News flash for ya's there exists a radar that has been in use here in Oz for decades that has no problems at all seeing these guys. It's the keystone in our air defence network and it works it's magic by looking DOWN on the target as opposed to looking AT it. There is a much greater radar cross section in the plan view no matter how you try to mask it. Also stealth is really not going to do much for you, as another poster has pointed out in another thread, who cares if you've got the cross section of a bumblebee, if you're a bumblebee doing Mach 2 you're going to get shot at! 
Its not that simple. First off while JORN is an impressive systems its had its share of problems, besides, it is an American company that's a major partner in it anyways.
Secondly the use of lower frequencies for radars is no secret. The problem with it is its entirely dependant on the state of the Ionosphere to get the secondary bounce back it would need in order to detect a stealth aircraft. In much the same way your Dads Ham radio would go inop during morning or sunset hours. And you dont think USAF doesnt know that? We would simply attack from the east at daybreak, and the west at sunset, and within a day or two JORN would be scrap metal.
What JORN is really useful as is in detecting ships. Ships on the water go much slower, have much larger radar returns, and for a maritime nation with such a large coastline it is cheaper to build JORN then it would be building and manning all those extra navy ships needed to secure the coast. AND the extra airforce assets. That's why the Aussies built it, in order to secure their coastline/borders. Not primarily as a defense against stealth.
It is NOT a magic bullet against stealth aircraft. It would prove useful but its entirely dependant on conditions beyond anyone's control, "Ionosphere"/"weather", and successful strikes against its 2 main processing stations would render it useless. Luckily the Aussies are great friends of the Americans because against a stealth airforce like the USN/USAF JORN would have very limited value.
