Dear Owen: Well do I remember the onset of EMC awareness that came with
the early anti-skid systems. One horror case took place in Chicago with a
bus. One of the many short bridges in Chicago has metal decking and a bus
stop at the far end of the bridge. The bridge also is aligned with the
Sears tower (in downtown Chicago it is difficult not to be aligned with some
strong RF radiator - it is worse than a carrier). Bus starts onto the
bridge. Patrons stand to get off at the next stop. Breaks fail while on
bridge. Driver fully asserts the brakes. Bus arrives at the end of the
bridge and the brakes start to work. People go flying.

I was a witness of the (very early and crude) method used to test
systems. Not anymore! Today, whole cars are zapped from all directions,
all frequencies, and at huge amplitudes. A huge effort was made to find out
what sort of signals a car might encounter. I once rode in a van all the
way to Chicago glued to a SA to record strong signals. The worst that I saw
was a VOR signal (few hundred watts at ground level with a very good radial
screen and near the road) and a CB signal. Others in the project measured
at VOA and LORAN sites. An FM broadcast antenna was found to radiate a huge
signal onto a public street - see, you know that antenna design would be
worked into the discussion - in this case an incompetent, but not unusual,
antenna design.

At work, we have a big RF amplifier used to zap devices in order to find
out where they die. Had to get a waiver from FCC because, even though the
amp requires three-phase, it could be used on 27 MHz.

Critical equipment is much more EMC capable today.

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Owen Duffy" wrote in message
...
Cecil Moore wrote in
et:

Stefan Wolfe wrote:
One thing that works real well is to transmit near the x-ray radar
band where you have privileges. The traffic may slow down a bit as
you set off the radar detectors :-)

A number of years ago (I forget exactly what year) a
ham friend of mine discovered that he could cause a
new Cadillac to stall simply by keying his transmitter
as the Cadillac was passing his camper. That design
problem was probably fixed rather quickly.

Back in the '70s I was working on a project that saw me reading papers on
the effects of EMR on various things. Amongst the papers was one dealing
with the susceptibility of the electronic anti-skid technology introduced
on heavy transport vehicles to meet (then) newer more stingent braking
distances. The braking systems were susceptible to ingress of RF,
resulting in wheel lockups. You can imagine the results of a 22 wheeler
at highway speed when a chook alongside comes up with "Breaker, Breaker,
any taker?" and locks up most of the wheels on the transport. I read
other papers on rear wheel lockups in a certain brand of passenger
vehicle due to RF induced downshift of the (electronically controlled)
automatic transmission at highway speeds.

The EMC issue seems better understood by vehicle manufacturers today,
though you still hear of RF triggered airbag deployments from time to
time.

I won't go into the papers on effects on aircraft, some of you may fly
from time to time! A paper on propagation of EM waves through rectangular
slots in thin sheet metal looks innocuous enough until you realise that
it is talking about an aircraft window (in the days when almost all
aircraft had a metal skin).

Owen