Had that happen to me once. Didn't want to force it and simply went on top and squirted some silicone, (not wd wo) down in there. Although WD40 would work, just not a fan. Might have someone on roof to help the antenna and by helping I mean just get it started while other person cranks.
Thanks to all who replied. Antenna was a bit out of alignment. Also took time to lubricate the unit as suggested. This Forum is a real source of helpful information and friendly RV enthusiasts . This saved me a repair bill!!