To avoid mod killage, everything I say here is completely legal (as in, why I'm leaving out direct specs)
Two ways to create an EMP weapon.
Herf gun/EMP bomb.
Herf guns are simple, and anyone with some Electromagnetism and circuitry knowledge and an old microwave can build one. However, chances are you'll fry your skin and go blind. I'd avoid it. What it does, it uses the magnetron (sp?) from the machine to generate a directed stream of microwaves that overload circuitry. Not truly an EMP weapon, but functions similarly. (also, arcs metal,which is neat)
EMP bomb. The closest thing I can think to a "bomb" is something called a explosively pumped flux compression generator. For this you would need a metalshop with precision equiptment, a highly trained team, and EXTENSIVE professional knowledge in circuitry and electromagnetism. How it works, in short, is uses an explosion to compress a solenoid around a directional EMF field, utilizing Maxwell's modified Gaussian formula for magnetism. flux=integral(BxdS) Flux is conserved despite a massively decreasing dS, causing magnetic fields to arise in the range of thousands of teslas, which due to various other formuli relating current vs conflicting variable magnetic fields ect cause MASSIVE surges in circuitry, blowing it out.
(Also, EMP waves from Extremely high powered explosions, especially seen in high altitude Nuclear explosions, but that's a lesson in atmospheric reflection amplification and all sorts of other fun weapon physics)
Hope you enjoyed my fun little deviation in applied physics.
