Someone with a Rtg. 6 directional antenna (Avail 4, 150nY, Signal Rating

and an electronic warfare skill using "jamming on the fly" (UW, p. 105) can effectively block the communications of everyone that lacks an electronic warfare test (because it cannot be defaulted). Is this really working as intended?
This makes jammers really obsolete, because you can ignore them by simply buying ECCM. Also, a jammer costst Rtg * 500 and is forbidden, a directional antenna costs nothing (Rtg*25), is completely legal and readily available.