I am not affiliated with them, other than a very satisfied customer. There is a limited free trial you can access, but to get the full courses requires a paid subscription, valid for two years. If you don't pass, they refund your money.
Now, you don't *have* to use a study site like that, but the way they present it, it keeps track of your weak areas and reinforces it until you get it. It's not just running through the test questions either, they mix in the content, theory, math and additional links you can follow to delve as deep as you like into the subjects. I actually enjoyed the study, That stuff fascinates me (the sorcery and witchcraft of invisible radio waves).
Sounds like what I need. Thanks for the tip!