Cecil, W5DXP wrote:
"But frequency hopping is only one form of spread spectrum."

Yes. No more than two frequencies are required to switch between, though
the transition produces more frequencies than the originals. Carson`s
rule is a close approximation of the required bandwidth and is used by
the FCC to determine bandwidth:
BW= 2(Peak Deviation + Highest Mod. Freq.)

FSK or frequency shift keying uses only two frequencies to represent
ones and zeros. Switching produces FM and is a form of spread spectrum
transmission defined as:
A communications technique in which many different waveforms are
transmitted in a wide band. Power is spread thinly over the band so
narrow-band radios can operate within the wide band without
interference. FSK is often done within the audio frequency band with no
radio necessarily used in transmission.

Best regards, Richard Harrison, KB5WZI