RE: Radio question
I use both the 603FF and 603FS receivers in my boats. Honestly I have not detected any difference in performance. The 603FS has a second internal antenna where the 603FF only has the single external antenna. In either my gas or fast electric boats both perform identically. Once installed I cannot even recall which is in what.
Having said that, for 10 bucks why not add the second antenna. While it may not be necessary, it can't hurt either!!