Tom,
The portion of your comment that I left in below needs some additional
remarks. There was some particle of fact in what the person talked about
at the session you attended.
First, EMP remains an active concern in the design of military and
emergency communication systems, especially those operating in the HF
spectrum. Thus, there are test facilities that specialize in EMP testing
of such systems. The test consists of discharging large capacitor banks
into a tank circuit that is connected to large arrays of wires, under
which the system to be tested is located. However, no explosive charges
are used to generate the energy for the pulse.
Next, it has been generally agreed by the high energy community that the
continental 48 could be blanketed by a very large, but brief,
electromagnetic field if a single thermonuclear device were to be
detonated at a given altitude over the center of the country. The purpose
of this field would be solely to destroy electronic systems and disrupt
communications. Most of the energy would be in the MF and HF spectrum, so
systems with large antennas or long connecting leads could be damaged. (As
a side note, equipment using vacuum tubes is more likely to survive than
solid state gear.)
Finally, the mechanism described by the speaker Tom heard is not
far-fetched; in fact, that is EXACTLY the approach used by the Russians
in some of their non-contact electromagnetic missiles. (I was in
attendance at a high energy weapons conference several years ago in
Albuquerque, NM. Attendees included several US and Russian experts in the
field. During the conference, the Russian delegation astounded everyone
by making a presentation of just how they were able to generate several
GIGAWATTS of 94 GHz RF on a missile. In short: a battery supplies a
small DC current through an inductor [which is physically long] that has a
capacitor at the far end. Also attached to that far end is a gyrotron,
mounted in the missile nosecone, at the focal point of a dish antenna.
When the missile is at some predetermined range from the target, a
chemical charge is ignited, the resulting pressure wave pushes a piston
that collapses the long inductor very quickly, and the resulting dV/dT
[big step function] charges the cap with a LOT of energy, allowing the
gyrotron to deliver gigawatts of power before the whole thing flies apart
from the blast.)
So, as is often the case, there was some truth to what was said. I
suppose that if this person were to connect a "fast collapsing" coil to a
cap and some sort of antenna, there would be a pulse radiated. The range
of interference would certainly be a function of the power created and the
antenna system, among others. I think that "wiping out all communications
for miles" is probably stretching the point a bit, but real nuke blasts
will cover a lot more than "miles".
Doc asked a good question. In general, if you are protected for
lightning, you will be OK for EMP, but be advised that EMP has a faster
rise time than lightning. Modern solid state equipment is typically
small, so as long as there are no unprotected long leads connected to a
given device, it will not be affected by the EMP field. One expert on EMP
and related issues is ARRL Roanoak Division Director, Dennis Bodson,
W4PWF. Way back in the 80's, Dennis was employed in one of the Government
agencies, where he wrote a multi-volume reference on EMP and system
deisgns for protection. My employer at that time had an interest in those
issues from a marketing viewpoint, so I obtained the full set of manuals
written by Dennis and his staff. Those books served as my introduction to
EMP.
73, Dale
WA9ENA
"Tom Rauch" <w8ji@contesting.com>
Sent by: rfi-bounces@contesting.com
09/27/2007 06:07 AM
Please respond to
Tom Rauch <w8ji@contesting.com>
To
<doc@kd4e.com>, "RFI List" <rfi@contesting.com>
cc
Subject
Re: [RFI] Meter Sensitivity to Surges
I saw a presentation on EMP at the Public Service Training
Center by some Quack here in Georgia and it was laughable.
He talked about charging a capacitor up and using a small
explosive device to collapse a coil while the capacitor was
connected to the coil to generate an EMP that would "wipe
out all communications for miles". They actually paid him to
spew that drivel.
73 Tom
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