Are Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Sequence (DSSS) modulations? I am confused because I have read that these are also used e.g. with Gaussian Frequency-Shift Keying (GFSK) modulation? Can modulated signal be modulated again?

• FHSS and DSSS refer to the carrier frequency (jumping around in the spectrum) not the modulation used. – JIm Dearden Jul 12 '15 at 11:41
• @Jim Dearden What are they technically? I have seen thet they are referred to as modulations. – Quirik Jul 12 '15 at 11:45