Subelement G: Transmitters— Topic 56: Technology
Question 3-56G4
Element 3 (GROL)What term describes a wide-bandwidth communications system in which the RF carrier varies according to some pre-determined sequence?
Explanation
Spread-spectrum communication intentionally spreads a signal's energy over a much wider bandwidth than necessary for the information content alone. This is achieved by modulating the carrier with a pseudo-random noise (PN) code (Direct Sequence Spread Spectrum - DSSS) or by rapidly changing the carrier's frequency in a pre-determined hopping pattern (Frequency Hopping Spread Spectrum - FHSS). Both methods utilize a specific, pre-determined sequence to vary the RF carrier, making the signal robust against interference and difficult to detect or jam, fulfilling the description perfectly.
AMTOR and SITOR are specific, relatively narrow-band digital communication modes, primarily for text, utilizing error correction, not wide-bandwidth spreading techniques. "Time-domain frequency modulation" is not a standard or meaningful term in radio theory; frequency modulation naturally occurs in the time domain.
Related Questions
3-56G2 How can parasitic oscillations be eliminated in a power amplifier?3-56G3 What is the name of the condition that occurs when the signals of two transmitters in close proximity mix together in one or both of their final amplifiers, and unwanted signals at the sum and difference frequencies of the original transmissions are generated?3-56G5 How can even-order harmonics be reduced or prevented in transmitter amplifier design?3-56G6 What is the modulation type that can be a frequency hopping of one carrier or multiple simultaneous carriers?3-57H1 The deviation ratio is the: