I have yet to do a teardown of a RF Explorer sig gen but looking at the specs, I highly doubt you will find an Analog ADF chip there!
It's much more likely to be a Maxim 2870 (or 2871) which seems to match the numbers dead on!
Not that it makes a big difference they both do offer good performance on lower frequencies but pretty poor above 1 GHZ, and the square-ish wave output.
Still, nice implementation and I can see with some simple add-ons this may be a useful little gadget!