You wouldn't want your EMP devices to have the range to go from your position to enemy object, you would mostly be fucking all your stuff up. What you would want to do is lob an EMP device at the enemy object, and detonate it as close as possible. Not only does it minimize damage to your own equipment, you need a MUCH smaller device. And it can be done without a ton of effort with a fast explosive, a neodymium magnet, and some copper wire to blast the magnet through, potentially launched mortar style.

I think the only reason we don't see more EMP devices is because it will screw up all your communications and potentially other equipment too, and piss off every other country within 1,000 miles with all the EM noise. You can't really protect your radios equipment from EMP devices other than to coordinate taking them all down and shielding them all. It could also potentially be a prelude to nuclear EMPs and thus nuclear war but im not all that sure what a countries response would be to EMP weapons and attacks.