I also decoded F5WK a few days before, in Central TX, a bit further than IL. I'm using a 20ft active antenna (E-probe), several hundred ft from the house. Nothing special. I have a fairly quiet location in a semi-rural area. wsprnet.org will sort according to distance or timestamp so you can see the best dx for a certain call. VK4YB has some of the longest, decoded all over NA.