucla-an!denwa!bongo!julian
N6ARE@K6IYK (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495