[Milsurplus] EMP Specs

[Tom Dawson]

MIL-STD 464A includes a sample UNCLASS EMP pulse that is a reasonable start 
on estimating what you need to do to protect your receiver.

The plot is here:  http://www.radio-science.com/EMP/emp_pulse.jpg.  Its the 
IEC EMP test pulse.  No doubt Uncle has beefier ones but they are not 
available to me.

This is similar to the Lightning test pulse but rather faster.  Also 
Lightning is usually expressed in terms of current rather than field 
strength.

I my experience, the EMP protection is part of the facility or platform that 
the radio is installed in rather than the radio itself.

For a 40 meter halfwave dipole and a 50 ohm receiver (neglecting the 
mismatch loses) it looks like you'd get a peak of about 7800 volts across 
the receiver input.

That is a peak power of about 1.2 MW but it exists for only about 20 ns so 
that's only about .025 joules.  So if you can find a gas discharge tube that 
is fast enough, it would not need to be to big for a single EMP.

One thing for certain: a semiconductor junction or insulated gate structure 
can easily expire in the 5 ns risetime of the pulse.

73

Tom
WB3AKD