[TheNext]

Frequency hop is a natural process. Natural cannot be patented but she was given a lucky privileged monopoly.

[KarlInOhio]

Inventing something having a transmitter and receiver change carrier frequencies on a preplanned schedule isn't natural and I wouldn't say it was obvious either. The only shortcoming was trying to get both sides run synchronously - they had a tendency to get out of synch without a high precision timer or some self clocking signal.