No, an EMP wave CANNOT extend very far beyond its energy source. ANY EMP strong enough to cause electronics to fry, and put those who can't function without them back in the 19th century, will also bring with it fatal amounts of radiation at the very least, And because a nuclear blast isn't perfectly flat and predictable so that an EMP wave on the very leading edge of the nuclear shock wave can be perfectly placed, a lot of people will be fried instantly, and death and destruction will taper off as distance from the blast center increases. And again, A nuclear blast that is too far from earth where it doesn't cause any damage from heat and radiation, also won't cause an emp wave that can do any serious damage to power grids and electronics, because, again, an EMP wave cannot extend very far from what is creating it.
It does NOT travel like a microwave.
From the report to congress: "The HEMP effect can span thousands of miles, depending on the altitude and the design and power of the nuclear burst (a single device detonated at an appropriate altitude over Kansas reportedly could affect all of the continental United States...
The Federation of American Scientists, “Nuclear Weapons EMP Effects,” [http://www.fas.org/nuke/intro/nuke/emp.htm].
You are confusing SGEMP (Source Generated EMP) which is a very localized phenomena associated with an low altitude atmospheric burst and HEMP (High Altitude EMP) which can and does effect large areas as observed in the 50's and early 60's. SGEMP as a means of test detection at ground level was also tested in this time frame and was found that it drops off too fast.
And yes, I have worked on nuclear tests (all underground) and with folks who were involved with atmospheric testing.