I agree with those who say that the problem is getting worse even
though the standards are getting more strict.  With the fundamental
frequency of the clocks in high-performance computers and telecommunications
systems now in the 100 to 200 MHZ range, that puts them in the prime
realest ate area that most of the world uses to carry out its business.
The carriers and sideband splatter from modulation of those carriers by
switching activity makes for what has been called electronic smog.  It is
very bad on a college campus or a business building with lots of computers
and a fast network.

        The steady carriers from clock generators are a show stopper if they
land right on the frequency used by an organization to communicate, but the
worst problems are those caused by the noise bursts that happen in a
continuous torrent while hundreds of processors crunch data and chatter back
and forth over the 156-MB network backbone.

        That noise is a very wide-band crackle that sounds like a lightning
storm in fast-forward if one uses an AM receiver and hears it.  The noise
disrupts the sort of narrow-band FM receivers that are the main stay of
two-way radio systems and pagers all over.  Narrow-band FM or NBFM receivers
commonly mute the speaker between transmissions by rectifying the noise
picked off from the discriminator in the absence of signal.  A high-pass
filter gets rid of the audio so the only signal at this point is noise when
nothing is being received.  This noise is rectified and used to bias the
muting switch.  When there is extra noise from computers or other sources,
that noise fools the mute in to thinking that the signal is not there or is
weak and it kills the speaker.  The person using the system may not hear a
thing while somebody in the field is needing help.  They may also hear bits
and pieces of the transmission and waste time calling for repeats.  They
will probably not think of computers, but will call the service technicians
who will possibly miss the problem but won't miss sending a bill to the
customer.  Even if the technician suspects noise interference, he or she
may have trouble finding or curing the problem because it is coming from
several locations at once.

        This last Fall, when hundreds of students and their computers moved
in to student housing for the new school year, one of our campus public
safety radio systems got hard of hearing on the day the students moved in.
There does not appear to be any malicious behavior involved and the racket
appears to be from many sources.  The only thing that has changed is the
availability of 100 and 200 MHZ systems for the masses.

        The stories about lap-top computers on airplanes and other tails
of the strange probably do get mangled in the retelling, but the problems
are real and not to be taken lightly.

Martin McCormick WB5AGZ  Stillwater, OK 36.7N97.4W
OSU Center for Computing and Information Services Data Communications Group